NEARSHORE FISH COMMUNITY STRUCTURE IN THE SOUTHWEST BAY

NEARSHORE FISH COMMUNITY STRUCTURE IN THE SOUTHWEST BAY
NEARSHORE FISH COMMUNITY STRUCTURE IN THE SOUTHWEST BAY
OF FUNDY AND NORTHWEST ATLANTIC: COMPARING ASSEMBLAGES
ACROSS MULTIPLE SPATIAL AND TEMPORAL SCALES
by
Collin Arens
B.Sc. (Hon), University of New Brunswick, 2003
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
Master’s of Science
In the Graduate Academic Unit of Biology
Supervisors: David Methven, Ph.D., Dept of Biology, CRI, UNB Saint John
Kelly Munkittrick, Ph.D., Dept of Biology, CRI, UNB Saint John
Examining Board: Matthew Litvak, Ph.D., Dept. of Biology, UNB Saint John
Keith Dewar, Ph.D., Faculty of Business, UNB Saint John
This thesis has been accepted by the Dean of Graduate Studies
THE UNIVERSITY OF NEW BRUNSWICK
April, 2007
© Collin Arens, 2007
ABSTRACT
The purpose of this investigation was to assess seasonal, tidal/diel and regional
variation in the nearshore fish assemblage of the southwest Bay of Fundy, as well as
identify overlying patterns in taxonomic and functional guild structure throughout
coastal shallows of the northwest Atlantic. Within the southwest Bay of Fundy species
richness and abundance varied seasonally and were correlated with water temperature
exhibiting distinct cold and warm water assemblages throughout the year. Over a 24
hour period greater species richness and abundance were observed among samples
collected at low tide, with larger fishes captured at night. Regionally, assemblage
structure was largely influenced by habitat type with geographic proximity among sites
having little direct influence on the structure observed. Throughout the northwest
Atlantic taxonomic structure reflected existing biogeographic provinces with the
Labrador, Acadian and Virginian provinces represented, while functional guild structure
exhibited latitudinal gradients with respect to ecological type and egg dispersal.
i
ACKNOWLEDGEMENTS
There are many people who helped me in many different ways throughout the
course of this project and I owe each of them a debt of gratitude. In particular I would
like to thank my mother, Kathy Read for her support and encouragement over the years.
I would like to thank my supervisors, Dr. Dave Methven and Dr. Kelly
Munkittrick for their unending patience, guidance and feedback throughout this study, as
well as my supervisory committee Dr. Simon Courtenay and Dr. Allen Curry for their
suggestions and comments.
I would also like to thank Kevin Shaughnessey, Mark Pokorski, Jason
Casselman, Frederic Vandeperre and Joesph Pratt for their assistance throughout the
field sampling; especially during the early mornings and cold winter months when I’m
sure there were other places they would have preferred to be.
Finally, thank you to my friends and fellow graduate students; Chris Blanar,
Sandy Brasfield, Jason Casselman, Karen Gormley, Lindsay Jennings, Roshini Kassie,
Mark Pokorski, Kevin Shaughnessey, and my partner Leslie Carroll, who were always
willing to lend an ear or put on a pair of waders when I was in need.
Without the assistance of all of these people this project would not have been
possible.
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TABLE OF CONTENTS
ABSTRACT ....................................................................................................................... i
ACKNOWLEDGEMENTS .............................................................................................. ii
TABLE OF CONTENTS ................................................................................................. iii
LIST OF TABLES ............................................................................................................ v
LIST OF FIGURES ....................................................................................................... viii
LIST OF SYMBOLS AND ABBREVIATIONS ............................................................ xi
CHAPTER 1: GENERAL INTRODUCTION ............................................................... 12
1.1 Introduction .................................................................................................. 13
1.2 Literature Cited ............................................................................................ 16
CHAPTER 2: SPATIAL AND TEMPORAL VARIATION IN THE NEARSHORE
FISH ASSEMBLAGE OF THE SOUTHWEST BAY OF FUNDY .............................. 19
2.1 Abstract ........................................................................................................ 20
2.2 Introduction .................................................................................................. 21
2.3 Materials and Methods ................................................................................. 24
2.3.1 Study Area .......................................................................................... 24
2.3.2 Seasonal Sampling (Study 1) .............................................................. 24
2.3.3 Additional Sampling (Studies 2 & 3) ................................................. 26
2.3.4 Data Analyses ..................................................................................... 27
2.3.5 Functional Guild Classification .......................................................... 29
2.4 Results .......................................................................................................... 37
2.4.1 Seasonal Variation .............................................................................. 37
2.4.2 Functional Guilds................................................................................ 41
2.4.3 Regional Variation .............................................................................. 42
2.4.4 Tidal and Diel Variation ..................................................................... 44
2.5 Discussion .................................................................................................... 46
2.5.1 Seasonal Variation .............................................................................. 46
2.5.2 Functional Guilds................................................................................ 49
2.5.3 Regional Variation .............................................................................. 52
2.5.4 Tidal and Diel Variation ..................................................................... 53
2.6 Conclusion.................................................................................................... 56
2.7 Acknowledgements ...................................................................................... 57
2.8 Literature Cited ............................................................................................ 85
iii
CHAPTER 3: LATITUDINAL VARIATION IN TAXANOMIC AND FUNCTIONAL
GUILD STRUCTURE OF NEARHSORE FISH ASSEMBLAGES OF THE
NORTHWEST ATLANTIC ........................................................................................... 91
3.1 Abstract ........................................................................................................ 92
3.2 Introduction .................................................................................................. 93
3.3 Materials and Methods ................................................................................. 95
3.3.1 Sources of Data ................................................................................... 95
3.3.2 Data Analyses ..................................................................................... 96
3.3.3 Functional Guild Classification .......................................................... 97
3.4 Results ........................................................................................................ 100
3.4.1 Taxonomic Analyses ........................................................................ 101
3.4.2 Functional Guild Analyses ............................................................... 101
3.5 Discussion .................................................................................................. 104
3.6 Acknowledgements .................................................................................... 110
3.7 Literature Cited .......................................................................................... 133
CHAPTER 4: GENERAL SUMMARY AND CONCLUSIONS ................................ 136
4.1 Summary .................................................................................................... 137
4.1.1 Southwest Bay of Fundy Nearshore Fish Assemblage ..................... 137
4.1.2 Northwest Atlantic ............................................................................ 139
4.2 Conclusions ................................................................................................ 140
4.2.1 Functional Guilds.............................................................................. 140
4.2.2 Implications for Management of Nearshore Areas ........................... 142
4.2.3 Future Research ................................................................................ 142
4.3 Literature Cited .......................................................................................... 144
VITA
iv
LIST OF TABLES
Table 2.1: Name, number, location and dominant substrate type at the 16 sites sampled
in this study. Study indicates sites sampled during seasonal (1), regional (2)
and tidal/diel (3) studies. See Methods for details. ..................................... 58
Table 2.2: Functional guild classification used in this study during the 13 months of
sampling at sites 1-3 and 12-14. Abbreviations as follows: Ecological Type
- Marine Migrant (MM), Marine Straggler (MS), Estuarine Resident (ER),
Estuarine Migrant (EM), Freshwater Migrant (FM), Freshwater Straggler
(FS), Diadromous (DA). Vertical Distribution – Pelagic (P), Demersal (D).
Reproductive Strategy – Viviporous (V), Ovoviviporous (W), Oviporous
(O). Egg dispersal – Pelagic (P), Demersal (D). Residency – Regular (R),
Summer Periodic (SP), Winter Periodic (WP), Ocassional (O). Maturity –
Juvenile (J), Adult (A), Juvenile and Adult (J/A). ...................................... 59
Table 2.3: Species collected during 13 months of sampling at six sites (1-3, 12-14) in the
southern Bay of Fundy, August 2003-2004. The presence of a species at a
particular site is indicated by a black dot. ................................................... 60
Table 2.4: Correlation coefficients (r) and p values for species richness (S) and
abundance (Ni) with average temperature (˚C) and salinity (‰) at the scales
of site, region (Passamaquoddy Bay (PB) sites 1-3, Saint John Harbour
(SJH) sites 12-14) and the Bay of Fundy (sites 1-3 and 12-14). For each
calculation n = 13. ....................................................................................... 61
Table 2.5: Functional guild classifications for all species collected during seasonal
sampling in the southwestern Bay of Fundy. Abbreviations as follows:
Ecological Type - Marine Migrant (MM), Marine Straggler (MS), Estuarine
Resident (ER), Estuarine Migrnat (EM), Freshwater Migrant (FM),
Freshwater Straggler (FS), Diadromous (DA). Vertical Distribution –
Pelagic (P), Demersal (D). Reproductive Strategy – Viviporous (V),
Ovoviviporous (W), Oviporous (O). Egg dispersal – Pelagic (P), Demersal
(D). Residency – Regular (R), Summer Periodic (SP), Winter Periodic
(WP), Ocassional (O). Maturity – Juvinile (J), Adult (A), Juvinile and Adult
(J/A). ............................................................................................................ 62
v
Table 2.6: Proportional composition of functional guilds based upon species richness (S)
and abundance (Ni) of fishes collected during seasonal sampling in the
southwestern Bay of Fundy. Abbreviations as follows: Ecological Type Marine Migrant (MM), Marine Straggler (MS), Estuarine Resident (ER),
Estuarine Migrnat (EM), Freshwater Migrant (FM), Freshwater Straggler
(FS), Diadromous (DA). Vertical Distribution – Pelagic (P), Demersal (D).
Reproductive Strategy – Viviporous (V), Ovoviviporous (W), Oviporous
(O). Egg dispersal – Pelagic (P), Demersal (D). Residency – Regular (R),
Summer Periodic (SP), Winter Periodic (WP), Ocassional (O). Maturity –
Juvinile (J), Adult (A), Juvinile and Adult (J/A)......................................... 63
Table 2.7: Estimated size and age of maturity for fishes collected during seasonal
sampling in the southwest Bay of Fundy. ................................................... 64
Table 2.8: Relative abundance of fishes collected by seine during the regional sampling
at 16 sites in the southern Bay of Fundy in October. .................................. 65
Table 2.9: Species collected by seine at each of the 16 sites during the regional sampling
in the southern Bay of Fundy, October 16-22, 2004. .................................. 65
Table 2.9: Species collected by seine at each of the 16 sites during the regional sampling
in the southern Bay of Fundy, October 16-22, 2004. .................................. 66
Table 2.10: Species collected by seine over two twenty four hour sampling periods at
Black Beach, New Brunswick (site 11). Ni indicates the number of
individuals collected for each species. ........................................................ 67
Table 2.11: Summary of diel catch data collected over two twenty four hour periods
(September, October) in the southwestern Bay of Fundy at Black Beach.
Total species richness (S) and abundance (Ni) are indicated. The number of
hauls made during each time period is indicated by n. Black dots indicate
species presence. ......................................................................................... 68
Table 2.12: Summary of diel catch data collected over two twenty four hour periods
(September, October) in the southwestern Bay of Fundy at Black Beach.
Variance among hauls for species richness (S) and abundance (Ni)
indicated. The number of hauls made during each time period is indicated
by n. ............................................................................................................. 69
Table 2.13: Results of three factor ANOVAs examining influence of sampling period
(September 24-25/October 1-2), time of day (TOD, day/night) and tide
(low/mid/high), with respect to species richness and abundance. Significant
p values (<0.05) are indicated in bold. ........................................................ 70
vi
Table 2.14: Results Kruskal Wallis non-parametric ANOVAs examining potential
influences of tide and time of day on individual fish lengths collected over
two twenty four hour periods. Significant p values (<0.05) are indicated in
bold. ............................................................................................................. 71
Table 3.1: Sampling locations and protocols for data used in meta-analysis. .............. 111
Table 3.2: Species encountered in each of the 15 nearshore areas examined in the
Northwest Atlantic. The presence of a species at a particular site is indicated
by a black dot. ........................................................................................... 112
Table 3.3: Functional guild classification for each species encountered in the 15
nearshore areas examined.......................................................................... 115
Table 3.3: Functional guild classification for each species encountered in the 15
nearshore areas examined.......................................................................... 116
Table 3.4: Proportional composition of functional guilds based upon species richness (S)
and total catch (Ni) for fishes examined in the NWA. See Methods for
explanation of abbreviations. .................................................................... 119
Table 3.4: Proportional composition of functional guilds based upon species richness (S)
and total catch (Ni) for fishes examined in the NWA. See Methods for
explanation of abbreviations. .................................................................... 120
Table 3.5: Statistical results of linear regressions used to examine latitudinal variation of
functional guilds with respect to contributions made by species and
individuals. n indicates the number of sites available for comparison.
Statically significant slopes (p < 0.05) indicated in bold. ......................... 121
vii
LIST OF FIGURES
Figure 2.1: Chart of the southwest Bay of Fundy indicating sample sites used during this
investigation. Specific information for each site is listed in Table 2.1. ...... 72
Figure 2.2: Average monthly temperature (n = 13, dashed line) and salinity (n = 13,
dotted line) plotted against species richness and total monthly catch (all
species) from combined seasonal collections at six sites (1-3, 12-14) in the
southwest Bay of Fundy August 2003-2004. .............................................. 73
Figure 2.3: Seasonal patterns of species richness and abundance at site, region and bay
scales in the southwest Bay of Fundy. ........................................................ 74
Figure 2.4: Dendogram of sites 1-3 and 12-14 in the southwest Bay of Fundy as
indicated by the Bray-Curtis index of similarity and subsequent break down
of group components indicating species present and mean catch per site for
each group with n indicating the number of sites within each group. ......... 75
Figure 2.5: Dendogram of sites 1-3 and 12-14 in the southwestern Bay of Fundy as
indicated by the Bray-Curtis index of similarity using a binary data set, and
subsequent break down of species composition. Occurrence among groups
indicates the percentage of groups in which a species was collected. Within
group indicates the percentage of sites within that group each species
occurred. n indicates the number of sites within each group. ..................... 76
Figure 2.6: Dendograms identifying seasonal assemblage groupings at the site, region
and bay scales in the southwest Bay of Fundy as indicated by the BrayCurtis index of similarity using binary data. Winter grouping (January to
April) is indicated by closed circles. ........................................................... 77
Figure 2.7: Dendogram of months in the southwestern Bay of Fundy as indicated by the
Bray-Curtis index of similarity using a binary data set and subsequent break
down of species composition. Occurrence among groups indicates the
percentage of groups in which a species was collected. Within group
indicates the percentage of sites within that group each species occurred. n
indicates the number of sites within each group. ........................................ 78
Figure 2.8: Standard length (SL) of individual fish in relation to month of collection.
Dotted line indicates the approximate size of first spawning...................... 79
Figure 2.9: Species richness, abundance and percent composition of M. menidia from 16
sites sampled in the southwest Bay of Fundy between October 16 and 22,
2004. ............................................................................................................ 81
viii
Figure 2.10: Dendogram of sites 1-16 in the southwest Bay of Fundy as indicated by the
Bray-Curtis index of similarity and subsequent break down of group
components indicating species present and mean abundance per site for each
group with n indicating the number of sites within each group. ................. 82
Figure 2.11: Species richness and abundance in relation to tidal amplitude from samples
taken over two twenty four hours periods on September 24-25 and October
1-2, 2004. Night hours are indicated by the thatched area. ......................... 83
Figure 2.12: Size distribution of nearshore fishes collected over two 24 hour periods
during September and October 2004 using a seine in the southwest Bay of
Fundy. Mean length +/- standard error and median indicated. ................... 84
Figure 3.1: Location of nearshore studies used in large scale comparison. Biogeographic
provinces identified by dashed lines and italics. ....................................... 122
Figure 3.2: Number of species (closed dots, solid trend line r2: 0.954) and families (open
dots, dashed trend line r2: 0.970) encountered in nearshore collections
throughout the northwest Atlantic in relation to latitude. Cape Cod also
indicated (dotted grey line). ...................................................................... 123
Figure 3.3: Percent similarity of 15 nearshore areas examined in the northwest Atlantic
based on family data as indicated by the Bray-Curtis index using a binary
matrix. Zoogeographic provinces listed (Briggs 1974). See Table 3.1 for site
details. ....................................................................................................... 124
Figure 3.4: Percent similarity of 15 nearshore areas examined in the northwest Atlantic
based on species data as indicated by the Bray-Curtis index using a binary
matrix. Zoogeographic provinces listed (Briggs 1974).See Table 3.1 for site
details. ....................................................................................................... 125
Figure 3.5: Proportion of species and individuals exhibiting specific ecological types
across latitude. See text for guild definitions. ........................................... 126
Figure 3.6: Proportion of species and individuals exhibiting pelagic (P) or demersal (D)
vertical distributions across latitude. See text for guild definitions. ......... 128
Figure 3.7: Proportion of species and individuals exhibiting viviparous (V),
ovoviviparous (W) and oviparous (O) reproductive types across latitude.
See text for guild definitions. .................................................................... 129
Figure 3.8: Proportion of species and individuals exhibiting pelagic (P) or demersal (D)
egg dispersals across latitude. See text for guild definitions..................... 130
Figure 3.9: Proportion of species and individuals exhibiting regular (R), summer
periodic (SP), winter periodic (WP) and occasional (O) residency types
across latitude. See text for guild definitions. ........................................... 131
ix
Figure 3.10: Proportion of species and individuals exhibiting juvenile (J), adult (A) and
mixed (J/A) maturity types across latitude. See text for guild definitions. 132
x
LIST OF SYMBOLS AND ABBREVIATIONS
°C
Degrees Celsius
%
Percent
ANOVA
Analysis of Variance
ß
Beta
cm
Centimetre
CRI
Canadian Rivers Institute
df
Degrees of Freedom
hrs
Hours
m
Meter
mm
Millimetre
n
Number
N
North
Ni
Number of Individuals
NEA
Northeast Atlantic
NWA
Northwest Atlantic
ppt
Parts Per Thousand
r
Correlation Coefficient
r2
Regression
S
Species Richness
SL
Standard Length
W
West
xi
12
1 CHAPTER 1: GENERAL INTRODUCTION
13
1.1
Introduction
Estuaries and associated coastal waters are recognized as regions of high
productivity that support large densities of biomass including both fish and invertebrates
(Haedrich 1983, Elliott 2002). With respect to ichthyofauna these habitats serve as
nursery grounds for juveniles, as foraging and spawning sites for adults, and as
migratory routes for anadromous and catadromous species (McHugh 1967, Beck et al.
2003). Despite wide acceptance of the significance these habitats have for fishes at
various life history stages, several gaps exist in our current understanding of how fish
communities are structured in the northwest Atlantic and the processes that influence
species composition at different spatial and temporal scales. This information is
becoming of greater importance as regulatory bodies look to protect and manage
nearshore environments (Agardy 1994, Jamieson and Levings 2001, Beck et al. 2003).
Given that habitat and resource requirements vary among fishes and change
throughout ontogeny, species are continuously migrating in and out of the nearshore area
to meet specific biological needs. This results in a dynamic community that is constantly
changing in terms of its composition and structure. Changes in assemblage structure are
accentuated by the changing physical conditions of the estuarine environment, with
variation observed in response to factors such as tidal height, photointensity, salinity and
temperature (Haedrich 1983). Nearshore fishes compensate for the dynamic nature of
estuarine and coastal waters by occupying different habitats throughout their life cycles,
maximizing their potential for growth while reducing physiological stress and the risk of
mortality (Gibson et al. 1996, Morrison et al. 2002).
14
Traditionally our understanding of nearshore fish assemblages has largely been
focused on the analysis of taxonomic divisions (i.e., the presence, abundance and/or
biomass of species). This understanding has been extended over the past decade by
analyzing the ecological structure of nearshore ecosystems through the use of functional
guilds (e.g., Elliot and DeWailly 1995, Whitfield 1999, Mathieson et al. 2000, Thiel et
al. 2003). Functional guilds summarize the ecological structure of a fish assemblage by
grouping species according to similarities in specific biological and ecological traits
(Brown 2004) allowing for the creation and testing of models concerning the ecological
structure of a ecosystem (e.g., prevailing means of egg dispersal) which may not be
possible when examining taxonomic attributes alone. The functional guild approach is
independent of taxonomic classification and hence facilitates cross-site comparison over
large geographic areas which support distinctive biota and thus could not be readily
compared based upon phylogenic relationships alone (Gitay and Noble 1997).
Research on temperate nearshore fish assemblages in the northwest Atlantic
(NWA) has typically focused on seasonal variation among individual estuaries (e.g.,
Hillman 1977, Lazzari 1999, Layman 2000, Methven et al. 2001, Wilbur et al. 2003),
with comparatively little attention given to comparisons across large geographic areas or
at small temporal scales. However, quantifying variation at these scales is essential in
coastal zone management. Without an adequate understanding of the ecological
processes operating at these scales, monitoring programs can not account for natural
variability, confounding resulting data and limiting its effective use (Elliott 2002).
Throughout temperate regions of the northeast Atlantic (NEA) changes in
assemblage structure have been examined across large geographic areas utilizing
15
taxonomic and functional traits (Elliott and DeWailly 1995, Mathieson et al. 2000,
Elliott 2002, Thiel et al. 2003). Comparable research has been lacking throughout the
NWA given that data have previously been insufficient for analysis; particularly
throughout the Canadian Atlantic. As a consequence, past research encompassing large
geographic areas in the NWA have either focused on southern latitudes (Monteiro-Neto
1990, Vieira and Musick 1994), or have been based on data sets limited in terms of their
temporal scope and the suitability of their sampling methods for comparison (Nordlie
2003). Fortunately, considerable data have been collected from nearshore communities
of the northeast United States since the late 1990’s (e.g., Lazzari 1999, Able et al. 2002,
Wilbur et al. 2003) as well as portions of the Canadian Atlantic (e.g., Methven et al.
2001, data presented herein). As a consequence it is now possible to examine variation
over large geographic areas throughout the NWA.
There were two main objectives to this investigation. The first objective was to
assess temporal and spatial variation in the nearshore fish assemblage structure of a
previously under-described portion of the Canadian Atlantic; the southwest Bay of
Fundy. This was addressed by examining; a) temporal variability at seasonal and
tidal/diel scales; b) spatial variability throughout the region and; c) identifying prevalent
ecological characteristics through the use of functional guilds. The second objective was
to then use these data in conjunction with existing nearshore records from throughout the
NWA, ranging from Newfoundland, Canada (47° N) south to Virginia, USA (36° N),
and conduct a meta-analysis in order to identify patterns in taxonomic and functional
guild structure over a large geographic scale.
16
1.2
Literature Cited
Able, K.W., M.P., Fahay, K.L., Heck, C.T. Roman, M.A. Lazzari, and S.C. Kaiser.
2002. Seasonal distribution and abundance of fishes and decapod crustaceans in a
Cape Cod estuary. Northeastern Naturalist. 9: 285-302.
Agardy, M.T. 1994. Advances in marine conservation: The role of marine protected
areas. Trends in Ecology & Evolution. 9: 267-270.
Beck, M.W., K.L. Heck, K.W. Able, D.L. Childers, D.B. Eggleston, B.M. Gillanders,
B.S. Halpern, C.G. Hays, K. Hoshino, T.J. Minello, R.J. Orth, P.F. Sheridan, and
M.P. Weinstein. 2003. The role of nearshore ecosystems as fish and shellfish
nurseries. Issues in Ecology. 11: 1-12.
Brown, C.S., 2004. Are Functional Guilds More Realistic Management Units Than
Individual Species for Restoration? Weed Technology. 18: 1566–1571.
Elliot, M., and F. DeWailly. 1995. The structure and components of European estuarine
fish assemblages. Netherlands Journal of Aquatic Ecology. 29(3-4): 397-417.
Elliott, M., and K.L. Hemingway. 2002. Fishes in Estuaries. Blackwell Science. Oxford,
UK. 636 pp.
Gibson, R.N., L. Robb, M.T. Burrows, and A.D. Ansell. 1996. Tidal, diel and longer
term changes in the distribution of fishes on a Scottish sandy beach. Marine
Ecology Progress Series. 130: 1-17.
Gitay, H., and I.R. Noble. 1997. What are functional types and how should we seek
them? In Plant Functional Types: their relevance to ecosystem properties and
global change. (Smith, T.M., H.H. Shugart and F.I. Woodward, ed.). Cambridge
University Press. New York. 369 pp.
Haedrich, R.L. 1983. Estuarine Fishes. In Estuaries and Enclosed Seas. Ecosystems of
the World 26 (Ketchum, B.H., ed.). Elsevier Scientific, New York. pp. 183-207.
Hillman, R.E., N.W. Davis, and J. Wennemer. 1977. Abundance, diversity and stability
in shore-zone fish communities in an area of Long Island Sound affected by the
thermal discharge of a nuclear power station. Estuaries and Coastal Marine
Science. 5: 355-381.
Jamieson, G.S., and C.O. Levings. 2001. Marine protected areas in Canada—
implications for both conservation and fisheries management. Canadian Journal of
Fisheries and Aquatic Science. 58: 138–156.
17
Layman, C.A. 2000. Fish assemblage structure of the shallow ocean surf-zone on the
eastern shore of Virginia barrier islands. Estuarine, Coastal and Shelf Science. 51:
201-213.
Lazzari, M.A., S. Sherman, C.S. Brown, J. King, B.J. Joule, S.B. Chenoweth, and R.W.
Langton. 1999. Seasonal and annual variations in abundance and species
composition of two nearshore fish communities in Maine. Estuaries. 22: 636-647.
Mathieson, S., A. Cattrijsse, M.J. Costa, P. Drake, M. Elliott, J. Gardner, and J.
Marchand. 2000. Fish assemblages of European tidal marshes: a comparison based
on species, families and functional guilds. Marine Ecology Progress Series. 204:
225-242.
McHugh, J.L. 1967. Estuarine nekton. In Estuaries. (Lauff, G.H. ed.). American
Association For the Advancement of Science, Washington, DC. 83: 581-620.
Methven, D.A., R.L. Haedrich, and G.A. Rose. 2001. The fish assemblage of a
Newfoundland estuary: Diel, monthly and annual variation. Estuarine, Coastal and
Shelf Sciences. 52: 669-687.
Monteiro-Neto, C. 1990. Comparative community structure of surf zone fishes in the
Chesapeake Bight and Southern Brazil. PhD Thesis, Faculty of the School of
Marine Science, The college of William and Mary, Virginia, United States.
Morrison, M.A., M.P. Francis, B.W. Hartill, and D.M. Parkinson. 2002. Diurnal and
tidal variation in the abundance of fish fauna of a temperate tidal mudflat.
Estuarine, Coastal and Shelf Sciences. 54: 793-807.
Nordlie, F.G. 2003. Fish communities of estuarine salt marshes of eastern North
America, and comparison with temperate estuaries of other continents. Reviews in
Fish Biology and Fisheries. 13: 281-325.
Thiel, B.R., H. Cabral, and M.J. Costa. 2003. Composition, temporal changes and
ecological guild classification of the ichthyofaunas of large European estuaries – a
comparison between the Tagus (Portugal) and the Elbe (Germany). Journal of
Applied Ichthyology. 19: 330-342.
Vieira, J.P., and J.A. Musick. 1994. Fish fauna in warm-temperate and tropical estuaries
of western Atlantic. Atlântica. 16: 31-53.
Whitfield, A.K. 1999. Ichthyofaunal assemblages in estuaries: A South African case
study. Reviews in Fish Biology and Fisheries. 9: 151-186.
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Wilber, D.H., D.G. Clarke, M.H. Burlas, H. Ruben, and R.J. Will. 2003. Spatial and
temporal variability in surf zone fish assemblages on the coast of northern New
Jersey. Estuarine, Coastal and Shelf Sciences. 56: 291-304.
19
2
CHAPTER 2: SPATIAL AND TEMPORAL VARIATION IN THE
NEARSHORE FISH ASSEMBLAGE OF THE SOUTHWEST BAY OF
FUNDY
20
2.1
Abstract
The purpose of this investigation was to examine how the structure of the
nearshore fish assemblage in the southwest Bay of Fundy varied across multiple spatial
and temporal scales. Fishes were collected from a depth of approximately 1 meter using
a beach seine: 1) seasonally, sampling six sites every two weeks throughout the year; 2)
regionally, sampling 16 sites throughout the southwest Bay of Fundy over one week
and; 3) tidally, sampling a single site at two hour intervals over two 24 hour periods.
Overall the nearshore fish assemblage consisted of eighteen species and exhibited a high
degree of dominance. The majority of species occurring in the assemblage were
demersal juveniles of marine origin derived from pelagic eggs occurring periodically in
the nearshore area. Species richness and abundance varied seasonally and were
correlated with water temperature. Regional variation was influenced by substrate type
with similar habitats exhibiting similar assemblages while spatial proximity among sites
had little influence on the assemblage. Over a 24 hour period considerable variation in
richness and abundance was observed in response to tide and time of day with the
greatest diversity observed at low tide while peaks in abundance occurred at twilight.
Overall the nearshore assemblage was influenced by a number of physical and biological
factors operating at multiple spatiotemporal scales.
21
2.2
Introduction
Estuaries and associated coastal waters are regions of high primary productivity
that naturally support high densities of biomass (Haedrich 1983, Elliott 2002). These
nearshore areas are of particular importance along temperate coasts where fishes and
crustaceans use them as nurseries, foraging grounds, and spawning sites, as well as
corridors between freshwater and marine ecosystems (McHugh 1967, Beck et al. 2003).
Among estuarine fishes, habitat and resource requirements vary among species and
change throughout ontogeny. As a consequence, fishes are continuously migrating in
and out of estuaries to meet specific biological needs. This results in a dynamic
community that is constantly changing in terms of its composition and structure. These
changes in assemblage structure are accentuated by the dynamic physical conditions of
nearshore environments, with considerable changes being observed in factors such as
tidal height, photointensity, salinity and temperature (Haedrich 1983). Nearshore fishes
compensate for the dynamic nature of estuarine and coastal waters by occupying
different habitats throughout their life cycles, and maximizing their potential for growth,
while reducing physiological stress and the risk of mortality (Gibson et al. 1996). These
movements are often continuous and dynamic, operating at different spatial and
temporal scales, ranging from daily habitat shifts with the rising tide, to offshore
spawning migrations (Pitman and McAlpine 2003).
Fishes do not respond to their environment at a single spatial or temporal scale
and multi-species assemblages vary in their response to the environment due to
functional differences among those species (Pittman and McAlpine 2003). Studies
22
incorporating multiple levels of spatial and temporal scale have become an important
tool in developing a comprehensive understanding of the spatiotemporal variability
within an assemblage (Schneider 1994, Pittman and McAlpine 2003). Multi-scale
studies have become more frequent over the past 15 years, with considerable research on
nearshore marine assemblages occurring in the United States (Ayvazian et al. 1992,
Lazzari et al. 1999, Piatt et al. 1999, Wilber et al. 2003, Able et al. 2002), Australia
(Jackson and Jones 1999), Europe (Gibson et al. 1993, Lobry et al. 2003) and South
Africa (Dye 1998, Whitfield 1999). As a result, a number of common features have been
identified among these environments, such as seasonal variability in assemblage
composition and an overall dominance by juvenile fishes. However, distinct differences
are also prevalent among nearshore communities, as the structure and composition of
assemblages vary among zoogeographic provinces (e.g., Ayvazian 1992), and habitat
types (Sogard and Able 1991). Distinct differences are also present in the relative
importance of these areas for the successful recruitment of commercial finfish (Able et
al. 2002). As a consequence not all patterns in community structure are universal and
localized patterns in assemblage structure have developed within regions where species
have adapted to the meet specific physical conditions. Due to this spatial variability over
the large scale it is necessary to conduct multi-scale studies within regions of interest in
order to identify localized patterns in spatiotemporal variability specific to that area.
Unfortunately this information is still largely lacking from a number of important areas
across the globe, including areas hosting some of the world’s most productive fisheries.
In addition to multi-scale studies, our understanding of estuarine communities
has also been improved recently by examining the ecological structure of these
23
environments through functional guild analyses in addition to traditional analyses of
taxonomic attributes (i.e., the presence, abundance and/or biomass of different taxa).
The use of functional guilds was first proposed for use in estuarine ecosystems by
McHugh (1967), and has been further developed by Haedrich (1983), Elliot and
DeWailly (1995), and Whitfield (1999). This approach has the advantage of identifying
ecological variation among ecosystems (e.g., identifying the dominant means of egg
dispersal) which may not be evident when examining taxonomic attributes alone.
Additionally the functional guild approach is independent of taxonomic classification
within the fish assemblage. Therefore it allows for comparisons across zoogeographic
areas which support unique biota and could not be readily compared otherwise. To date,
the functional guild concept has mainly been applied to fish in European estuaries
(Elliott and DeWailly 1995, Mathieson et al. 2000, Thiel et al. 2003), with limited use in
North America.
The objective of this study was to assess spatial and temporal variation within a
previously under-described nearshore fish assemblage of the Canadian Atlantic; the
southwest Bay of Fundy. This was addressed by examining; a) temporal variability at
seasonal (study 1) and tidal/diel scales (study 3); b) spatial variability throughout the
region (study 2) and; c) identifying prevalent ecological characteristics through the use
of functional guilds.
24
2.3
2.3.1
Materials and Methods
Study Area
The study area was located in the southwest portion of the Bay of Fundy (c. 45°
00 N, 65° 50 W, Figure 2.1). Tides form the dominant physical variable in the region
ranging in amplitude from 6-8 m in the study area to 12 m at the head of the Bay (Trites
and Garrett 1983), resulting in strong tidal currents as well as widespread mixing of the
water column (Lotze and Milewski 2002). As a consequence of its tidal amplitude the
southwest Bay of Fundy has an extensive intertidal zone comprised of 9.7% salt marshes
and mudflats, 35.2% bedrock, and 55% of coarse sedimentary shores ranging in
composition from broken rock to sand with a low coastal relief (Thomas et al. 1983).
2.3.2
Seasonal Sampling (Study 1)
Sampling was conducted at six sites in the southwest Bay of Fundy. Three sites
were located in Passamaquoddy Bay (sites 1-3) with three additional sites located in the
vicinity of Saint John Harbour (sites 12-14, Table 2.1, Figure 2.1). Sites were chosen
based on year-round accessibility, lack of ice in winter and the presence of substrates
conducive to sampling with a small seine (e.g. areas of low coastal relief free of large
rocks and debris). Seine collections described below were made at each of the six sites
twice per month for thirteen consecutive months from August 2003 to August 2004.
During each collection, two consecutive hauls were made with the seine parallel to the
shore. To maintain comparability among samples and sites, the time required during
each haul was standardized to three minutes. The mean area covered during each haul
25
was determined to be 224 +/- 4.7 m2 based upon 48 hauls measured between July and
August 2004. All sampling was performed during the day, commencing at low tide, and
was completed within three hours, to minimize the influence of tidal and diel variability
(Lasiak 1984, Gibson et al. 1996).
All collections were made using a 9 x 1.5 m beach seine (9 mm stretch mesh)
with a central collection bag which sampled the entire water column to a depth of
approximately 1 m. Additional details on the seine and its deployment are reported in
Methven and Bajdik (1994). After each site was sampled, surface water temperature and
salinity were recorded from a depth of approximately 50 cm using a handheld
thermometer and a handheld Westover RHS-10ATC temperature compensated
refractometer.
Captured fishes were transferred to a holding tank on site, identified to species,
and counted and measured (standard length SL, nearest mm), prior to live release once
sampling at each site was completed. Occasionally, specimens requiring further scrutiny
or that were collected in extremely high abundance were anesthetised using Tricaine
Methanosulfate (TMS) and fixed in 5% formalin before being transported to the
laboratory for identification. Fish identification was based on characteristics given by
Scott and Scott (1988), Able and Fahay (1998) and Colette and Klein-MacPhee (2002).
All preserved specimens were contributed to the New Brunswick Museum ichthyology
collection in Saint John.
26
2.3.3
Additional Sampling (Studies 2 & 3)
Additional sampling was also conducted to characterize small scale temporal and
spatial variation in nearshore catches of the southwest Bay of Fundy. Jenkins and
Wheatley (1998) in southern Australia and Sogard and Able (1991) in the northwest
Atlantic identified considerable variation in fish assemblage structure among different
habitat types, while Lasiak (1984) and Gibson et al. (1996) identified significant
variation in response to tide and time of day. As a consequence, two additional studies
were conducted in order to examine the influence of these small scale processes on
species richness and abundance in the southwest Bay of Fundy. The first examined
spatial variability among various habitat types (study 2), while the other examined tidal
and diel variability (study 3). Preliminary findings from the seasonal sampling (study 1)
described above indicated the optimal period to conduct the additional sampling was in
September and October, which offered high species richness and total abundance as well
as equal hours of daylight and darkness for comparison (12:12). Collections were made
using the same sampling equipment and methods described previously unless stated
otherwise.
Regional variation (study 2) of the nearshore fish assemblage in the southwest
Bay of Fundy was examined at 16 sites spanning approximately 140 km of coastline
(sites 1-16, Table 2.1, Figure 2.1). Collections were made over a six day period from
October 17-22, 2004 with three seine hauls each two minutes in duration made at each
site. All sampling was performed during the day, commencing at low tide and was
completed within three hours in order to reduce the influence of tidal and diel variability
on the collected data (Lasiak 1984, Gibson et al. 1996).
27
Tidal (c. 6 hr) and diel (12 hr) variability (Study 3) in fish catch were examined
over two twenty four hour periods (September 24-25 and October 1-2, 2004) at Black
Beach (site 11, Table 2.1, Figure 2.1). The beach is approximately 200 m long and
bordered by rocky headlands. Due to the 9 m tidal range (Thomas 1983) and low coastal
relief typical of the area, the site exhibited an extensive intertidal zone consisting of a
uniform sandy substrate persisting throughout the intertidal zone changing to soft
sediments, primarily mud, in the subtidal zone. Sampling was conducted during the
autumn when hours of daylight equalled hours of darkness (12:12), and sampling
periods were separated by one week to allow for the comparison of contrasting tidal
cycles (e.g., low tide occurred at 3:00 pm in September while high tide occurred at the
same time in October). This approach permitted the separation of tidal and diel effects
and is similar to study designs used by Lasiak (1984) in South Africa and Gibson et al.
(1996) in Scotland. Collections were made every two hours over the two 24 hour
periods. During each two hour period three hauls of the seine, each of two minutes
duration were made for a total of 78 hauls.
2.3.4
Data Analyses
Seasonal data were examined at a monthly scale combining biweekly collections
made during the same month. Since comparable sampling effort was used during each
collection, non-transformed data were additive and combined into six 18 species (the
total number of species collected) by 13 month matrices, one for each site. Although
combining the data resulted in a loss of information (i.e., 26 samples collapsed into 13
28
for each site) it was necessary to permit the data to be examined at a monthly resolution
allowing for comparison with previous studies of seasonality (e.g. Ayvazian et al. 1992,
Lazzari et al. 1999, Methven et al. 2001).
Variation in abundance and richness were examined at the scales of site, region
and bay. The site scale is defined as the data collected from each of the six sites (1-3 and
12-14) examined independently and is based on four seine hauls per month at each site.
The regional scale is defined as data collected from Passamaquoddy Bay (sites 1-3) and
vicinity of Saint John Harbour (sites 12-14, Figure 1). Data within regions were
combined to produce two 18 species by 13 month matrices based on a total of 12 seine
hauls per month at each region. The bay scale (southwest Bay of Fundy) is defined as
site data from each of the six sites combined into a single 18 species by 13 month matrix
based upon 24 seine hauls per month. Pearson correlation coefficients were determined
for species richness and abundance from average monthly temperatures and salinities at
the site, region and bay levels of scale. All means were expressed with +/- standard
error.
Similarities in species richness and abundance were examined among sites and
months using cluster analyses based upon the Bray-Curtis coefficient of similarity (Bray
and Curtis 1957). The Bray-Curtis coefficient identifies similarities among samples
based on the species richness and abundance within each sample. This information
allows samples to be clustered into groups which have similar communities, so that
samples within each group share a greater similarity to each other than with samples
from other groups. Data were square-root transformed to reduce the influence of highly
abundant species on the final result (Field et al. 1982). In addition to this, a binary data
29
set was also analyzed using the Bray-Curtis coefficient to determine similarity among
sites and months based upon the presence/absence of each species. This analysis gives
dominant and rare species equal weighting (Field et al. 1982). All cluster analyses were
conducted using the PRIMER 5 statistical package.
Twenty-four hour variability in assemblage structure was assessed using three
factor analyses of variance (ANOVAs) to identify significant differences in species
richness as well as abundance in response to sampling period (month: September,
October), time of day (day, night) and tidal height (high tide >6m, mid tide 3-5m and
low tide <3m). Post-hoc tests of tidal impacts were also conducted in order to establish
which tidal heights were significantly different from each other (low-high, low-mid,
mid-high). Species richness data were square root transformed ( X ' = ( x + 0.5) ) and
abundance data log transformed ( X ' = log( X + 1) in order to meet the assumptions of
the ANOVA that data are normally distributed and exhibit homogeneity of variance.
Pearson correlation coefficients were used to examine relationships between species
richness and abundance with respect to tidal amplitude. Variation in length was also
examined using the Kruskal-Wallis non parametric ANOVA in response to time of day
and tide. All univariate analyses were conducted using SYSTAT 11 software.
2.3.5 Functional Guild Classification
In order to examine the ecological structure of the fish assemblage, functional
guilds were developed to classify species into discrete groups (guilds) based upon shared
biological and ecological characteristics. Each species collected throughout the seasonal
30
sampling was assigned to a single guild within each of the six guild types examined
(Table 2.2). For example, in terms of vertical distribution, species were grouped into
pelagic or demersal guilds depending where they commonly occur in the water column.
The proportional contributions made by both the number of species and the number of
individuals to each guild were then calculated in order to determined the dominant
functional traits of the southwest Bay of Fundy fish assemblage.
Given that functional guilds cover a variety of biological and ecological
characteristics, the categorization of some traits differ depending upon the
spatiotemporal scale in which they are examined. This has direct implications for how
these data can be interpreted and compared (Gitay and Noble 1997). As a consequence,
the six guild types examined in this study have been divided into static or fluid
groupings depending on whether or not they are scale dependent. The four static guild
types (ecological type, vertical distribution, reproductive type and egg dispersal), assign
species to guilds based on biological and/or ecological information which is independent
of the spatiotemporal scales examined. For example, species producing pelagic eggs do
so throughout their range. As a consequence species are assumed to belong to the
assigned guild regardless of when or where it is encountered. In situations where a
species could potentially occupy multiple guilds due to changes throughout ontogeny,
only the adult characteristics are considered. For example, Urophycis tenuis is pelagic
during the larval stage; however the demersal adult stage is used in classification. Fluid
guilds however (residency, maturity), vary depending on the spatiotemporal scale
examined. For example, with respect to the residency guild, a species occurring only
during the summer months in a temperate estuary may occur year-round in a warmer
31
environment. As a consequence, species may be assigned to different guilds depending
on when and where the data was collected. Although not all of the guilds described
below occurred in the southwest Bay of Fundy, (e.g. ovoviviparous species which are
uncommon in the Northwest Atlantic, but are present in the Northeast Pacific), they
were included to facilitate comparisons with ecosystems where they do. The
classification system used in this study was developed based upon previous work with
plant and fish communities conducted by Tyler (1971), Elliott and DeWailly (1995),
Gitay and Noble (1997), Whitfield et al. (1999), Mathieson et al. (2000), Methven et al.
(2001) and Thiel et al (2003). Able and Fahay (1998), and Collette and Klein-MacPhee
(2002) describe the general biology of each species collected in this study and were the
primary sources of information used to classify species among static guilds.
Ecological Type
Ecological type places species collected in this study into one of seven guilds and
is largely based upon the classification system proposed by Whitfield (1999) for South
African fishes. Whitfield’s (1999) guilds have been modified in this study due to the
replacement of the catadromous life history strategy with diadromous in order to include
anadromous and amphidromous fishes which were not observed in South African
waters, but also utilize estuaries largely as a migration corridor.
Each of the following guilds considers two aspects of each species’ ecology: 1)
the environment in which it spawns, and 2) the extent to which it utilizes the estuarine
environment. Fishes spawn in one of three environments: marine (M), estuarine (E), or
freshwater (F) and this is indicated by the first letter in each guild. The extent to which a
32
species utilizes the estuarine environment is indicated by the second letter. Resident
species (R) reside in estuaries throughout ontogeny. Migratory species (M) are known to
regularly move in and out of estuaries, and stragglers (S) denote adventitious species
from freshwater or marine environments that are occasionally taken in estuaries. An
additional guild was also created for diadromous species (DA) which largely use the
nearshore area as a migration corridor between fresh and saltwater spawning habitats.
Overall a total of seven different life history guilds were identified with regards to
ecological type:
•
Marine Migrants (MM) spawn in the marine environment and typically make
extensive use of estuaries as a foraging ground or nursery area during the
juvenile stages before migrating offshore (e.g., Urophycis tenuis, white hake).
•
Marine Stragglers (MS) spawn and complete their entire life cycles further
offshore but occasionally appear in the estuarine environment (e.g., Limanda
ferruginea, yellowtail flounder).
•
Estuarine Residents (ER) spawn within the estuary and reside there throughout
ontogeny (e.g., Menidia menidia, Atlantic silverside).
•
Estuarine Migrants (EM) spawn in estuaries but make extensive use of marine or
freshwater habitats during their life cycles (e.g., Gasterosteus wheatlandi,
blackspotted stickleback).
•
Freshwater Migrants (FM) spawn in freshwater but frequently migrate into
estuaries when conditions are favourable (e.g., Pungitius pungitius, ninespine
stickleback).
33
•
Freshwater Stragglers (FS) spawn and complete their entire life cycle in
freshwater but occasionally appear in estuaries (e.g., Notropis heterolepis,
blacknose shiner).
•
Diadromous (DA) species which regularly migrate between freshwater and
seawater, often residing in one environment while spawning in the other. This
guild includes anadromous (e.g., Osmerus mordax, rainbow smelt), catadromous
(e.g., Anguilla rostra, American eel) and amphidromous fishes (e.g., Eleotris
acanthopoma, sleeper).
Vertical Distribution
Vertical distribution examines the partitioning of vertical space with each species
assigned to a guild based upon their degree of association with the substratum. This type
was modified from the vertical distribution category proposed by Elliot and DeWailly
(1995) by eliminating the benthic guild since it is often difficult to distinguish between
the demersal and benthic life history traits based on information available in the
scientific literature. For example, members of the Cottidae and Gadidae families are
often in direct contact with the substrate (benthic trait) but also move throughout the
water column in close association with the substrate (demersal trait, Colette and KleinMacPhee 2002). As a consequence the vertical distribution guild type in this study
contains two guilds:
•
Pelagic species (P) which occupy the upper portions of the water column with
little direct dependence upon the substrate (e.g., Clupea harengus, Atlantic
herring).
34
•
Demersal species (D) which are closely associated with the bottom (e.g., Gadus
morhua, Atlantic cod).
Reproductive Type
Reproductive type examines the method of reproduction among estuarine fishes.
This guild category was modified from Elliott and DeWailly (1995) with the removal of
the egg dispersal and parental care sub-guilds in order to simplify analysis and
interpretation of results. This guild category contains three guilds based upon the three
reproductive strategies that exist among fishes (Bond 1996):
•
Viviparous species (V) produce free-living offspring that develop and obtain
nourishment from within the female’s body (e.g., Embiotocidae, surf perches).
•
Ovoviviparous species (W) produce free-living offspring which hatch from eggs
carried within the parent’s body without obtaining nourishment from the parent
(e.g., Syngnathidae, seahorses).
•
Oviparous species (O) produce eggs which hatch outside the adult’s body and
undergo a larval stage during ontogeny (e.g., Gadidae, cods).
Egg Dispersal
Egg dispersal examines the method of egg dispersal among oviparous fishes. The
category is modified from Elliott and DeWailly (1995) who proposed this as a sub-guild
of the oviparous reproductive type. However since oviparous fishes constitute the
majority of fishes it was felt that this functional trait was important enough to warrant its
own analyses. Viviparous or ovoviviparous which do not release free floating eggs (e.g.,
35
Syngnathus fuscus, northern pipefish) were removed from analyses. The egg dispersal
guild type contains two guilds based upon the two main dispersal strategies in oviparous
fishes (Bond 1996):
•
Pelagic egg producers (P) allow currents to facilitate the dispersal of eggs;
includes semi-demersal/pelagic eggs which drift with the current above the
substrate (e.g., Urophycis tenuis, white hake or Alosa pseudoharengus, alewife).
•
Demersal egg producers (D) which deposit eggs on the substrate minimizing
dispersal (e.g., Menidia menidia, Atlantic silverside).
Residency
Residency guilds examine the seasonal occurrence of species within the fish
assemblage sampled. Residency has been assessed by a number of authors investigating
seasonal variation of fish communities in a variety of habitats (e.g. Tyler 1971, Methven
et al. 2001). The classification system developed by Tyler (1971) has been used for
nearshore species previously (Methven et al. 2001) and was adopted for this study. The
definition of ‘regular’ species used in this study differs from previous definitions of
‘resident’ species in that these species simply occur in the nearshore area throughout the
year and individuals do not necessarily reside there throughout their lives. This
distinction is important to avoid confusion in terminology identified by Able et al.
(2002). Species were assigned to each guild based on the presence and absence of
species collected throughout the seasonal sampling of this study. The residency guild
category contains four guilds based on the seasonal occurrence each species:
36
•
Regular species (R) occur in estuaries throughout the year (e.g., Menidia
menidia, Atlantic silverside).
•
Summer Periodic species (SP) frequent estuaries during the warmer months of
the year and are absent during winter (e.g., Urophycis tenuis, white hake).
•
Winter Periodic species (WP) occur nearshore during the winter (Liparis
atlanticus, Atlantic snail fish).
•
Occasional species (O) occur rarely in estuaries (i.e., less than 10 individuals
collected) and seasonal patterns of occurrence can not be confidently determined
based on low catches.
Maturity
Maturity examines the developmental structure of the fish assemblage and has
been modified from the classification used by Methven et al. (2001). Guild membership
is based on whether a species inhabits the nearshore environment as juveniles (e.g.,
nursery species), adults (e.g., foragers) or both (e.g., residents). In order to determine
appropriate membership for each species, individuals are compared to the reported size
at first spawning given in Table 2.7:
•
Juvenile (J) includes species which occupy the nearshore environment prior to
reaching sexual maturity (e.g., Urophycis tenuis, white hake).
•
Adult (A) includes species which occupy the nearshore environment after
reaching sexual maturity (e.g., Anguilla rostra, American eel).
37
•
Mixed (J/A) includes species which occupy the nearshore environment during
both juvenile and adult life history stages (e.g., Menidia menidia, Atlantic
silverside).
2.4
Results
2.4.1 Seasonal Variation (Study 1)
A total of 2669 fish representing 18 species and 11 families were collected from
six sites during 13 months of sampling in the southwest Bay of Fundy (Table 2.3). Seven
species accounted for 96.18% of the total catch. Menidia menidia was the dominant
species and represented 53.95% of the total catch. Osmerus mordax, (18.70%), Clupea
harengus, (9.25%), Pseudopleuronectes americanus, (3.86%), Microgadus tomcod,
(3.86%), Myoxocephalus scorpius, (3.30%), and Gasterosteus wheatlandi, (3.26%) were
the next most abundant species (Table 2.3). Eleven additional species accounted for the
remaining 3.82% (Table 2.3).
Temperature and salinity varied seasonally when averaged across the six sites
sampled in the southwest Bay of Fundy (Figure 2.2). Highest temperatures occurred
from June (11.5˚C) to October (11.4˚C) reaching a maximum of 16.4˚C in August. The
lowest temperatures occurred from January (0.4˚C) to March (1.9 ˚C) reaching a
minimum in January. Salinity showed a bimodal seasonal pattern with high salinities
occurring in September (30.3 ‰) and March (30.7 ‰) followed by low salinities
occurring in May (25.5 ‰) and December (24.9 ‰, Figure 2.2).
38
Species richness (S) and total catches (Ni) were highest from June to October and
lowest from January and March (Figure 2.2). This pattern was observed at each of the
six sites sampled, although there was considerable variation (Figure 2.3). For example,
species richness at McLaren Beach (site 12) ranged from three to eight from June to
October and from zero to one at Brandy Cove (site 2) during the same period. Species
richness at all sites from January to April was consistently less than three (Figure 2.3).
Correlations between species richness and temperature throughout the 13 months of
sampling were all positive but varied among sites in terms of their significance with the
strongest correlation observed at Holts Point (site 3: r = 0.95, n = 13, p = <0.001) and the
weakest occurring at Bar Road; a neighbouring site (site 2: r = 0.23, n = 13, p = 0.460,
Table 2.4, Figure 2.1). Correlations between abundance and temperature were strongest
at the Digby Ferry Terminal (site 14: r = 0.63, n = 13, p = 0.021) and weakest at Bar
Road (site 2: r = 0.02, n = 13, p = 0.961). Strong correlations were not observed with
salinity and species richness or abundance at any of the sites. Results were highly
variable with a mixture of both positive and negative correlations at the scales of site and
region (Table 2.4). Saint John Harbour exhibited a higher mean richness (S = 5.5 +/0.8) and abundance (Ni = 147.3 +/- 33.5) throughout the year compared to
Passamaquoddy Bay (S = 3.7 +/- 0.9, Ni = 58.0 +/- 26.2). Correlations between
temperature and species richness were significant in each region (Passamaquoddy Bay: r
= 0.90, n=13, p = <0.001; Saint John Harbour r = 0.62, n = 13, p = 0.024) as well as
correlations between temperature and abundance in Saint John Harbour (r = 0.81, n =
13, p = 0.001), but not Passamaquoddy Bay (r = 0.43, n=13, p = 0.143). Correlations
39
with temperature and species richness (r = 0.85, n = 13, p = <0.001) and abundance (r =
0.75, n = 13, p = 0.003) were highest at the bay scale (Table 2.4).
The six sites sampled throughout the year in this study fused into two groups at
38% similarity based on Bray Curtis analysis of species composition and abundance
(Figure 2.4). Adjacent sites did not necessarily group together based on their spatial
proximity to each other (Figure 2.4). For example, species composition and abundance
at site 3 were more similar to sites 12 and 14 (56% similarity, Figure 2.4) than to sites 1
or 2 (38% similarity) even though site 3 was closer to site 1 (10 km) and 2 (8 km) than
sites 12 (70 km) or 14 (74 km, Figure 2.1). Species richness and abundance differed
between the two groups (group 1, S=18, Ni=2095; group 2, S=11, Ni=574) largely due to
nine species (M. aenaeus, C. lumpus, H. americanus, U. tenuis, P. virens, A. aestivalis,
A. rostrata, G. morhua and S. aquosus) with low catches that were limited to sites 3, 12
and 14 (Figure 2.4). Differences between groups 1 and 2 were also due to substantial
differences in mean catches of three relatively common species, M. menidia (429.7 and
50.3), O. mordax (139.3 and 27.0) and C. harengus (0.3 and 82.0, Figure 2.4). These
three highly mobile, pelagic schooling species (M. menidia, O. mordax, and C.
harengus) accounted for 81.9% of the catch and hence had a considerable influence on
the dendogram structure observed in Figure 2.4.
Similarity among sites was also examined using the Bray-Curtis index with a
binary data set. This removed the effect of highly abundant species on site similarity and
weighed all species equally based on their presence/absence. As a consequence, sites did
not group together in the same combinations reported above (Figure 2.4 and 2.5). Spatial
proximity was still relatively unimportant in grouping sites given that the highest percent
40
similarity occurred between two distant sites (2 and 13) that were 77 km apart (Figure
2.1). All sites exhibited greater than 50% similarity to each other with the highest
similarity occurring between sites 2 and 13 (80%). Sites divided into three main groups
with group 1 (site 3) diverging at 51% and groups 2 (sites 2, 12 and 13) and 3 (sites 1
and 14) diverging at 67% similarity (Figure 2.5). The absence of G. aculeatus and O.
mordax as well as the presence of three species unique to group 1 (G. morhua, H.
americanus, and S. aquosus) were largely responsible for this initial divergence. The
absence of C. harengus from group 3, a species found at every site in group 2 (Figure
2.5) was the species primarily responsible for separating groups 2 and 3.
Two seasonal groupings were evident when binary data were analyzed using the
Bray Curtis Index of similarity at scales of site, region and bay (Figure 2.6). A warm
water species assemblage (11.3 +/- 1.54˚C, March - December) and a colder water
assemblage (2.0 +/- 0.88˚C, January – April, Figure 2.7) occurred at all scales and sites
except site 13, although there was considerable variation among sites (Figure 2.6). At
the bay scale the two seasonal groupings diverged at 39% similarity (Figure 2.7). The
warm water assemblage exhibited a relatively high species richness (S = 18) while the
cold water assemblage consisted of relatively few species (S = 3). The three species
occurring in the cold water group (O. mordax, M. menidia, P. americanus) were also
present in the southwest Bay of Fundy during each of the warmer months, however the
remaining 15 species warm water species were absent from the cold water group (Figure
2.7).
Menidia menidia, O. mordax and P. americanus were the only species observed
year round during 13 months of sampling in the nearshore area (Figure 2.8). These
41
regular species (i.e., occur year round; terminology of Tyler 1971) ranked among the top
five in abundance (Table 2.3). Menidia menidia and O. mordax were also two of only
five species collected in which the juvenile and adults stages co-occurred in the
nearshore area (Figure 2.8). The summer periodic group (not present in winter) consisted
of 11 species, the majority of which were only as juveniles. Microgadus tomcod, G.
wheatlandi and G. aculeatus were the only summer periodic species taken in both
juvenile and adult stages (Figure 2.8). Alosa aestivalis, A. rostrata, G. morhua and S.
aquosus were occasional species having no obvious seasonal patterns due to their low
abundances (Table 2.3). A monthly increase in length for some species (M. menidia, P.
americanus, M. tomcod and G. aculeatus) suggests that the same individuals may reside
nearshore for several successive months (Figure 2.8).
2.4.2 Functional Guilds
The seven most abundant species collected during the seasonal sampling
consisted of three marine migrants (C. harengus, P. americanus, M. scorpius), two
anadromous species (O. mordax, M. tomcod), one estuarine resident (M. menidia) and
one estuarine migrant (G. wheatlandi, Tables 2.5, 2.6). Four of these species occupied
pelagic habitats (M. menidia, O. mordax, C. harengus, G. wheatlandi) while the
remaining three were demersal (M. tomcod, P. americanus, and M. scorpius). All seven
species exhibited an oviparous reproductive type and produced demersal eggs. The three
most abundant fishes were regular species occurring year round in the nearshore
environment (M. menidia, O. mordax, P. americanus), while the remaining four were
42
summer periodic species being collected only during the warmer months. Four of these
fishes utilized the nearshore environment as both adults and juveniles (M. menidia, O.
mordax, M. tomcod, G. wheatlandi) while the remaining three species occurred only
during the juvenile stage (C. harengus, P. americanus, M. scorpius, Table 2.5 and 2.6).
The guild composition of the seven most dominant species was similar to the
overall fish assemblage with some marked differences (Table 2.6). Overall the fish
assemblage of the southwest Bay of Fundy was dominated by juvenile (67%), demersal
(61%), marine migrant (50%) species, exhibiting an oviparous reproductive type (100%)
and demersal eggs (61%). Also, the majority of species occurred only during the warmer
months of the year (occasional 44%, summer periodic 39%).
The number of individuals within each functional guild varied considerably from
the species based patterns reported above (Table 2.6). From the perspective of the
number of individuals occurring in each guild the fish assemblage was dominated by
pelagic (87%), estuarine residents (56%), that occurred year round (regular 76%) in both
juvenile and adult stages (80%). These individuals were oviparous (100%) producing
pelagic eggs (98%).
2.4.3 Regional Variation (Study 2)
A total of 1372 individuals representing 11 species and 9 families were collected
from 48 samples taken at 16 sites (3 hauls/site) in the southern Bay of Fundy between
October 16 and 22, 2004 (Table 2.8). Species richness and abundance varied
considerably among sites with the highest species richness observed at site 6 (S = 6), the
43
highest abundance at site 5 (Ni = 448) and the lowest values for both richness and
abundance observed at site 1 (S = 1, Ni = 1, Table 2.9, Figure 2.9). A single dominant
species, M. menidia, accounted for 93.9% of the total catch (Table 2.8). Menidia
menidia also made up more than 50% of the catch at 12 of the 16 sites (sites 2-3, 5-10,
12, and 14-16, Figure 2.9).
Sites did not group together based upon their spatial proximity to each other
when examined using the Bray-Curtis coefficient. For example the highest percent
similarity was observed between sites 5 and 16 (91.6%, Figure 2.10) which are 61 km
apart (Figure 2.1). Sites were divided into three main groups (Figure 2.10) with group 1
consisting of a single site (site 1) that was 0.9% similar to all other sites due to the of
only one species (P. gunnellus, S = 1, Ni = 1). Group 2 consisted of eight sites (sites 2-3,
5-6, 8-9, 14 and 16) and group 3 of seven sites (4, 7, 10-13 and 15) which differed in
terms of their species richness and abundance (group 2: S = 11, Ni = 1297; group 3: S =
7, Ni = 74). Differences in abundance were largely driven by M. menidia which was high
among sites in group 2 (mean = 155.8) and low among sites in group 3 (mean = 6.0).
The presence of rare species unique to group 2 (G. aculeatus, P. gunnellus, P.
pseudoharengus and A. quadracus, Figure 2.10) was also largely responsible for the
division. Additionally, groups 2 and 3 were separated in terms of their habitat types with
6 of the 8 sites present in group 2 having a coarse substrate (gravel and rock) and 6 of
the 7 sites present in group 3 having a fine substrate (mud and sand, Table 2.1, Figure
2.10).
44
2.4.4 Tidal and Diel Variation (Study 3)
A total of 1684 fish representing 11 species and 8 families were collected in 78
samples taken over two twenty four hour sampling periods (September 24-25 and
October 1-2, 2004) at Black Beach (Table 2.10). Surface water temperatures for
September (12.2 +/- 0.2˚C) and October (11.3 +/- 0.1˚C) were consistent within each
sampling period, but varied significantly between weeks (paired t-test; t1, 24 = 6.231, two
tailed critical value = 2.178, p = < 0.001, mean difference 0.5 °C). The dominant species
taken were M. menidia, O. mordax and P. americanus. These accounted for 90.91% of
the catch in September and 94.86% of the catch in October (Table 2.10).
Significant differences in species richness and abundance were observed with
respect to tidal height (low/mid/high), while differences in time of day (day/night) were
limited to the second sampling period. Species richness and abundance were on average
higher at night than during the day (Table 2.11, mean difference 0.95 species, and 8.3
individuals/haul), with nine species and 938 individuals collected at night and seven
species and 746 individuals collected during the day (Table 2.11). The highest catches
occurred immediately after dawn and dusk resulting from peaks in the catch of M.
menidia during these periods (Figure 2.11). The highest variance in species richness
occurred during nocturnal collections while the highest variance in abundance occurred
during the day. These findings were variable among sampling periods with dissimilar
patterns observed between the first (September 24-25) and second (October 1-2)
sampling periods (Table 2.12). Results of three factor ANOVAs for species richness and
abundance with respect to sampling period (September 24-25, October 1-2), time of day
(day/night), and tide (low/mid/high), indicated a significant interaction between time of
45
day and sampling period (Table 2.13), with no significant difference observed in species
richness or abundance during the first sampling period (September 24-25), while
significant differences were observed during the second sampling period (October 1-2,
Table 2.11). With respect to tide, significant differences in both species richness and
abundance were observed (Table 2.13). Post-hoc tests identified low tide as having both
greater species richness and abundance than the other tidal phases (mid/high), while mid
and high tide were not significantly different from each other. Overall, 10 species and
955 individuals were collected at low tide, 6 species and 224 individuals at mid tide and
3 species and 505 individuals at high tide (Table 2.11, Figure 2.11). The lower species
richness observed at mid and high tides resulted from an absence of species moving into
the intertidal zone (Table 2.11), with only three pelagic species (M. menidia, O. mordax
and A. aestivalis) captured at high tide. A strong negative correlation was also observed
between species richness and tidal amplitude (r = -0.766, p = <0.001), however due to
peaks in abundance largely related to crepuscular interactions and not tidal height, a
significant correlation was not observed between abundance and tidal amplitude during
the two twenty four hour collections (r = -0.204, p = 0.073). The highest variance in
species richness occurred at low tide while the highest variance in abundance occurred at
high tide. However these findings were variable among twenty four hour periods with
different patterns observed in September and October (Table 2.12).
Tidal height and time of day also had a significant influence on the size structure
of the fish assemblage observed. Significantly larger fishes were collected at night as
well as during mid and high tides (Table 2.14, Figure 2.12). Differences between night
and day fish assemblages resulted from larger fishes migrating inshore at night
46
supplementing the smaller fishes already utilizing the area during the day (Figure 2.12).
Larger mean lengths observed at mid and high tides resulted from an absence of small
fishes moving into the intertidal zone (Figure 2.12).
2.5
Discussion
2.5.1 Seasonal Variation
Throughout 13 months of sampling in the southwest Bay of Fundy, a total of 18
species were collected with seven of these accounting for greater than 95 percent of the
overall abundance. This level of richness and degree of dominance was common among
collections using similar gears in the Acadian zoogeographic region (defined in Briggs
1974), with richness typically ranging from 18 – 24 species, while 5 – 8 of these
generally made up over 95 percent of the total abundance (e.g., Ayvazian et al. 1992,
Lazzari et al. 1999, Methven et al. 2001, Able et al. 2002, Wilbur 2004). A number of
species were common to the region with A. aestivalis, A. pseudoharengus, C. harengus,
C. lumpus, G. aculeatus, G. wheatlandi, M. aenaeus, M. menidia, O. mordax, and P.
americanus regularly found among nearshore habitats in the Gulf of Maine. Due to the
high degree of dominance in the assemblage, seasonal variation in abundance was
mainly the result of changing distributions and abundances of dominant species at
various scales (Gibson et al. 1996), while changes in species richness were largely
driven by the presence and absence of additional rare species.
Seasonal variation in species richness and abundance were correlated with water
temperature at the scale of months, however variation in salinity had little influence on
47
the assemblage structure observed. Increases in species richness and abundance with
increasing temperature were observed among the majority of sites examined. However
species richness, composition and abundance were variable among sites similar to other
studies incorporating multiple sites when examining seasonal variability (e.g., Able et al.
2002). Seasonal patterns were more evident as sites were combined and examined at the
region and bay scales, indicating it may be difficult to characterize an area based upon
collections at a single site. Seasonal relationships between species richness and
abundance with temperature have been reported for other nearshore habitats in northwest
Atlantic (Lazzari et al. 1999, Methven et al. 2001, Able et al. 2002), and Europe (Gibson
et al. 1993). However this pattern may not be universal among all nearshore
communities as Jackson and Jones (1999) did not detect a significant correlation
between species richness and abundance with temperature over a 10 year period in a
temperate region of southern Australia. Although temperature was an important variable
in structuring the nearshore assemblage of the southwest Bay of Fundy, variation in
species richness and abundance in response to changes in salinity were not apparent
among months or sites. Salinity has been shown in previous studies to play a significant
role in structuring estuarine communities (Haedrich 1983). The lower reaches of
estuaries typically exhibit higher salinities with less variability than the upper reaches
and consequently exhibit a higher species richness and abundance derived from fishes of
marine origin. Since sites sampled within the southwest Bay of Fundy were all from
coastal areas and included only the lower reaches of estuaries, these variations were not
observed.
48
Two distinct seasonal assemblages occurred in the southwest Bay of Fundy, a
warm water assemblage from May through December, and cold water assemblage from
January through April. The distinction between these two assemblages was an absence
of ichthyofauna during the winter months due to extensive offshore migrations by the
majority of nearshore species. Offshore winter migrations of estuarine fishes has been
widely observed throughout the northwest Atlantic (Ayvazian et al. 1992, Lazzari et al.
1999, Methven et al. 2001, Able et al. 2002) including areas south of Cape Hatteras
which experience relatively little seasonal variability in temperature (Ross et al. 1987,
Monteiro-Neto 1990). The warm water assemblage of the southwest Bay of Fundy was
represented by a relatively high species richness and abundance produced largely by
recruitment spikes of juvenile fishes, followed by a depopulated cold water assemblage
that was represented exclusively by low numbers of M. menidia, O. mordax and P.
americanus. Each species present during the winter months occurred year round in the
nearshore zone although the majority of individuals migrated to other areas during the
winter months with M. menidia and P. americanus migrating offshore while O. mordax
largely migrated into rivers to spawn (Collette and Klien-MacPhee 2002). Winter
emigration from the nearshore area appears to be largely driven by the avoidance of
decreasing temperatures, which commonly drop to fatal levels for many nearshore
species throughout the winter months (Schultz et al. 1998, Hales and Able 2001). Spring
immigration into the nearshore zone occurs when temperatures reach more favourable
levels, coinciding with increases in primary production and spawning migrations of
several marine species (Haedrich 1983, Mariani 2001). Seasonal fluctuations in richness
and abundance in relation to temperature have been shown to be relatively stable and
49
consistent over large temporal scales, although the composition and relative abundance
of specific species within the assemblage may change (Lazzari et al. 1999).
2.5.2 Functional Guilds
Contrasting patterns were often observed when examining contributions made by
the number of species versus to the number of individuals in a guild type. Whereas
species-based assessments gave dominant and rare species equal weighting, individualbased assessments incorporated the relative abundance of individuals in each guild. The
individual-based assessment gave a more comprehensive description of the assemblage,
but as a consequence were strongly influenced by the dominant members of the
community (i.e., M. menidia).
Ecological Type: approximately half of the species encountered were marine
migrants, followed by diadromous, estuarine resident and estuarine migrant species. This
pattern is reflected in the estuarine literature as marine migrant species typically
dominate nearshore areas (Haedrich 1983, Elliottt and DeWailly 1995, Thiel et al.
2003). However, the pattern shifts once the abundance of individuals are considered
with estuarine residents making up the majority of fishes, followed by diadromous,
marine migrant and estuarine migrant species. Similar patters were observed by Thiel et
al. (2003) where species of marine origin formed the majority in terms of species while
estuarine fishes dominated in terms of abundance.
Vertical Distribution: the majority of species collected were demersal (61%),
largely due to representative species from cottidae, gadidae and pleuronectidae families
50
which commonly use the nearshore area as a nursery. However the assemblage was
overwhelmingly dominated by pelagic fishes in terms of abundance (87%).
Reproductive Type: all of the fishes encountered in the southwest Bay of Fundy
were oviparous, the most common reproductive type among teleost fishes. Although
viviparous and ovoviviparous reproductive types have been observed in the Acadian
region (e.g., Lazzari et al. 1999), they are typically found in very low abundance. These
findings are consistent with those made among European estuaries and salt marshes
(Elliott and DeWailly 1995, Mathieson et al. 2000).
Egg Dispersal: the majority of fishes encountered produced demersal eggs, both
in terms of species richness (61%) and abundance (98%). This strategy may act as a
mechanism to retain eggs in the nearshore area where juveniles can quickly find food
and refuge upon hatching. This pattern was also observed among European estuaries by
Elliott and DeWailly (1995) where >60% of fishes produced demersal eggs.
Residency: the majority of species sampled in the nearshore zone were only
collected during the summer months, with most of these occurring in low abundances
and subsequently classified as occasional species (44%) while the remainder were
classified as summer periodic (39%). Regular species subsequently made up the
remainder of the community (17%) as winter periodic species were not observed in the
southwest Bay of Fundy. While occasional and summer periodic species were the most
common, the assemblage was dominated by regular species in terms of abundance
(76%). This is not surprising considering regular species are collected year round and
therefore have the greatest potential to continuously supplement catches and achieve the
highest abundances. The three most abundant species occurred throughout all four
51
seasons (M. menidia, O. mordax and P. americanus), albeit in relatively low numbers
during the winter months. Due to the fact the nearshore zone was largely unoccupied
during the winter, which is consistent with other work done by Lazzari et al. (1999) and
Ayvazian et al. (1992) in the Gulf of Maine area as well as Massachusetts where the
nearshore zone is largely not utilized during the winter months. The reduced species
richness and abundance of nearshore areas during the winter months is due largely to
offshore migrations by summer periodic species with only resident species remaining
nearshore, leaving a small winter community of low diversity, and abundance comprised
of only the most tolerant species (Ayvazian et al. 1992). This is not surprising
considering the near zero surface water temperatures common to these regions during
the winter months. However the same pattern persists in Virginia (Layman 2000) and
the Gulf of Mexico (Ross et al. 1987) where surface temperatures are considerably
higher during the same period. Conversely winter periodic species have been commonly
observed in more northerly areas such as Newfoundland where Methven et al (2001)
collected Liparis liparis predominantly during the coldest months of the year, as well as
in Scotland where Greenwood and Hill (2003), observed six winter periodic taxa which
also occurred predominantly during the winter months (Merlangius merlangu, Liparis
liparis, Liminada liminada, Agonus cataphractus, Myoxocephalus scorpius, and
Pomatoschistus spp.).
Maturity: the nearshore assemblage was largely made up species represented by
the juvenile stage (67%), a pattern widely observed among temperate nearshore areas
which are generally considered important nursery habitats (Haedrich 1983, Methven et
al. 2001, Beck et al. 2003). The remaining species were represented by both juvenile and
52
adults stages, primarily using the nearshore area as spawning habitat (G. wheatlandi, M.
menidia), or a migration corridor between marine and freshwater habitats (A. rostrata,
O. mordax, M. tomcod, G. aculeatus). In terms of abundance the assemblage was
dominated by species occurring in both the juvenile and adult stages (80%), which is not
surprising considering the two most abundant species, M. menidia and O. mordax are
collected throughout ontogeny, with M. menidia, spending its entire lifecycle in the
nearshore zone while O. mordax commonly uses it for a nursery, foraging as well as a
migration corridor to freshwaters during spawning.
2.5.3 Regional Variation
Among the 16 sites sampled throughout October 2004, substrate type had the
strongest influence on species composition and abundance, with similar habitats having
similar assemblages. This is consistent with previous findings in the Gulf of Maine
(Sogard and Able 1991, Able et al. 2002), and Australia (Jenkins and Wheatley 1998).
Geographic proximity among sites had little influence on the community structure
observed as relatively distant sites often exhibited greater similarity than neighbouring
ones. Similar patterns were also observed with the seasonal sampling described above as
Holts Point (site 3) and Bay Shore (site 13) exhibited a higher degree of similarity with
sites from other regions (Passamaquoddy Bay versus Saint John Harbour) than with their
own. Overall, more structurally complex substrates had the greatest richness and
abundance with soft sedimentary shores (mud and sand) exhibiting a relatively low
diversity and abundance compared to hard sediments (gravel and course rock). These
53
findings are consistent with those of Lazzari and Tupper (2002) who found higher
species richness and abundance among more structurally complex nearshore habitats in
the Gulf of Maine. Due to the fact substrate type has a strong influence on fish
assemblage structure; it may be difficult to gain a comprehensive understanding of
spatial variation in a region based solely upon collections at a single site. Additional
factors not measured during this study including environmental properties such as toxic
substances, oxygen content and light have also been shown to influence the value of
specific habitats to finfish and may be important to consider in future research when
examining variation in habitat preferences among fishes (Ryder and Kerr 1989, Peters
and Cross 1992).
2.5.4 Tidal and Diel Variation
Over a twenty four hour period the predominant changes observed in the
nearshore fish assemblage were in response to the tide and time of day, consistent with
previous research on small scale variation conducted in other nearshore ecosystems
around the world (e.g., Lasiak 1984; South Africa, Gibson et al. 1996; Scotland,
Morrison et al. 2002; New Zealand).
Tidal height played the largest role in structuring the assemblage with
significantly higher catches during low tide, averaging 2.2 more species and 14.3
individuals per haul. These findings were similar to previous work by Gibson et al.
(1996) and Lasiak (1984) who also found greater richness and abundance at low tide.
Gibson et al. (1996) attributed the lower diversity observed in high water catches to the
54
fact that they are limited to the pelagic fishes which migrate into the intertidal zone with
the rising tide, and therefore many of the demersal fishes which remain in the subtidal
regions are excluded from high water sampling. This assertion is supported by the
findings of this study as high tide catches consisted exclusively of three pelagic fishes
(M. menidia, O. mordax, A. aestivalis), while low tide catches included these pelagic
species, as well as seven additional demersal fishes not observed at high tide (A.
americanus, C. lumpus, M. tomcod, M. octodecemspinosus, M. scorpius, P. americanus,
and U. tenuis).
In terms of time of day, changes in species richness and abundance were
variable, with no significant differences observed between day and night during the first
sampling period while significant differences were observed during the second.
Although findings were inconsistent, the results of the second sampling period are
consistent with previous work by Lasiak (1984), Nash (1986), Sogard and Able (1994),
and Methven et al. (2001), who reported greater catches at night using similar gear in
similar habitats; however further research will be required in the Bay of Fundy. Previous
studies which have observed differences in richness and abundance between day and
night have partially attributed this to visual gear avoidance by fishes during the daytime,
thus reducing catch per unit effort (Stoner 1991, Casey and Myers 1998). However,
differences between day and night assemblages have still been observed in mudflats
where the high turbidity of the water makes visual gear avoidance unlikely (Morrison et
al. 2002). Within the southwest Bay of Fundy the nocturnal increase in richness during
the second sampling period was largely the result of demersal gadids collected at night
(M. tomcod, P. virens, U. tenuis) which were not captured during the day. This
55
behaviour appears to be characteristic among juvenile gadids and has been observed
previously by Methven and Bajdik (1994), Gibson et al. (1996) and Methven et al.
(2001).
Increases in abundance were also observed during twilight hours (two hours
immediately following sunrise and sunset). These twilight peaks in abundance were
largely attributed to an increase in the numbers of M. menidia, an important prey species
in the area. A similar finding was also made by Lasiak (1984) who recorded an increase
in the abundance of Pomadasys olivaceus, during the same period. An additional
increase in the abundance of M. menidia was also observed in October at 02:00, as a
group of large M. saxatilis were observed herding M. menidia inshore while feeding.
Changes in the size distribution of fishes within the assemblage were also
observed relative to the tide and time of day. In relation to time of day larger fish were
taken at night due to the addition of a larger size class moving inshore, supplementing
the individuals which occurred during the day. Similar changes in assemblage structure
have been reported previously by Ross et al. (1987), and Gibson et al. (1996), who also
found larger individuals moving inshore at night. The reason behind this may be related
to foraging behaviour as larger fishes take refuge in deeper water during the day while
moving inshore at night to feed on invertebrates as they leave the substrate (Hobson et
al. 1981). In relation to tide larger fishes were taken at mid and high tides while smaller
fishes were taken at low tide. This variability in length may be due to the fact that hauls
made at mid and high water collect only the larger, more mobile fishes which migrate
upshore with the tide (Gibson et al 1996), excluding smaller less mobile fishes which
remained in the subtidal zone.
56
2.6
Conclusion
Overall the nearshore fish assemblage of the southwest Bay of Fundy exhibited a
high degree of dominance. Species richness and abundance varied seasonally and were
strongly correlated with temperature, exhibiting highs in the summer months and lows
during winter. The majority of species occurring in the assemblage were demersal,
juveniles of marine origin hatching from pelagic eggs and migrating into the nearshore
zone during the summer months, although these patterns did not persist once abundance
was considered. Regional variation was influenced by substrate type with similar
habitats exhibiting similar communities while spatial proximity among sites had little
weight on the assemblage. Over a 24 hour period considerable variation in richness and
abundance were observed in response to tide and time of day with the greatest diversity
observed at low tide while peaks in abundance occurred at twilight. Based on the
findings of this study, the time and place sampling is conducted has considerable
influence on the community observed with the greatest diversity, abundance and size
classes collected at sites with a course substrate, during low tide, at night, and during the
summer months, while sampling during alternate periods may substantially
underestimate the richness and abundance of the assemblage (Stoner 1991). As a
consequence examining communities at multiple scales is a necessity in order to
adequately assess patterns and processes responsible for finfish variance.
57
2.7
Acknowledgements
I would like to acknowledge several people for their assistance during the course
of this study. I would like to thank Kevin Shaughnessey, Mark Pokorski, Jason
Casselman, Frederic Vandeperre and Joesph Pratt for their assistance in the field
throughout the course of sampling, as well as Mr. Bill Kerr for his time and use of his
vehicle. I would also like to thank my supervisors, Dave Methven and Kelly Munkittrick
for their guidance and support. Funding was provided by the University of New
Brunswick and the New Brunswick Innovation Foundation.
58
Table 2.1: Name, number, location and dominant substrate type at the 16 sites sampled
in this study. Study indicates sites sampled during seasonal (1), regional (2)
and tidal/diel (3) studies. See Methods for details.
Site No.
Site Name
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Brandy Cove
Bar Road
Holts Point
Greens Point
Beaver Harbour
Seeleys Cove
New River Beach
Maces Bay
Dipper Harbour
Chance Harbour
Black Beach
McLarens Beach
Bay Shore
Digby Ferry Terminal
McNamara Point
Cranberry Point
†
Determined visually
1
1
1
1
1
1
Study
Latitude (°N)
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
45° 05.095
45° 05.984
45° 08.834
45° 02.513
45° 04.222
45° 05.701
45° 07.936
45° 06.995
45° 05.422
45° 07.923
45° 09.280
45° 14.199
45° 14.635
45° 15.252
45° 15.550
45° 14.576
3
Longitude (°W)
67° 04.914
67° 03.247
66° 59.005
66° 53.289
66° 44.527
66° 38.130
66° 31.606
66° 28.720
66° 25.067
66° 20.917
66° 13.737
66° 06.074
66° 04.600
66° 03.758
66° 01.900
66° 00.340
Dominant
Substrate†
Mud
Sand
Sand
Rock
Gravel
Gravel
Sand
Gravel
Gravel
Sand
Sand
Mud
Sand
Rock
Sand
Gravel
59
Table 2.2: Functional guild classification used in this study during the 13 months of
sampling at sites 1-3 and 12-14. Abbreviations as follows: Ecological Type Marine Migrant (MM), Marine Straggler (MS), Estuarine Resident (ER),
Estuarine Migrant (EM), Freshwater Migrant (FM), Freshwater Straggler
(FS), Diadromous (DA). Vertical Distribution – Pelagic (P), Demersal (D).
Reproductive Strategy – Viviporous (V), Ovoviviporous (W), Oviporous (O).
Egg dispersal – Pelagic (P), Demersal (D). Residency – Regular (R), Summer
Periodic (SP), Winter Periodic (WP), Ocassional (O). Maturity – Juvenile (J),
Adult (A), Juvenile and Adult (J/A).
60
Table 2.3: Species collected during 13 months of sampling at six sites (1-3, 12-14) in the southern Bay of Fundy, August 2003-2004.
The presence of a species at a particular site is indicated by a black dot.
Scientific Name
Menidia menidia
Osmerus mordax
Clupea harengus
Microgadus tomcod
Pseudopleuronectes americanus
Myoxocephalus scorpius
Gasterosteus wheatlandi
Gasterosteus aculeatus
Alosa pseudoharengus
Myoxocephalus aenaeus
Pollachius virens
Cyclopterus lumpus
Hemitripterus americanus
Urophycis tenuis
Alosa aestivalis
Anguilla rostrata
Gadus morhua
Scophthalmus aquosus
Totals
Common Name
Atlantic silverside
rainbow smelt
Atlantic herring
Atlantic tomcod
winter flounder
shorthorn sculpin
blackpotted stickleback
threespine stickleback
alewife
grubby
pollock
lumpfish
sea raven
white hake
blueback herring
American eel
Atlantic cod
windowpane
Rank
1
2
3
4
4
6
7
8
9
10
11
12
13
13
15
16
16
16
Ni
1440
499
247
103
103
88
87
36
23
10
9
7
6
6
2
1
1
1
2669
%
53.95
18.70
9.25
3.86
3.86
3.30
3.26
1.35
0.86
0.37
0.34
0.26
0.22
0.22
0.07
0.04
0.04
0.04
100.00
Cumulative
%
1
2
8
6
Site Number
3 12 13
14
53.95
72.65
81.90
85.76
89.62
92.92
96.18
97.53
98.39
98.76
99.10
99.36
99.59
99.81
99.89
99.93
99.96
100.00
12
11
9
11
60
61
Table 2.4: Correlation coefficients (r) and p values for species richness (S) and
abundance (Ni) with average temperature (˚C) and salinity (‰) at the scales of
site, region (Passamaquoddy Bay (PB) sites 1-3, Saint John Harbour (SJH)
sites 12-14) and the Bay of Fundy (sites 1-3 and 12-14). For each calculation
n = 13.
Scale
S * ˚C
r
P
Ni * ˚C
r
P
Ni * ‰
r
P
0.001
0.460
<0.001
0.003
0.251
0.016
-0.10
0.20
0.07
-0.49
-0.03
0.06
-0.05
0.749
0.522
0.824
0.089
0.932
0.834
0.43
0.02
0.39
0.52
0.43
0.63
0.40
0.147
0.961
0.182
0.070
0.146
0.021
-0.04
0.16
0.05
-0.64
-0.06
0.02
-0.09
0.899
0.602
0.876
0.017
0.840
0.956
0.90
0.62
0.76
<0.001
0.024
0.06
-0.03
0.02
0.838
0.925
0.43
0.81
0.62
0.143
0.001
0.03
-0.33
-0.15
0.928
0.269
0.85
<0.001
-0.38
0.195
0.75
0.003
-0.23
0.441
Site
1
2
3
12
13
14
mean
0.79
0.23
0.95
0.76
0.34
0.65
0.62
Region
PB
SJH
mean
Bay
S*‰
r
P
62
Table 2.5: Functional guild classifications for all species collected during seasonal sampling in the southwestern Bay of Fundy.
Abbreviations as follows: Ecological Type - Marine Migrant (MM), Marine Straggler (MS), Estuarine Resident (ER),
Estuarine Migrnat (EM), Freshwater Migrant (FM), Freshwater Straggler (FS), Diadromous (DA). Vertical Distribution –
Pelagic (P), Demersal (D). Reproductive Strategy – Viviporous (V), Ovoviviporous (W), Oviporous (O). Egg dispersal –
Pelagic (P), Demersal (D). Residency – Regular (R), Summer Periodic (SP), Winter Periodic (WP), Ocassional (O).
Maturity – Juvinile (J), Adult (A), Juvinile and Adult (J/A).
Scientific Name
Anguilla rostrata
Alosa aestivalis
Alosa pseudoharengus
Clupea harengus
Osmerus mordax
Gadus morhua
Microgadus tomcod
Pollachius virens
Urophycis tenuis
Menidia menidia
Gasterosteus aculeatus
Gasterosteus wheatlandi
Myoxocephalus aenaeus
Myoxocephalus scorpius
Hemitripterus americanus
Cyclopterus lumpus
Scophthalmus aquosus
Pseudopleuronectes americanus
Ecological
Type
Vertical
Distribution
DA
DA
DA
MM
DA
MM
DA
MM
MM
ER
DA
EM
ER
MM
MM
MM
MM
MM
D
P
P
P
P
D
D
D
D
P
P
P
D
D
D
D
D
D
Functional Guild Category
Reproductive
Egg
Residency
Type
Dispersal
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
P
P
P
D
D
P
D
P
P
D
D
D
D
D
D
D
P
D
O
O
SP
SP
R
O
SP
O
O
R
SP
SP
SP
SP
O
O
O
R
Maturity
A
J
J
J
J/A
J
J/A
J
J
J/A
J/A
J/A
J
J
J
J
J
J
62
63
Table 2.6: Proportional composition of functional guilds based upon species richness (S) and abundance (Ni) of fishes collected during
seasonal sampling in the southwestern Bay of Fundy. Abbreviations as follows: Ecological Type - Marine Migrant (MM),
Marine Straggler (MS), Estuarine Resident (ER), Estuarine Migrnat (EM), Freshwater Migrant (FM), Freshwater Straggler
(FS), Diadromous (DA). Vertical Distribution – Pelagic (P), Demersal (D). Reproductive Strategy – Viviporous (V),
Ovoviviporous (W), Oviporous (O). Egg dispersal – Pelagic (P), Demersal (D). Residency – Regular (R), Summer Periodic
(SP), Winter Periodic (WP), Ocassional (O). Maturity – Juvinile (J), Adult (A), Juvinile and Adult (J/A).
Ecological
Type
MM:
MS:
ER:
EM:
FM:
FS:
DA:
Totals
S
0.50
0.00
0.11
0.06
0.00
0.00
0.33
1.00
Vertical
Distribution
Ni
0.19
0.00
0.56
0.03
0.00
0.00
0.22
1.00
D:
P:
S
0.61
0.39
Ni
0.13
0.87
1.00
1.00
Functional Guild Types
Reproductive
Egg
Type
Dispersal
V:
W:
O:
S
0.00
0.00
1.00
Ni
0.00
0.00
1.00
1.00
1.00
D:
P:
S
0.61
0.39
Ni
0.98
0.02
1.00
1.00
Residency
R:
SP:
WP:
O:
S
0.17
0.39
0.00
0.44
Ni
0.76
0.23
0.00
0.01
1.00
1.00
Maturity
J:
A:
J/A:
S
0.67
0.06
0.28
Ni
0.20
0.00
0.80
1.00
1.00
63
64
Table 2.7: Estimated size and age of maturity for fishes collected during seasonal
sampling in the southwest Bay of Fundy.
Species
Anguilla rostrata
Size at Maturity
280 – 450 mm
% Mature
100.0
Menidia menidia
Clupea harengus
50 – 80 mm
250 – 280 mm TL
44.2
0.0
Alosa aestivalis
3 to 6 years
*0.0
Alosa pseudoharengus
250 – 310 mm
Myoxocephalus aenaeus
Myoxocephalus scorpius
Cyclopterus lumpus
< 73 mm TL †
2 – 8 years
5 years, 127 mm
Gadus morhua
Microgadus tomcod
Pollachius virens
320 – 360 mm
170 mm
460 – 600 mm
0.0
4.9
0.0
Urophycis tenuis
330 – 470 mm
0.0
Gasterosteus aculeatus
40 mm
8.3
Gasterosteus wheatlandi
Hemitripterus americanus
Osmerus mordax
Pseudopleuronectes
americanus
Scophthalmus aquosus
33 – 37 mm
28 – 36 mm
120 mm
200 – 250 mm
55.2
0.0
4.0
0.0
210 – 225 mm
0.0
*Captured young of the year assumed to be immature.
†
Smallest mature specimen on record
0.0
0.0
*0.0
0.0
Source
Colette and Klein-MacPhee
(2002)
Able and Fahay (1998)
O'Brien et al. (1993),
Boyar (1968)
Colette and Klein-MacPhee
(2002)
Jessop et al. (1983), Scott and
Scott (1988)
Ennis (1969)
Ennis (1970)
Cox (1920), Davenport and
Thorsteinsson (1989)
O’Brien et al. (1993)
Schaner and Sherman (1960)
Beacham (1982), Beacham
(1983), Mayo et al. (1989)
Beacham (1983),O’Brien et al.
(1993)
Colette and Klein-MacPhee
(2002)
Rowland (1983)
Beacham (1982)
Scott and Crossman (1973)
Scott and Scott (1988)
O'Brien et al. (1993)
65
Table 2.8: Relative abundance of fishes collected by seine during the regional sampling at 16 sites in the southern Bay of Fundy in
October.
Scientific Name
Common Name
Menidia menidia
Pseudopleuronectes americanus
Cyclopterus lumpus
Gasterosteus wheatlandi
Myoxocephalus scorpius
Osmerus mordax
Ammodytes americanus
Pholis gunnellus
Gasterosteus aculeatus
Apeltes quadracus
Alosa pseudoharengus
Totals
Atlantic silverside
winter flounder
lumpfish
blackspotted stickleback
shorthorn sculpin
rainbow smelt
inshore sandlance
rock gunnel
threespine stickleback
fourspine stickleback
alewife
Ni
1288
27
19
16
7
5
3
3
2
1
1
1372
Rank
1
2
3
4
5
6
7
7
9
10
10
%
Cumulative %
93.88
1.97
1.38
1.17
0.51
0.36
0.22
0.22
0.15
0.07
0.07
100.00
93.88
95.85
97.23
98.40
98.91
99.27
99.49
99.71
99.85
99.93
100.00
65
66
Table 2.9: Species collected by seine at each of the 16 sites during the regional sampling in the southern Bay of Fundy,
October 16-22, 2004.
Scientific Name
Menidia menidia
Pseudopleuronectes americanus
Cyclopterus lumpus
Gasterosteus wheatlandi
Myoxocephalus scorpius
Osmerus mordax
Ammodytes americanus
Pholis gunnellus
Gasterosteus aculeatus
Apeltes quadracus
Alosa pseudoharengus
Totals
Site Number
Common Name
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
5
6
3
3
4
2
1
1
2
3
2
3
2
2
4
Atlantic silverside
winter flounder
lumpfish
blackspotted stickleback
shorthorn sculpin
rainbow smelt
inshore sandlance
rock gunnel
threespine stickleback
fourspine stickleback
alewife
66
67
Table 2.10: Species collected by seine over two twenty four hour sampling periods at
Black Beach, New Brunswick (site 11). Ni indicates the number of individuals
collected for each species.
Scientific Name
September 24-25, 2004
Common Name
Ni
Cyclopterus lumpus
Pollachius virens
Atlantic silverside
rainbow smelt
winter flounder
blueback herring
shorthorn sculpin
white hake
Atlantic tomcod
lumpfish
pollock
491
125
84
44
15
6
3
1
1
Scientific Name
October 1-2, 2004
Common Name
Ni
Atlantic silverside
rainbow smelt
winter flounder
shorthorn sculpin
blueback herring
longhorn sculpin
inshore sandlance
625
143
99
21
18
6
2
Menidia menidia
Osmerus mordax
Pseudopleuronectes americanus
Alosa aestivalis
Myoxocephalus scorpius
Urophycis tenuis
Microgadus tomcod
Menidia menidia
Osmerus mordax
Pseudopleuronectes americanus
Myoxocephalus scorpius
Alosa aestivalis
Myoxocephalus octodecemspinosus
Ammodytes americanus
Rank
1
2
3
4
5
6
7
8
8
Rank
1
2
3
4
5
6
7
%
63.77
16.23
10.91
5.71
1.95
0.78
0.39
0.13
0.13
%
68.38
15.65
10.83
2.30
1.97
0.66
0.22
Cumulative
63.77
80.00
90.91
96.62
98.57
99.35
99.74
99.87
100.00
Cumulative
68.38
84.03
94.86
97.16
99.12
99.78
100.00
68
Ni
n
S
Ni
Time
of Day
Day
Night
Total
21
18
39
5
9
9
469
301
770
21
18
39
7
5
7
277
637
914
42
36
78
7
9
11
746
938
1684
●
●
Tidal
Height
High
Mid
Low
Total
12
12
15
39
3
5
8
9
372
45
353
770
12
15
12
39
3
4
7
7
133
179
602
914
24
27
27
78
3
6
10
11
505
224
955
1684
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
U. tenuis
S
P. americanus
n
P. virens
Ni
O. mordax
S
M. scorpius
n
M. octodecemspinosus
Overall
M. tomcod
October
M. menidia
September
C. lumpus
Variables
A. americanus
Effect
A. aestivalis
Table 2.11: Summary of diel catch data collected over two twenty four hour periods (September, October) in the southwestern Bay of
Fundy at Black Beach. Total species richness (S) and abundance (Ni) are indicated. The number of hauls made during each
time period is indicated by n. Black dots indicate species presence.
●
●
●
●
●
●
●
●
68
69
Table 2.12: Summary of diel catch data collected over two twenty four hour periods (September, October) in the southwestern Bay of
Fundy at Black Beach. Variance among hauls for species richness (S) and abundance (Ni) indicated. The number of hauls
made during each time period is indicated by n.
Effect
Variables
September
October
Overall
n
S
Ni
n
S
Ni
n
S
Ni
Time
of Day
Day
Night
21
18
1.329
3.310
3666.933
437.859
21
18
2.062
1.320
1111.162
1419.781
42
36
1.768
2.256
2352.186
991.883
Tidal
Height
High
Mid
Low
12
12
15
0.333
2.114
0.992
6402.364
8.205
411.838
12
15
12
0.992
1.238
1.970
338.083
270.638
2839.788
24
27
27
0.636
1.088
1.986
3327.172
166.370
1605.088
69
70
Table 2.13: Results of three factor ANOVAs examining influence of sampling period
(September 24-25/October 1-2), time of day (TOD, day/night) and tide
(low/mid/high), with respect to species richness and abundance. Significant p
values (<0.05) are indicated in bold.
Source
df
MS
F-ratio
P
†
Species Richness
PERIOD
TOD
TIDE
PERIOD*TOD
PERIOD*TIDE
TOD*TIDE
PERIOD*TOD*TIDE
Error
1
1
2
1
2
2
2
66
Abundance‡
PERIOD
1
TOD
1
TIDE
2
PERIOD*TOD
1
PERIOD*TIDE
2
TOD*TIDE
2
PERIOD*TOD*TIDE
2
Error
66
†
statistics calculated using √(x+0.5)
‡
statistics calculated using log10(x+1)
0.082
2.325
3.507
0.49
0.013
0.012
0.055
0.118
0.696
19.775
29.826
4.163
0.113
0.102
0.472
0.407
<0.001
<0.001
0.045
0.894
0.903
0.626
0.041
4.02
2.962
2.516
0.27
0.109
0.507
0.243
0.169
16.56
12.2
10.364
1.114
0.449
2.088
0.682
<0.001
<0.001
0.002
0.334
0.640
0.132
71
Table 2.14: Results Kruskal Wallis non-parametric ANOVAs examining potential
influences of tide and time of day on individual fish lengths collected over
two twenty four hour periods. Significant p values (<0.05) are indicated in
bold.
Effect
Variables
n
Length (mm, SL)
mean variance
df
Kruskal-Wallis ANOVA
n
K-W
P
Time
of Day
Day
Night
746
938
59.84
65.45
127.077
721.313
1
1684
327896.5
0.027
Tidal
Height
High
Mid
Low
505
224
955
65.57
76.29
58.46
330.103
711.525
415.194
2
1684
132.1
<0.001
72
Figure 2.1: Chart of the southwest Bay of Fundy indicating sample sites used during this
investigation. Specific information for each site is listed in Table 2.1.
20
12
16
10
12
8
8
6
4
4
31
30
27
26
20
31
500
16
30
400
12
300
8
200
4
100
0
0
Temperature (°C)
600
29
28
27
26
Salinity (‰)
24
0
Abundance (Ni)
28
25
0
2
29
Salinity (‰)
14
Temperature (°C)
Species Richness (S)
73
25
24
A
S
O
N
D
J
F
M
A
M
J
J
A
Figure 2.2: Average monthly temperature (n = 13, dashed line) and salinity (n = 13,
dotted line) plotted against species richness and total monthly catch (all
species) from combined seasonal collections at six sites (1-3, 12-14) in the
southwest Bay of Fundy August 2003-2004.
74
Bay of Fundy
500
10
Abundance
8
6
4
400
300
200
100
2
0
0
A SOND J FMAMJ J A
Passamaquoddy Bay (sites 1-3)
6
4
2
Species Richness
Abundance
Species Richness
8
0
300
200
100
0
A SOND J FMAM J J A
Species Richness
Region
400
10
8
A SOND J FMAMJ J A
Saint John Harbour (sites 12-14)
10
400
8
300
Abundance
Species Richness
12
6
4
2
Site
100
0
0
A SOND J FMAMJ J A
200
A SOND J FMAMJ J A
A SOND J FMAM J J A
Site 1
Site 2
Site 3
Site 12
Site13
Site 14
A SOND J FMAM J J A
A SOND J FMAMJ J A
A SOND J FMAM J J A
A SOND J FMAMJ J A
A SOND J FMAMJ J A
A SOND J FMAM J J A
6
4
2
Abundance
0
300
200
100
0
Figure 2.3: Seasonal patterns of species richness and abundance at site, region and bay scales in the southwest Bay of Fundy.
74
75
Figure 2.4: Dendogram of sites 1-3 and 12-14 in the southwest Bay of Fundy as
indicated by the Bray-Curtis index of similarity and subsequent break down of
group components indicating species present and mean catch per site for each
group with n indicating the number of sites within each group.
76
Figure 2.5: Dendogram of sites 1-3 and 12-14 in the southwestern Bay of Fundy as
indicated by the Bray-Curtis index of similarity using a binary data set, and
subsequent break down of species composition. Occurrence among groups
indicates the percentage of groups in which a species was collected. Within
group indicates the percentage of sites within that group each species
occurred. n indicates the number of sites within each group.
77
Figure 2.6: Dendograms identifying seasonal assemblage groupings at the site, region and bay scales in the southwest Bay of Fundy as
indicated by the Bray-Curtis index of similarity using binary data. Winter grouping (January to April) is indicated by closed
circles.
77
78
Figure 2.7: Dendogram of months in the southwestern Bay of Fundy as indicated by the
Bray-Curtis index of similarity using a binary data set and subsequent break
down of species composition. Occurrence among groups indicates the
percentage of groups in which a species was collected. Within group indicates
the percentage of sites within that group each species occurred. n indicates the
number of sites within each group.
79
Summer Periodic Species
Regular Species
500
150
M. menidia
n = 1440
Abundance
400
O. mordax
n = 499
120
P. americanus
n = 103
40
90
30
150
200
60
20
100
100
30
10
50
0
0
0
0
125
200
150
75
O. mordax
C. harengus
P. americanus
100
160
120
60
75
120
90
45
50
80
60
30
25
40
30
15
0
0
A
S
O
N
D
J
F
M
A
M
J
J
0
0
A
A
S
O
N
D
J
F
M
A
M
J
J
C. harengus
n = 247
200
300
M. menidia
SL (mm)
250
50
A
A
S
O
N
D
J
F
M
A
M
J
J
A
A
S
O
N
D
J
F
M
A
M
J
J
A
Summer Periodic Species
M. scorpius
n = 88
M. tomcod
n = 103
Abundance
40
60
G. wheatlandi
n = 87
40
45
30
15
20
30
20
10
15
10
5
0
0
0
0
300
100
50
75
M. scorpius
M. tomcod
G. aculeatus
G. wheatlandi
240
80
40
60
180
60
30
45
120
40
20
30
60
20
10
15
A
S
O
N
D
J
F
M
A
M
J
J
A
0
0
0
0
A
S
O
N
D
J
F
M
A
M
J
J
A
G. aculeatus
n = 36
20
30
10
SL (mm)
25
50
75
50
A
S
O
N
D
J
F
M
A
M
J
J
A
A
S
O
N
D
J
F
M
A
M
J
J
A
Figure 2.8: Standard length (SL) of individual fish in relation to month of collection. Dotted line indicates the approximate size of first
spawning.
79
80
Summer Periodic Species
25
A. pseudoharengus
n = 23
Abundance
20
25
25
P. virens
n=9
M. aenaeus
n = 10
20
20
15
15
15
10
10
10
10
5
5
5
5
0
0
0
75
100
50
100
A. pseudoharengus
M. aenaeus
P. virens
C. lumpus
80
60
80
40
60
45
60
30
40
30
40
20
20
15
20
10
0
0
A
S
O
N
D
J
F
M
A
M
J
J
0
0
A
A
S
O
N
D
J
F
M
A
M
J
J
A
C. lumpus
n=7
20
15
0
SL (mm)
25
A
S
O
N
D
J
F
M
A
M
J
J
A
A
S
O
N
D
J
F
M
A
M
J
J
A
Summer Periodic Species
25
25
H. americanus
n=6
Abundance
20
U. tenuis
n=6
20
15
15
10
10
5
5
0
0
75
100
U. tenuis
SL (mm)
H. americanus
60
80
45
60
30
40
15
20
0
0
A
S
O
N
D
J
F
M
A
M
J
J
A
A
S
O
N
D
J
F
M
A
M
J
J
A
Figure 2.8: Continued.
80
Species Richness
81
6
4
2
0
500
Abundance
400
300
200
100
0
% Composition
M. menidia
100
80
60
40
20
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
Site
Figure 2.9: Species richness, abundance and percent composition of M. menidia from 16
sites sampled in the southwest Bay of Fundy between October 16 and 22,
2004.
82
Figure 2.10: Dendogram of sites 1-16 in the southwest Bay of Fundy as indicated by the
Bray-Curtis index of similarity and subsequent break down of group
components indicating species present and mean abundance per site for each
group with n indicating the number of sites within each group.
83
350
300
200
150
4
3
2
1
0
2
350
300
200
5
4
3
2
1
0
0
0
6
150
4
7
100
Cumulative abundance (Ni)
6
8
50
Species richness (S)
8
250
October 1-2 2004
18
22
2
6
10
14
18
Tidal amplitude (m)
0
5
100
Cumulative abundance (Ni)
2
6
50
4
7
0
Species richness (S)
6
8
250
September 24-25 2004
8
18
22
2
6
10
14
18
Time of Day (hrs)
Figure 2.11: Species richness and abundance in relation to tidal amplitude from samples
taken over two twenty four hours periods on September 24-25 and October 12, 2004. Night hours are indicated by the thatched area.
84
Diel
Night
Mean: 65.46 +/- 0.88 mm
Median: 63 mm
60
Frequency
Tidal
40
40
20
20
0
Mean: 65.56 +/- 0.81 mm
Median: 63 mm
Mid
Mean: 75.29 +/- 1.78 mm
Median: 66.5 mm
Low
Mean: 58.46 +/- 0.66 mm
Median: 60 mm
0
Day
Mean: 59.84 +/- 0.41 mm
Median: 62 mm
60
Frequency
High
60
60
40
40
20
20
0
0
50
100
150
200
250
Standrad Length (mm)
0
Frequency
60
40
20
0
0
50
100
150
200
Standrad Length (mm)
Figure 2.12: Size distribution of nearshore fishes collected over two 24 hour periods
during September and October 2004 using a seine in the southwest Bay of
Fundy. Mean length +/- standard error and median indicated.
250
85
2.8
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91
3 CHAPTER 3: LATITUDINAL VARIATION IN TAXONOMIC AND
FUNCTIONAL GUILD STRUCTURE OF NEARSHORE FISH ASSEMBLAGES
OF THE NORTHWEST ATLANTIC
92
3.1
Abstract
The purpose of this study was to examine latitudinal variation in taxonomic and
functional guild structure for nearshore fish communities of the NWA by examining 15
studies conducted between 47°N and 35°N which utilized comparable sampling
protocols. A total of 56 families and 110 species were observed among 15 nearshore
areas in the NWA. Taxa followed a unimodal pattern with respect to latitude reaching a
peak at the southern edge of Cape Cod (41.33°N) to New Jersey (39.54°N). Cluster
analyses indicated four main geographic groupings among taxa which were analogous to
those identified by Briggs (1974). There were clear distinctions made between the
Labrador, Acadian and Virginian provinces, as well as an additional grouping for the
northern portion of the Virginian province which exhibited elevated richness due to its
function as an ecotone. In terms of overall guild structure NWA nearshore fish
assemblages were dominated by marine migrant species (MM: 46.4%) followed by
estuarine residents (ER: 26.4%). The majority of these fishes were demersal (D: 63.6%)
utilizing an oviparous reproductive strategy (O: 95.5%) and produced pelagic eggs (P:
57.3%). The majority of these species occurred either infrequently or only during the
warmer months of the year (O: 47.9%, SP: 36.1%) occupying the nearshore area
exclusively during the juvenile stages (J: 54.0%). Clear latitudinal gradients were
identified for several functional guilds with significant changes in the proportions of
marine migrant, estuarine resident and diadromous fishes as well as variation in the
prevailing means of egg dispersal and proportion of periodic species.
93
3.2
Introduction
Nearshore coastal environments are widely recognized as regions of high
productivity which support high densities of biomass. In terms of fish habitat these areas
serve as nursery grounds for juveniles, as feeding and spawning sites for adults, as well
as migratory routes for diadromous species (McHugh 1967, Haedrich 1983, Elliott 2002,
Beck et al. 2003). The potential importance of nearshore areas to finfish recruitment
throughout the Northwest Atlantic has been highlighted by several authours (NWA, e.g.,
Haedrich 1983, Hoss and Thayer 1993, Beck et al. 2003), and as a consequence a
number of studies have been conducted to quantify the composition and spatiotemporal
variability of many of these communities (e.g., Ayvazian et al. 1992, Lazzari et al. 1999,
Layman 2000, Methven et al. 2001). These investigations have identified a number of
characteristic features regarding the composition and structure of nearshore communities
in the NWA, such as seasonal variability with respect to temperature, as well as an
overall dominance of juveniles. However, until recently it was difficult to make
observations and characterize structure over large spatial scales. Using the body of
information now available it is possible to conduct meta-analyses in order to examine
large scale spatial processes and establish how nearshore communities are structured
throughout the NWA.
Traditionally our understanding of nearshore fish communities has largely been
focused on the analysis of taxonomic divisions (i.e., the presence, abundance and/or
biomass of species). This understanding has been extended over the past decade by
analyzing the ecological structure of nearshore systems through the use of functional
guilds (e.g., Elliot and DeWailly 1995, Whitfield 1999, Mathieson et al. 2000, Thiel et
94
al. 2003). In essence, functional guilds are used to summarize the ecological structure of
a community by grouping species according to similarities in specific biological and
ecological traits deemed important by the investigator (Brown 2004). This approach
allows for the creation and testing of models concerning the ecological structure of a
system which may not be possible when examining taxonomic attributes alone. In
addition to this, since the functional guild approach is independent of the taxonomic
classification it facilitates cross-site comparison between communities which may
support unique biota and thus could not be readily compared based upon phylogenic
relationships (Gitay and Noble 1997).
Functional guilds have been used extensively in avian research since they were
first introduced in the late 1960’s (Root 1967, e.g., Szaro 1986, O'Connell et al. 2000,
Bishop and Myers 2005). This approach has since been adopted in several other
biological fields receiving particular attention in plant ecology (e.g., Shugart 1997,
Reich et al. 2003). With respect to estuarine ecosystems, the use of functional guilds was
first proposed by McHugh (1967), and has been further developed by several authors
including Haedrich (1983), Elliot and DeWailly (1995), Whitfield (1999) and Thiel et al.
(2003). To date, the functional guild approach has largely been applied to fish in
European estuaries (e.g., Elliott and DeWailly 1995, Mathieson et al. 2000, Thiel et al.
2003), with limited use in North America. Within the NWA, the use of functional guilds
has been rare and the information presented often incidental to the main focus of the
investigation (e.g., Tyler 1971, Able et al. 2002, Methven et al. 2001). Also due to the
differing methods used to address similar functional traits (e.g., Able 2002, Nordlie
2003), existing research lacks the consistent criterion and terminology necessary to
95
facilitate comparisons among estuaries across a large spatial scale. In order to develop a
better understanding of how different functional traits vary spatially in the NWA, a large
scale comparison using consistent criteria and terminology is required.
The purpose of this study was to examine latitudinal variation in nearshore fish
communities of the NWA. The objectives were to examine latitudinal variation in: 1)
taxonomic structure and, 2) functional guild composition.
3.3
Materials and Methods
3.3.1 Sources of Data
Community data was incorporated from 15 nearshore studies conducted
throughout the NWA ranging from Newfoundland, Canada (47° N) south to Virginia,
USA (36° N, Figure 3.1), encompassing the Labrador, Acadian, and Virginian
zoogeographic provinces; as defined in Briggs (1974).
In order to focus on large scale spatial variation throughout the NWA and avoid
confounding influences from additional spatiotemporal processes, nearshore studies
were selected for analysis primarily due to similarities in sampling protocols. Previous
research on nearshore communities have identified significant sources of spatiotemporal
variation resulting from patterns in seasonal and diel usage by finfish as well as variation
in capture efficiency of various gear types (e.g., Ayvazian et al. 1992, Lazzari et al.
1999, Methven et al. 2001). In order to compensate for these factors sampling protocols
were limited to those which: a) spanned a minimum of April to November sampling at
least every two months to increase the likelihood of capturing periodic species, b) were
96
carried out during daylight hours reducing the likelihood of enhancing richness resulting
from exclusively nocturnal species (nocturnal collections omitted from analyses for
Methven et al. 2001 and Methven unpublished), and c) utilized beach seines of various
sizes and/or shallow water trawls (<5m depth) to standardize depth and capture
efficiencies and facilitate cross-site comparisons. To maximize the quantity of studies
used in the analyses the current assessment ignores large scale temporal variability
resulting from the comparison of studies conducted over three decades, as well as
variability resulting from differences in habitats type.
3.3.2 Data Analyses
Species and abundance data were assembled for each of the 15 nearshore areas
examined in the NWA. Taxonomic similarities in community structure were analyzed at
the family and species levels of organization using the Bray-Curtis coefficient (Bray and
Curtis 1957). Data from each study were combined producing a binary matrix
(presence/absence of taxa) for family and species data, giving dominant and rare species
equal weighting (Field et al. 1982). Sites were then clustered into groups using
dendograms based upon the relative taxonomic similarity of their communities, so that
sites within each group shared a greater similarity to each other than sites from other
groups.
In order to examine changes in ecological structure with latitude, functional
guilds were developed to classify species from each site into discrete groups (guilds)
based upon shared biological and ecological characteristics. Each species examined was
97
assigned to a single guild within each of six guild types described below. The
proportional contributions made by both the number of species and the number of
individuals to each guild were calculated in order to facilitate cross-site comparison and
standardize for sampling effort. Scatter plots and subsequent regressions were then
produced for each of the 21 guilds against latitude using Systat 11 software. Regression
lines were fitted using simple linear, simple exponential or Gaussian peak curves based
on r2.
3.3.3 Functional Guild Classification
The following consists of a brief overview of guild classification, further detail
can be found in section 2.3.5.
Ecological Type
•
Marine Migrants (MM) spawn in the marine environment and typically make
extensive use of estuaries as a foraging ground or nursery area during the
juvenile stages before migrating offshore (e.g., Urophycis tenuis, white hake).
•
Marine Stragglers (MS) spawn and complete their entire life cycles further
offshore but occasionally appear in the estuarine environment (e.g., Limanda
ferruginea, yellowtail flounder).
•
Estuarine Residents (ER) spawn within the estuary and reside there throughout
ontogeny (e.g., Menidia menidia, Atlantic silverside).
98
•
Estuarine Migrants (EM) spawn in nearshore areas but make extensive use of
marine or freshwater habitats throughout their life cycles (e.g., Gasterosteus
wheatlandi, blackspotted stickleback).
•
Freshwater Migrants (FM) spawn in freshwater but frequently migrate into
coastal nearshore areas when conditions are favourable (e.g., Pungitius pungitius,
ninespine stickleback).
•
Freshwater Stragglers (FS) spawn and complete their entire life cycles in
freshwater but occasionally appear in nearshore coastal areas (e.g., Notropis
heterolepis, blacknose shiner).
•
Diadromous (DA) species which regularly migrate between fresh and salt water,
often residing in one environment while spawning in the other. This guild
includes anadromous (e.g., Osmerus mordax, rainbow smelt), catadromous (e.g.,
Anguilla rostra, American eel) and amphidromous fishes (e.g., Eleotris
acanthopoma, Sleeper).
Vertical Distribution
•
Pelagic species (P) which occupy the upper portions of the water column with
little direct dependence upon the substrate (e.g., Clupea harengus, Atlantic
herring).
•
Demersal species (D) which are closely associated with the bottom (e.g., Gadus
morhua, Atlantic cod).
Reproductive Type
99
•
Viviparous species (V) produce free-living offspring that develop and obtain
nourishment from within the female’s body (e.g., Embiotocidae).
•
Ovoviviparous species (W) produce free-living offspring which hatch from eggs
carried within the parent’s body without obtaining nourishment from the parent
(e.g., Syngnathidae).
•
Oviparous species (O) produce eggs which hatch outside the adult’s body and
undergo a larval stage during ontogeny (e.g., Gadidae).
Egg Dispersal
•
Pelagic egg producers (P) allow currents to facilitate the dispersal of eggs;
includes semi-demersal/pelagic eggs which drift with the current above the
substrate (e.g., Urophycis tenuis, white hake or Alosa pseudoharengus, alewife).
•
Demersal egg producers (D) which deposit eggs on the substrate minimizing
dispersal (e.g., Menidia menidia, Atlantic silverside).
Residency
•
Regular species (R) occur in nearshore areas throughout the year (e.g., Menidia
menidia, Atlantic silverside).
•
Summer Periodic species (SP) frequent nearshore areas during the warmer
months of the year and are absent during winter (e.g., Urophycis tenuis, white
hake).
•
Winter Periodic species (WP) frequent nearshore areas solely during the coldest
months of the year (Liparis atlanticus, Atlantic snail fish).
100
•
Occasional species (O) occur rarely in nearshore areas (i.e., less than 10
individuals sampled per site) and seasonal patterns of occurrence can not be
confidently determined based on low catches.
Maturity
•
Juvenile (J) includes species which occupy the nearshore environment prior to
reaching sexual maturity (e.g., Urophycis tenuis, white hake).
•
Adult (A) includes species which occupy the nearshore environment after
reaching sexual maturity (e.g., Anguilla rostra, American eel).
•
Mixed (J/A) includes species which occupy the nearshore environment during
both juvenile and adult life history stages (e.g., Menidia menidia, Atlantic
silverside).
3.4
Results
A total of 56 families and 110 species were observed among 15 nearshore areas
in the NWA (Table 3.2). Species richness and the number of families followed a
unimodal pattern with respect to latitude as values steadily increased until reaching a
peak spanning from the southern edge of Cape Cod (site 9, 41.33°N) to New Jersey (site
11, 39.54°N) and then decreasing toward Cape Hatteras (site 15, 35.13°N, Figure 3.2,
Table 3.2).
101
3.4.1 Taxonomic Analyses
Cluster analyses indicated four main geographic groupings among taxa. At the
family level, two groups initially diverged at 31.46% similarity (Figure 3.3). The sites
found in each of the two divisions were geographically separated from each other by the
zoogeographic boundary at Cape Cod (41.5°N); separating the northern sites (1-8,
Labrador and Acadian provinces) from the southern sites (9-15, Virginian province).
Subsequent diversions in each of these groups identified further geographic separation
with sites in the Labrador (site 1) and Acadian (sites 2-8) zoogeographic provinces
separating from each other, while in the Virginian province northern sites (9-11)
separated from southern sites (12-15, Figure 3.1). These four groups were also evident in
the species data (Figure 3.4) with the initial division at 16.79% separating southern sites
in the Virginian province (12-15), from more northerly sites (1-11). The northern group
subsequently broke down separating into the Labrador (site 1), Acadian (sites 2-8) and
northern sites from the Virginian province (sites 9-11, Figure 3.4).
3.4.2 Functional Guild Analyses
Functional guild classifications for each of the 110 species encountered
throughout the NWA are presented Table 3.3. In terms of overall guild structure based
upon species composition (Table 3.4), NWA nearshore fish assemblages were
dominated by marine migrants (MM: 46.4%) followed by estuarine residents (ER:
26.4%). The majority of these fishes were demersal (D: 63.6%) utilizing an oviparous
reproductive strategy (O: 95.5%), produced pelagic eggs (P: 57.3%) and occurred either
102
infrequently or only during the warmer months of the year (O: 47.9%, SP: 36.1%)
occupying the nearshore area exclusively during the juvenile stages (J: 54.0%). However
marked differences were observed with respect to the total catch of fishes occupying
these guilds (Table 3.4). In terms of individuals, assemblages were largely dominated by
estuarine residents (ER: 88.1%) with marine migrants of less importance (MM: 5.8%).
The majority of individuals were also pelagic (P: 77.0%) despite the prevalence of
demersal species. While the oviparous reproductive type still dominated (O: 99.8%),
these individuals largely produced demersal eggs (96.1%), and belonged to species
which occurred year round (R: 60.0%) in both juvenile and adult stages (J/A: 95.3%).
Several latitudinal gradients were also identified using regression analyses and are
examined in detail below. However, with respect to the residency and maturity guilds,
information required for classification was insufficient at some sites resulting in smaller
sample sizes and subsequent power (residency: n = 9, ß: 0.88 – 0.94, maturity: n = 7, ß:
0.93 – 0.95). As a consequence, negative results should be view critically (Table 3.5).
Ecological Type: The proportion of species exhibiting a diadromous ecological type
significantly increased with latitude (r2: 0.546, slope: 0.027, p: 0.002, Table 3.5). These
species were largely replaced by marine migrant (MM) and nearshore residents (ER) in
southern regions; however significant changes in slope for these variables were not
observed (Table 3.5). A similar pattern was also identified with respect to total catch
with diadromous individuals dominating the northern latitudes (50-44°N), while
declining in the mid and southern latitudes (r2: 0.452, slope: 0.048, p: 0.006), initially
being replaced by nearshore residents (ER) in the mid-latitudes (44-38°N) before being
103
replaced by marine migrants (r2: 0.557, slope: -0.055, p: 0.001) in the southern latitudes
(38-34°N, Figure 3.5,). The remaining ecological types occurred in low proportions
throughout the 15 nearshore areas examined in the NWA and no significant changes
were observed (Figure 3.5, Table 3.5).
Vertical Distribution: No statistically significant relationships were identified with
regards to vertical distribution and latitude (Table 3.5). The proportion of pelagic
individuals exhibited a general increase with latitude although a statistically significant
trend was not observed (r2: 0.224, slope: 0.030, p: 0.075, Figure 3.6).
Reproductive Type: No statistically significant relationships between reproductive type
and latitude were identified (Figure 3.7, Table 3.5). Nearshore finfish communities
throughout the NWA were consistently dominated by oviparous fishes (>90% of species
and individuals per site), while viviparous and ovoviviparous fishes occurred
infrequently and in low abundance.
Egg Dispersal: A significant relationship was identified between egg dispersal and
latitude (Table 3.5). The proportion species producing demersal eggs significantly
increased with latitude (Species r2: 0.881, slope: 0.044, p: <0.001, Abundance r2: 0.624,
slope 0.040, p: <0.001) while pelagic egg producers exhibited the opposite trend (Figure
3.6, Table 3.5).
104
Residency: The proportion of summer periodic species significantly decreased with
increasing latitude (r2: 0.546, slope: -0.013, p: 0.023, Table 3.5, Figure 3.9). However no
significant relationships were identified in relation to the remaining residency types.
Only a single winter periodic species was observed (Liparis liparis, site 1).
Maturity: No statistically significant patterns were observed with maturity and latitude
(Table 3.5) however the proportion of species occurring as both juveniles and adults
generally increased with latitude while juveniles generally decreased (Figure 3.10).
3.5
Discussion
Taxonomic structure of the 15 nearshore finfish assemblages examined in the
NWA reflected existing biogeographic provinces for coastal biota in the region (Briggs
1974); with detectable differences in taxa among the Labrador, Acadian and Virginian
provinces. This supports current hypotheses that Cape Cod (41.5°N) and the Avalon
Peninsula (46.6°N) act as biogeographic boundaries delineating thermal regimes and
subsequently dividing taxa based on their physiological tolerances to varying
environmental conditions (Briggs 1974, Ayvazian et al. 1992). The influence of these
biogeographic boundaries was particularly evident when taxa were examined at the
family level, however on top of these established boundaries, an additional division was
observed within the Delaware Bay region (38.8°N) of the Virginian province. This
division was also apparent when taxa were compared at the species level, with sites
south of Delaware Bay showing a low degree of similarity relative to the remaining sites
105
examined. The cause of this is divergence is mostly likely due to the role of the northern
portion of the Virginian province as a transitional zone between the Acadian and
Virginian regions. Due to the mixing of cold water from the Labrador Current and warm
water from the Gulf Stream in this region suitable conditions are produced for species
native to either province. This premise is supported by considerable overlap in species
composition observed from both Acadian and Virginian taxa in the region not observed
elsewhere.
With respect to functional guild structure NWA nearshore fish assemblages were
dominated by marine migrant species (MM: 46.4%) followed by estuarine residents
(ER: 26.4%) similar to previous findings by Ayvazian et al. (1992). The majority of
these fishes were demersal (D: 63.6%), utilizing an oviparous reproductive strategy (O:
95.5%) consistent with observations for the Northeast Atlantic (NEA) made by Elliott
and DeWailly (1995). The majority of these species produced pelagic eggs (P: 57.3%)
and occurred either infrequently or only during the warmer months of the year (O:
47.9%, SP: 36.1%) occupying the nearshore area exclusively during the juvenile stages
(J: 54.0%). However marked differences were observed with respect to the total catch of
fishes occupying these guilds similar to findings by Thiel et al. (2003) who compared
the proportion of species and the proportion of individuals contributing to various
ecological guilds. In terms of individuals, assemblages were largely dominated by
estuarine residents (ER: 88.1%) with marine migrants of less importance (MM: 5.8%).
The majority of individuals were also pelagic (P: 77.0%) despite the prevalence of
demersal species. While the oviparous reproductive type still dominated (O: 99.8%),
these individuals largely produced demersal eggs (96.1%), and belonged to species
106
which occurred year round (R: 60.0%) in both juvenile and adult stages (J/A: 95.3%).
Several relationships were identified among various species traits and latitude:
Ecological Type: The majority of species encountered in the NWA were diadromous,
estuarine residents or marine migrants; however their relative proportions changed with
latitude. Diadromous fishes dominated the northern latitudes while estuarine residents
dominated the mid latitudes and marine migrants the south. These findings were
consistent with previous work on latitudinal variation of ecological guilds by Helfman et
al. (1997) and Nordlie (2003). This trend was particularly evident when ecological
guilds were examined based on the proportion of individuals occupying these guilds.
Remaining ecological types (MS, EM, FM, and FS) remained in very low proportions
and subsequently did not constitute a major component of the nearshore fish assemblage
of the NWA.
Vertical Distribution: Significant variation in vertical distribution was not detected in
relation to latitude. Although this appears to be true with respect to the number of
species, a general decrease in the proportion of demersal individuals with decreasing
latitude was observed.
Reproductive Type: Oviparous fishes dominated the nearshore area of the NWA with
viviparous and ovoviviparous fishes occurring rarely and in low abundance. Similar
patterns were also observed by Elliott and DeWailly (1995) for European estuaries;
however it should be noted that viviparous and ovoviviparous fishes have been show to
107
constitute important portions of other nearshore communities, such as the east Pacific
(e.g., Embiotocidae).
Egg Dispersal: The proportion of species and the proportion of individuals producing
demersal eggs significantly increased with latitude which may reflect corresponding
latitudinal changes in ecological structure. Since diadromous fishes and estuarine
resident fishes dominate the northern latitudes and largely spawn within nursery areas
(whether nearshore or freshwater) they produce demersal eggs to limit dispersal, while
marine migrant species which dominated the southern latitudes typically spawn pelagic
eggs further offshore allowing ocean currents to distribute offspring throughout the
intended nursery area.
Residency: Although few significant latitudinal trends were identified with respect to
residency type, a significant increase in the proportion of summer periodic species was
observed from north to south. This observation was consistent with Tyler’s (1971)
previous predictions regarding changing residency types with latitude for coastal fishes
of the NWA, however is not consistent with respect to the underlying processes
responsible. Tyler’s (1971) hypothesis stated that more southern coastal waters have a
greater annual temperature range resulting in less thermally stable environments and
hence fewer species can occupy these areas year round. However, unlike the deeper
coastal environments Tyler (1971) based his predictions on, temperatures in shallow
nearshore areas exhibit less variability, and throughout the study area ranged by 15.0°C
at 45°N (site 3) to 16.7°C at 35°N (site 15), exhibiting minimal change with latitude. As
108
a consequence, although the pattern observed fits Tyler’s (1971) prediction, it is not
consistent with the mechanisms outlined in his hypothesis and additional factors such as
increased competition would have to be responsible for the southern increase in periodic
species observed for the nearshore area.
Maturity: Overall nearshore areas throughout the NWA were widely used as nursery
areas consistent with previous findings throughout the region (e.g., Lazzari et al. 1999,
Methven et al. 2001, Beck et al. 2003). Although no statistically significant patterns
were observed with latitude these analyses were based on a low sample size (n=7) and
should be viewed critically. In general the proportion of fishes occurring exclusively in
the juvenile stages decreased with latitude. This may indicate a greater reliance of fishes
on the nursery function of nearshore areas among southern latitudes. This observation
likely reflects the increased proportion of marine migrant fishes throughout these areas
which commonly inhabit nearshore areas solely during the juvenile stage, prior to
migrating into deeper waters during later life history stages.
The functional guild approach has been proven to be a valuable tool in describing
the ecological structure of finfish assembalges (Elliott and DeWailly 1995, Whitfield et
al. 1999, Mathieson et al. 2000, Thiel et al. 2003); however its suitability for making
large scale comparisons is currently limited by inconsistent terminology as well as
inadequate biological information. Due to the inherent flexibility of functional guilds in
describing ecological traits (Brown 2004), considerable variation in terminology exists
with investigators often using different approaches to describe similar concepts (e.g.,
ecological type: Ayvazian et al. 1992, Elliott and DeWailly 1995, Whitfield et al. 1999,
109
Nordlie 2003). Due to the fact these approaches are rarely standardized, making
comparisons between studies is often impractical without reanalyzing data. These
inconsistencies also extend to the functional guild concept itself, as multiple synonyms
are currently used throughout ecological research (e.g., ‘species traits’, functional traits’,
and ‘ecological guilds’ discussed in Wilson 1999) and as a consequence the existing
body of literature is largely unorganized impeding accurate reviews of existing
information. In order to facilitate future comparisons the adoption of a standardized
approach will be necessary for finfish communities. A second obstacle for large scale
analyses regards the quality of data currently available for accurate species
classification. As discussed by Elliott and DeWailly (1995) the functional guild
approach has a fundamental difficulty given that the biology of even common species
has not been thoroughly documented, as a consequence classifications are often based on
unconfirmed reports or characteristics of members of the same genus. As a result
reliability of species classifications are difficult to assess due to the potential for
misclassification and as a consequence designations need to be viewed critically.
Overall nearshore fish community structure of the NWA was consistent with
previous observations made for coastal fishes of the region. Biogeographic provinces
were analogous to those identified by Briggs (1974) with the exception of the northern
portion of the Virginian province which exhibited elevated richness due to its location in
a transition area for nearshore fishes. Latitudinal gradients were identified in relation to
ecological type, egg dispersal and residency indicating the presence of latitudinal
variation in functional guild structure of the NWA, however further research will be
required in order to identify the processes responsible for these patterns.
110
3.6
Acknowledgements
I would like to thank my supervisors David Methven and Kelly Munkittrick, for
their thoughts and guidance while preparing this chapter. I would also like to thank Jeff
Houlahan and members of my supervisory committee, Allen Curry and Simon
Courtenay for their feedback and additional input regarding the use of functional guilds
for marine fish assemblages.
111
Table 3.1: Sampling locations and protocols for data used in meta-analysis.
Study
No.
Authour/Location
1
Methven et al. 2001
Canada, NL, Bellevue
Methven et al. Unpublished
Canada, NB, Saint John
Chapter 2, Seasonal Data
Canada, NB, Saint John
Chapter 2, Seasonal Data
Canada, NB, Passamaquoddy Bay
Lazzari et al. 1999
USA, ME, Kennebec Point
Ayvazian et al. 1992
USA, ME, Wells Estuary
Wilbur 2004
USA, MA, Gloucester
Able et al. 2002
USA, MA, Nauset Marsh
Ayvazian et al. 1992
USA, MA, Waquoit Bay
Hillman 1977
USA, CN, Long Island Sound
Rountree and Able 1992
USA, NJ, Great Bay
Layman 2000
USA, VA, Hog Island
Schauss 1977
USA, VA, Lynnhaven Bay
Monteiro-Neto 1990
USA, VA, Cape Henry
Monteiro-Neto 1990
USA, VA, Cape Hatteras
2
3
4
5
6
7
8
9
10
11
12
13
14
15
†
Seine used in conjunction with a weir
Latitude
Longitude
# of
Sampling
Sites
Period
Gear
Sampling
Resolution
Type
Biweekly1
Seine
9m x 1.5m (9mm)
Monthly
Seine
9m x 1.5m (9mm)
Dimensions (mesh)
47° 38' N
53° 43' W
1
45° 15' N
66° 01' W
2
07/1982 - 09/1983
07/1989 - 09/1990
11/2002 - 12/2003
45° 14' N
66° 05' W
3
08/2003 - 08/2004
Biweekly
1
Seine
9m x 1.5m (9mm)
45° 06' N
67° 03' W
3
08/2003 - 08/2005
Biweekly1
Seine
9m x 1.5m (9mm)
43° 45' N
69° 45' W
2
04/1990 - 12/1994
Biweekly1
43° 19' N
70° 30' W
10
04/1988 - 12/1989
Monthly
42° 35' N
70° 40' W
4
06/1998 - 07/1999
Monthly
Seine
Fyke
Seine
Trawl
Seine
36m x 1.8m (8mm)
1.2m (7mm)
15m x 2m (4.8mm)
4.9m (4.8mm)
15m x 1.2m (4.8mm)
41° 49' N
69° 56' W
3
08/1985 - 12/1985
Bimonthly2
Seine
7.5m (6mm)
41° 33' N
70° 31' W
8
03/1988 - 12/1989
Monthly
41° 18' N
72° 10' W
6
05/1969 - 12/1972
Bimonthly2
Seine
Trawl
Seine
15m x 2m (4.8mm)
4.9m (4.8mm)
9m x 1.2m (6mm)
39° 32' N
74° 17' W
3
Biweekly1
Seine
18 x 1.2m (6.4mm)†
37° 24' N
75° 41' W
1
04/1988 - 11/1988
04/1989 - 10/1989
08/1997 - 10/1998
1
Seine
8m x 1.5m (4.8mm)
37° 54' N
76° 05' W
16
02/1973 - 01/1974
Monthly
Seine
3m x 1.2m (5mm)
36° 48' N
75° 56' W
1
07/1973 - 06/1974
Monthly
Seine
15.2 x 1.8m (6.4mm)
35° 13' N
75° 31' W
1
07/1973 - 06/1974
Monthly
Seine
15.2 x 1.8m (6.4mm)
Biweekly1: Every two weeks
Biweekly
Bimonthly2: Every two months
111
112
Table 3.2: Species encountered in each of the 15 nearshore areas examined in the Northwest Atlantic. The presence of a species at a
particular site is indicated by a black dot.
Family
Species
1
Achiridae
Ammodytidae
Anguillidae
Atherinopsidae
Batrachoididae
Belonidae
Carangidae
Chaetodontidae
Clupeidae
Congridae
Cottidae
Cyclopteridae
Cynoglossidae
Cyprinidae
2
3
4
5
6
Site Number
7 8 9 10
11
12
13
14
15
Biogeographic Province
Labrador Acadian Virginian
Trinectes maculatus
Ammodytes americanus
Anguilla rostrata
Membras martinica
Menidia beryllina
Menidia menidia
Opsanus tau
Scomberesox saurus
Strongylura marina
Tylosurus acus
Caranx crysos
Caranx hippos
Caranx latus
Selene vomer
Trachinotus carolinus
Trachinotus falcatus
Trachinotus goodei
Chaetodon ocellatus
Alosa aestivalis
Alosa mediocris
Alosa pseudoharengus
Alosa sapidissima
Brevoortia tyrannus
Clupea harengus
Sardinella aurita
Conger oceanicus
Myoxocephalus aenaeus
Myoxocephalus scorpius
Cyclopterus lumpus
Liparis atlanticus
Symphurus plagiusa
Notropis bifrenatus
112
113
Table 3.2 (cont’d): Species encountered in each of the 15 nearshore areas examined in the Northwest Atlantic. The presence of a
species at a particular site is indicated by a black dot.
Family
Species
1
Cyprinidae
Cyprinodontidae
Diodontidae
Elopidae
Engraulidae
Ephippidae
Fistulariidae
Fundulidae
Gadidae
Gasterosteidae
Gerreidae
Gobiesocidae
Gobiidae
Hemiramphidae
Hemitripteridae
Labridae
2
3
4
5
6
Site Number
7 8 9 10
11
12
13
14
15
Biogeographic Province
Labrador Acadian Virginian
Notropis heterolepis
Cyprinodon variegatus
Chilomycterus schoepfii
Elops saurus
Anchoa hepsetus
Anchoa mitchilli
Chaetodipterus faber
Fistularia tabacaria
Fundulus diaphanus
Fundulus heteroclitus
Fundulus majalis
Lucania parva
Enchelypous cimbrius
Gadus morhua
Gadus ogac
Microgadus tomcod
Pollachius virens
Urophycis chuss
Urophycis tenuis
Apeltes quadracus
Gasterosteus aculeatus
Gasterosteus wheatlandi
Pungitius pungitius
Eucinostomus argenteus
Gobiesox strumosus
Ctenogobius boleosoma
Evorthodus lyricus
Gobiosoma bosc
Hemiramphus brasiliensis
Hyporhamphus unifasciatus
Hemitripterus americanus
Tautoga onitis
113
114
Table 3.2 (cont’d): Species encountered in each of the 15 nearshore areas examined in the Northwest Atlantic. The presence of a
species at a particular site is indicated by a black dot.
Family
Species
1
Labridae
Lutjanidae
Monacanthidae
Moronidae
Mugilidae
Nomeidae
Ophidiidae
Osmeridae
Paralichthyidae
Pholidae
Pleuronectidae
Poeciliidae
Pomatomidae
Rachycentridae
Rajidae
Sciaenidae
Scophthalmidae
Serranidae
2
3
4
5
6
Site Number
7 8 9 10
11
12
13
14
15
Biogeographic Province
Labrador Acadian Virginian
Tautogolabrus adspersus
Lutjanus griseus
Aluterus schoepfii
Stephanolepis hispidus
Morone americana
Mugil cephalus
Mugil curema
Psenes sp.
Ophidion marginatum
Mallotus villosus
Osmerus mordax
Paralichthys dentatus
Paralichthys squamilentus
Pholis gunnellus
Limanda ferruginea
Pleuronectes putnami
Pseudopleuronectes
americanus
Gambusia affinis
Pomatomus saltatrix
Rachycentron canadum
Amblyraja radiata
Bairdiella chrysoura
Cynoscion nebulosus
Cynoscion regalis
Leiostomus xanthurus
Menticirrhus littoralis
Menticirrhus saxatilis
Micropogonias undulatus
Sciaenops ocellatus
Scophthalmus aquosus
Centropristis striata
114
115
Table 3.2 (cont’d): Species encountered in each of the 15 nearshore areas examined in the Northwest Atlantic. The presence of a
species at a particular site is indicated by a black dot.
Family
Species
Sparidae
Lagodon rhomboides
Stenotomus chrysops
Sphyraena borealis
Ulvaria subbifurcata
Peprilus triacanthus
Syngnathus floridae
Syngnathus fuscus
Syngnathus louisianae
Synodus foetens
Sphoeroides maculatus
Mustelus canis
Prionotus carolinus
Prionotus evolans
Prionotus tribulus
Astroscopus guttatus
Sphyraenidae
Stichaeidae
Stromateidae
Syngnathidae
Synodontidae
Tetraodontidae
Triakidae
Triglidae
Uranoscopidae
Total
56
110
1
2
3
4
5
6
Site Number
7
8
9
17
12
14
16
18
24
20
23
49
10
11
12
13
14
15
35
44
25
26
36
18
Biogeographic Province
Labrador Acadian Virginian
17
38
99
115
116
Table 3.3: Functional guild classification for each species encountered in the 15 nearshore areas examined.
Family
Achiridae
Ammodytidae
Anguillidae
Atherinopsidae
Batrachoididae
Belonidae
Carangidae
Chaetodontidae
Clupeidae
Congridae
Cottidae
Cyclopteridae
Cynoglossidae
Cyprinidae
Species
Trinectes maculatus
Ammodytes americanus
Anguilla rostrata
Membras martinica
Menidia beryllina
Menidia menidia
Opsanus tau
Scomberesox saurus
Strongylura marina
Tylosurus acus
Caranx crysos
Caranx hippos
Caranx latus
Selene vomer
Trachinotus carolinus
Trachinotus falcatus
Trachinotus goodei
Chaetodon ocellatus
Alosa aestivalis
Alosa mediocris
Alosa pseudoharengus
Alosa sapidissima
Brevoortia tyrannus
Clupea harengus
Sardinella aurita
Conger oceanicus
Myoxocephalus aenaeus
Myoxocephalus scorpius
Cyclopterus lumpus
Liparis atlanticus
Symphurus plagiusa
Notropis bifrenatus
Ecological
Type
Vertical
Distribution
ER
ER
DA
ER
ER
ER
ER
MS
EM
MS
MM
MM
MM
MM
MM
MM
MM
ER
DA
DA
DA
DA
MM
MM
MM
MM
ER
MM
MM
EM
MM
FS
D
D
D
P
P
P
D
P
P
P
P
P
P
D
P
P
P
D
P
P
P
P
P
P
P
D
D
D
D
D
D
D
Functional Guild Types
Reproductive
Egg
Type
Dispersal
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
P
D
P
D
D
D
D
P
D
D
P
P
P
P
P
P
P
P
P
D
P
P
P
D
P
P
D
D
D
D
P
D
Residency
Maturity
SP
O, SP
O,R
R
O, SP
SP, R
R
*
O, SP
*
*
O
*
O
SP
*
*
*
O, SP
*
O, SP
O
SP
O, SP
*
*
O, SP
O, SP
O, SP
WP
SP
O
*
J/A
J, A, J/A
*
J/A
J/A
J/A
*
J, J/A
*
*
J
*
J
*
*
*
*
J
J
J
J
J, J/A
J
J
J
J, J/A
J
J
J/A
J
*
116
117
Table 3.3 (cont’d): Functional guild classification for each species encountered in the 15 nearshore areas examined.
Family
Cyprinidae
Cyprinodontidae
Diodontidae
Elopidae
Engraulidae
Ephippidae
Fistulariidae
Fundulidae
Gadidae
Gasterosteidae
Gerreidae
Gobiesocidae
Gobiidae
Hemiramphidae
Hemitripteridae
Labridae
Species
Notropis heterolepis
Cyprinodon variegatus
Chilomycterus schoepfii
Elops saurus
Anchoa hepsetus
Anchoa mitchilli
Chaetodipterus faber
Fistularia tabacaria
Fundulus diaphanus
Fundulus heteroclitus
Fundulus majalis
Lucania parva
Enchelypous cimbrius
Gadus morhua
Gadus ogac
Microgadus tomcod
Pollachius virens
Urophycis chuss
Urophycis tenuis
Apeltes quadracus
Gasterosteus aculeatus
Gasterosteus wheatlandi
Pungitius pungitius
Eucinostomus argenteus
Gobiesox strumosus
Ctenogobius boleosoma
Evorthodus lyricus
Gobiosoma bosc
Hemiramphus brasiliensis
Hyporhamphus unifasciatus
Hemitripterus americanus
Tautoga onitis
Ecological
Type
Vertical
Distribution
FS
ER
ER
MM
EM
EM
ER
MM
FS
ER
ER
ER
MS
MM
MM
DA
MM
MS
MM
EM
DA
EM
FM
ER
ER
ER
ER
ER
MM
EM
MM
MM
D
D
D
P
P
P
P
D
D
D
D
P
D
D
D
D
D
D
D
D
P
P
D
P
D
D
D
D
P
P
D
P
Functional Guild Types
Reproductive
Egg
Type
Dispersal
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
D
D
P
P
P
P
P
P
P
D
D
D
P
P
D
D
P
P
P
D
D
D
D
P
D
D
D
D
P
P
D
P
Residency
Maturity
O
SP, R
*
O
O
O, SP
*
*
O
O, SP, R
SP, R
R
O
O, R
R
O, SP, R
O
O
O, SP
SP
O, SP, R
O, SP, R
O, R
SP
O
*
SP
O, SP
SP
*
O
SP
*
J/A
*
*
J, A
J, J/A
*
*
*
J/A
J/A
A
*
J
J
J/A
J
J
J
J/A
J/A
J/A
A
J
J
J/A
J
A, J/A
*
*
J
J
117
118
Table 3.3 (cont’d): Functional guild classification for each species encountered in the 15 nearshore areas examined.
Family
Labridae
Lutjanidae
Monacanthidae
Moronidae
Mugilidae
Nomeidae
Ophidiidae
Osmeridae
Paralichthyidae
Pholidae
Pleuronectidae
Poeciliidae
Pomatomidae
Rachycentridae
Rajidae
Sciaenidae
Scophthalmidae
Serranidae
Species
Tautogolabrus adspersus
Lutjanus griseus
Aluterus schoepfii
Stephanolepis hispidus
Morone americana
Mugil cephalus
Mugil curema
Psenes sp.
Ophidion marginatum
Mallotus villosus
Osmerus mordax
Paralichthys dentatus
Paralichthys squamilentus
Pholis gunnellus
Limanda ferruginea
Pleuronectes putnami
Pseudopleuronectes
americanus
Gambusia affinis
Pomatomus saltatrix
Rachycentron canadum
Amblyraja radiata
Bairdiella chrysoura
Cynoscion nebulosus
Cynoscion regalis
Leiostomus xanthurus
Menticirrhus littoralis
Menticirrhus saxatilis
Micropogonias undulatus
Sciaenops ocellatus
Scophthalmus aquosus
Centropristis striata
Functional Guild Types
Reproductive
Egg
Type
Dispersal
Ecological
Type
Vertical
Distribution
MM
MM
MM
MM
FM
MM
MM
MS
ER
EM
DA
MM
MM
ER
MS
ER
D
P
D
D
P
P
P
P
D
P
P
D
D
D
D
D
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
MM
FM
MM
MM
MS
MM
ER
ER
MM
MM
MM
MM
ER
MM
MM
D
D
P
D
D
D
D
D
D
D
D
D
D
D
D
O
V
O
O
O
O
O
O
O
O
O
O
O
O
O
Residency
Maturity
P
P
D
D
D
P
P
P
P
D
D
P
P
D
P
D
O, SP
*
*
*
SP
O, SP
SP, R
*
*
SP
O, SP, R
O
*
O, SP
O
O
J, J/A
J
*
J
*
J
J
*
*
J/A
A, J/A
J
*
J/A
A
*
D
NA
P
P
D
P
P
P
P
D
P
P
P
P
P
O, SP, R
SP
O
*
O
O
O
*
SP
SP
SP
O
O, SP
O
O
J, J/A
J/A
J
J
A
J
J
*
J
*
*
J
J
J, J/A
J/A
118
119
Table 3.3 (cont’d): Functional guild classification for each species encountered in the 15 nearshore areas examined.
Family
Species
Ecological
Type
Sparidae
Stenotomus chrysops
Lagodon rhomboides
Sphyraenidae
Sphyraena borealis
Stichaeidae
Ulvaria subbifurcata
Stromateidae
Peprilus triacanthus
Syngnathidae
Syngnathus floridae
Syngnathus fuscus
Syngnathus louisianae
Synodontidae
Synodus foetens
Tetraodontidae Sphoeroides maculatus
Triakidae
Mustelus canis
Triglidae
Prionotus carolinus
Prionotus evolans
Prionotus tribulus
Uranoscopidae Astroscopus guttatus
* insufficient data for classification
MM
MM
MM
MM
MM
ER
ER
ER
MM
ER
MM
MM
MM
MM
EM
Functional Guild Types
Vertical
Reproductive
Egg
Distribution
Type
Dispersal
D
D
P
D
P
D
D
D
D
D
D
D
D
D
D
O
O
O
O
O
W
W
W
O
O
V
O
O
O
O
P
P
P
D
P
NA
NA
NA
P
D
NA
P
P
P
P
Residency
Maturity
O
O
O
O
*
*
O, SP
*
O
O, SP
*
O
O
*
*
*
J
J
J/A
J/A
*
A, J/A
*
J
J
J
*
J/A
*
*
119
120
Table 3.4: Proportional composition of functional guilds based upon species richness (S) and total catch (Ni) for fishes
examined in the NWA. See Methods for explanation of abbreviations.
Ecological
Type
MM:
MS:
ER:
EM:
FM:
FS:
DA:
Totals
S
0.464
0.064
0.264
0.082
0.027
0.027
0.073
1.000
Functional Guild Types
Reproductive
Egg
Type
Dispersal
Vertical
Distribution
Ni
0.058
0.000
0.881
0.024
0.013
0.000
0.024
1.000
P:
D:
S
0.364
0.636
Ni
0.770
0.230
1.000
1.000
V:
W:
O:
S
0.018
0.027
0.955
Ni
0.000
0.002
0.998
1.000
1.000
P:
D:
NA:
S
0.573
0.382
0.045
Ni
0.037
0.961
0.002
1.000
1.000
Residency
R:
SP:
WP:
O:
S
0.151
0.361
0.008
0.479
Ni
0.600
0.398
0.000
0.002
1.000
1.000
Maturity
J:
A:
J/A:
S
0.540
0.103
0.356
Ni
0.046
0.001
0.953
1.000
1.000
120
121
Table 3.5: Statistical results of linear regressions used to examine latitudinal variation of
functional guilds with respect to contributions made by species and individuals. n
indicates the number of sites available for comparison. Statically significant slopes (p
< 0.05) indicated in bold.
Guild
r2
Species
m
p
r2
Individuals
m
p
0.232
0.055
0.242
0.001
0.043
0.006
0.546
-0.019
0.002
-0.012
0.000
0.002
0.000
0.027
0.069
0.401
0.063
0.899
0.457
0.788
0.002
0.557
0.004
0.005
0.001
0.013
0.011
0.452
-0.055
0.000
0.005
-0.001
0.002
0.000
0.048
0.001
0.817
0.810
0.900
0.690
0.713
0.006
Vertical Distribution
P
15
0.072
D
15
0.072
-0.006
0.006
0.333
0.333
0.224
0.224
0.030
-0.030
0.075
0.075
Reproductive Type
V
15
0.151
W
15
0.014
O
15
0.076
-0.001
-0.001
0.002
0.152
0.671
0.320
0.122
0.112
0.166
0.000
-0.002
0.002
0.202
0.223
0.132
n
Ecological Type
MM
15
MS
15
ER
15
EM
15
FM
15
FS
15
DA
15
Egg Dispersal
P
15
D
15
15
Residency
R
9
SP
9
WP
9
O
9
0.881
0.881
-0.044
0.044
<0.001
<0.001
0.624
0.624
-0.040
0.040
<0.001
<0.001
0.020
0.546
0.250
0.054
0.003
-0.013
0.003
0.007
0.714
0.023
0.171
0.547
0.093
0.113
0.250
0.060
0.024
-0.026
0.000
0.002
0.425
0.378
0.171
0.525
Maturity
J
A
J/A
0.148
0.310
0.008
-0.014
0.011
0.003
0.394
0.195
0.852
0.314
0.173
0.320
-0.022
0.000
0.022
0.190
0.354
0.186
7
7
7
122
Figure 3.1: Location of nearshore studies used in large scale comparison. Biogeographic
provinces identified by dashed lines and italics.
123
60
Taxonomic Groups
50
40
30
20
10
0
50
48
46
44
42
40
38
36
34
Latitude (°N)
Figure 3.2: Number of species (closed dots, solid trend line r2: 0.954) and families (open
dots, dashed trend line r2: 0.970) encountered in nearshore collections
throughout the northwest Atlantic in relation to latitude. Cape Cod also
indicated (dotted grey line).
124
Figure 3.3: Percent similarity of 15 nearshore areas examined in the northwest Atlantic based on family data as indicated by the BrayCurtis index using a binary matrix. Zoogeographic provinces listed (Briggs 1974). See Table 3.1 for site details.
124
125
Figure 3.4: Percent similarity of 15 nearshore areas examined in the northwest Atlantic based on species data as indicated by the BrayCurtis index using a binary matrix. Zoogeographic provinces listed (Briggs 1974).See Table 3.1 for site details.
125
126
1.0
0.8
MM
r2: 0.232
MS
r2: 0.055
ER
2
r : 0.242
EM
r2: 0.001
FM
r2: 0.043
FS
r2: 0.006
0.6
0.4
0.2
0.0
Proportion of Species
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
1.0
DA
r2: 0.546
0.8
50
48
46
44
42
40
38
36
34
0.6
0.4
0.2
0.0
50
48
46
44
42
40
38
36
34
Latitude (°N)
Figure 3.5: Proportion of species and individuals exhibiting specific ecological types
across latitude. See text for guild definitions.
127
1.0
MM
2
r : 0.899
0.8
MS
2
r : 0.004
0.6
0.4
0.2
0.0
Proportion of Individuals
1.0
ER
r2: 0.941
0.8
EM
2
r : 0.001
0.6
0.4
0.2
0.0
1.0
FM
2
r : 0.013
0.8
FS
r2: 0.011
0.6
0.4
0.2
0.0
1.0
DA
r2: 0.916
0.8
50
48
46
44
42
40
38
36
34
0.6
0.4
0.2
0.0
50
48
46
44
42
40
38
36
34
Latitude (°N)
Figure 3.5 (cont’d): Proportion of species and individuals exhibiting specific ecological
types across latitude. See text for guild definitions.
128
Proportion of Species
1.0
0.8
P
r2: 0.072
D D
r2: 0.072
P
r2: 0.224
D
r2: 0.224
0.6
0.4
0.2
0.0
Proportion of Individuals
1.0
0.8
0.6
0.4
0.2
0.0
50
48
46
44
42
40
38
36
34 50
48
46
44
42
40
38
36
34
Latitude (°N)
Figure 3.6: Proportion of species and individuals exhibiting pelagic (P) or demersal (D)
vertical distributions across latitude. See text for guild definitions.
129
1.0
V
r2: 0.151
0.8
W
r2: 0.014
0.6
Proportion of Species
0.4
0.2
0.0
1.0
50
48
46
44
42
40
38
36
34
O
r2: 0.076
0.8
0.6
0.4
0.2
0.0
1.0
W
r2: 0.112
V
2
r : 0.122
0.8
0.6
Proportion of Individuals
0.4
0.2
0.0
1.0
50
O
r2: 0.166
0.8
48
46
44
42
40
38
36
34
0.6
0.4
0.2
0.0
50
48
46
44
42
40
38
36
34
Latitude (°N)
Figure 3.7: Proportion of species and individuals exhibiting viviparous (V),
ovoviviparous (W) and oviparous (O) reproductive types across latitude. See
text for guild definitions.
130
Proportion of Species
1.0
0.8
P
r2: 0.881
D
r2: 0.881
P
r2: 0.851
D
r2: 0.990
0.6
0.4
0.2
0.0
Proportion of Individuals
1.0
0.8
0.6
0.4
0.2
0.0
50
48
46
44
42
40
38
36
34 50
48
46
44
42
40
38
36
34
Latitude (°N)
Figure 3.8: Proportion of species and individuals exhibiting pelagic (P) or demersal (D)
egg dispersals across latitude. See text for guild definitions.
131
1.0
SP
r2: 0.546
R
r2: 0.020
0.8
0.6
Proportion of Species
0.4
0.2
0.0
1.0
0.8
WP
r2: 0.250
O
r2: 0.054
R
r2: 0.093
SP
r2: 0.113
WP
r2: 0.250
O
r2: 0.060
0.6
0.4
0.2
0.0
1.0
0.8
0.6
Proportion of Individuals
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
50
48
46
44
42
40
38
36
34 50
48
46
44
42
40
38
36
34
Latitude (°N)
Figure 3.9: Proportion of species and individuals exhibiting regular (R), summer
periodic (SP), winter periodic (WP) and occasional (O) residency types across
latitude. See text for guild definitions.
132
1.0
J
r2: 0.148
0.8
A
r2: 0.310
0.6
Proportion of Species
0.4
0.2
0.0
1.0
50
J/A
r : 0.008
48
46
44
42
40
38
36
34
2
0.8
0.6
0.4
0.2
0.0
1.0
A
r2: 0.173
J
r2: 0.314
0.8
0.6
Proportion of Individuals
0.4
0.2
0.0
50
1.0
48
46
44
42
40
38
36
34
J/A
r2: 0.320
0.8
0.6
0.4
0.2
0.0
50
48
46
44
42
40
38
36
34
Latitude (°N)
Figure 3.10: Proportion of species and individuals exhibiting juvenile (J), adult (A) and
mixed (J/A) maturity types across latitude. See text for guild definitions.
133
3.7
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136
4 CHAPTER 4: GENERAL SUMMARY AND CONCLUSIONS
137
4.1
Summary
There were two main objectives to this investigation. The first objective was to
assess temporal and spatial variation in the nearshore fish assemblage structure of an
under-described portion of the Canadian Atlantic; the southwest Bay of Fundy. The
second objective was to use this data in conjunction with existing nearshore records
from throughout the NWA and conduct a meta-analysis in order to identify prevailing
trends in taxonomic and functional guild structure over a large geographic area;
Newfoundland (47° 38' N) to Cape Hatteras (35° 13' N).
4.1.1 Southwest Bay of Fundy Nearshore Fish Assemblage
Four aspects of assemblage structure were examined in the southwest Bay of
Fundy: a) temporal variability at seasonal and b) tidal/diel scales; c) spatial variability
throughout the region and; d) the identification of prevalent ecological characteristics
through the use of functional guilds. Significant sources of spatial and temporal variation
were identified in the fish assemblage structure of the southwest Bay of Fundy at each of
the seasonal, tidal/diel and regional scales examined. At a seasonal scale the assemblage
consisted of 18 species and exhibited a high degree of dominance. Seven species
accounted for 96.18% of the total catch with M. menidia comprising 53.95%, O. mordax
18.70%, C. harengus 9.25%, P. americanus 3.86%, M. tomcod 3.86%, M. scorpius
3.30%, and G. wheatlandi 3.26%. This degree of dominance appears to be typical of the
region and comparable patterns were also observed in the Gulf of Maine by Ayvazian et
al. (1992), Lazzari et al. (1999), Able et al. (2002), and Wilbur (2004). Most species
occurring in the assemblage were demersal fishes of marine origin and were derived
138
from pelagic eggs. These fishes primarily utilized the nearshore area periodically
throughout the warmer months of the year (May – December), largely as a nursery
ground.
At the scale of months species richness and abundance were strongly correlated
with water temperature but not salinity, exhibiting highs from June through October (S >
8, Ni > 400) and lows December through April (S < 4, Ni < 200). These observations are
typical of temperate fish assemblages and are consistent with previous findings on
seasonal variation conducted by Lazzari et al. (1999), Methven et al. (2001) and Able et
al. (2002) throughout the northwest Atlantic.
Considerable variation in assemblage structure was also observed at a 24 hour
scale as species richness and abundance were largely influenced by the tide and time of
day. The greatest values for species richness and abundance were observed during low
tide, while peaks in abundance occurred at twilight. These results were comparable to
previous studies which examined 24 hour variability of nearshore fish assemblages in
Scotland (Gibson et al. 1996) and South Africa (Lasiak 1984).
Spatial variability at the scale of sites within the southwest Bay of Fundy
assemblage was largely influenced by substrate type with more structurally complex
substrates such as gravel and rock supporting assemblages with greater species richness
and abundance than soft substrates such as sand and mud. However spatial proximity
among sites had little direct influence on the assemblage structure observed. Habitat type
was also identified as the driving factor influencing assemblage composition by Lazzari
and Tupper (2001) in the Gulf of Maine.
139
Overall, variation in the nearshore fish assemblage of the southwest Bay of
Fundy was influenced by several physical and biological factors operating at multiple
spatial and temporal scales. These processes have direct implications for the
management of nearshore regions and must be considered when designing sampling
protocols for monitoring finfish in order to minimize natural variation in assemblage
structure as well as adequately assess patterns and processes responsible for finfish
variance.
4.1.2 Northwest Atlantic
The taxonomic structure of the nearshore fish assemblage in the NWA was
consistent with previous observations made for coastal fishes of the region. Findings
supported the biogeographic provinces proposed by Briggs (1974, Labrador, Acadian,
Virginian) with the exception of the northern portion of the Virginian province which
exhibited elevated richness due to its location in a transition area for nearshore fishes,
subsequently supporting species from each of the Acadian and Virginian provinces.
With respect to functional guild structure, NWA nearshore fish assemblages
supported unique guild structures depending on whether the proportion of species or
their relative abundance was examined. In terms of species composition the NWA
assemblage was largely dominated by marine migrants (MM: 46.4%). The majority of
these fishes were demersal (D: 63.6%), utilized an oviparous reproductive strategy
(95.5%) and produced pelagic eggs (P: 57.3%). These species occurred either
infrequently throughout the year or were limited to the warmer months (O: 47.9%, SP:
140
36.1%, May through December), occupying the nearshore area exclusively during the
juvenile stages (J: 54.0%).
Marked differences in guild structure were observed when this data was analyzed
to incorporate the relative abundance of each species. From this perspective the
nearshore assemblages were dominated by estuarine resident fishes (ER: 88.1%). The
majority of these individuals were also pelagic (77.0%) despite the overall prevalence of
demersal species. Also, while the oviparous reproductive type remained dominant (O:
99.8%), the majority of these individuals produced demersal eggs (D: 96.1%) and were
represented by members of both the juvenile and adult life history stages (95.3%).
Latitudinal gradients were also evident over the range of studies examined (47°
38' N through 35° 13' N) with diadromous species being dominant in the northern
assemblages and marine migrant species dominating in southern areas. A progressive
change in egg dispersal was also observed with demersal eggs being replaced by pelagic
eggs from north to south. However further research will be required in order to identify
the processes responsible for these trends.
4.2
Conclusions
4.2.1 Functional Guilds
The functional guild approach has been proven to be a valuable tool for
describing the ecological structure of finfish assemblages (Elliott and DeWailly 1995,
Whitfield et al. 1999, Mathieson et al. 2000, Thiel et al. 2003). However the suitability
of the functional guild approach for making large scale comparisons is currently limited
141
by inconsistent terminology among studies as well as inadequate biological information
for many species. Due to the inherent flexibility of functional guilds in describing
ecological traits (Brown 2004), considerable variation in terminology exists with
investigators often using different approaches to describe similar concepts (e.g.,
ecological type: Ayvazian et al. 1992, Elliott and DeWailly 1995, Whitfield et al. 1999,
Nordlie 2003). Due to the fact these approaches are rarely standardized, comparisons
between studies is often impractical without reanalyzing data.
These inconsistencies also extend to the functional guild concept itself, as
multiple synonyms are currently used throughout ecological research (e.g., ‘species
traits’, functional traits’, and ‘ecological guilds’ discussed in Wilson 1999) and as a
consequence the existing body of literature is largely unorganized impeding accurate
reviews of existing information. In order to facilitate future comparisons the adoption of
a standardized approach will be necessary for finfish (Whitfield et al. 1999, Elliott
2002).
A second obstacle for large scale analyses regards the quality of data currently
available for accurate species classification. As discussed by Elliott and DeWailly
(1995) the functional guild approach has a fundamental difficulty given that the biology
of even common species has not been thoroughly documented, and as a consequence
classifications are at times based on assumptions, unconfirmed reports or characteristics
of closely related species. As a result reliability of species classifications are difficult to
assess due to potential misclassification and as a consequence species designations must
be viewed critically throughout the functional guild literature.
142
4.2.2 Implications for Management of Nearshore Areas
Physical and biological processes operating at multiple spatial and temporal
scales introduce natural variability into an ecosystem and have considerable influence on
the fish assemblage structure observed in nearshore environments. As a consequence, it
is important to consider spatiotemporal variation when designing sampling protocols for
monitoring these species. Otherwise natural processes may introduce sources of
variation which confound accurate interpretation of the results. Based on the findings of
this study the optimal time and place to sample in the southwest Bay of Fundy while
maintaining the highest levels of richness and abundance is to sample at sites with
complex substrates (e.g., gravel, algal coverage), at low tide, throughout the warmest
months of the year (May – December). Sampling during alternate periods may
underestimate the species richness and abundance of the fish assemblage (Stoner 1991).
4.2.3 Future Research
As monitoring of finfish assemblages continues to become an integral part of
environmental and fisheries research, further study will be required to determine how
marine nearshore fish assemblages are influenced by anthropogenic effects as well as
identifying patterns and processes responsible for temporal variation at scales of decades
and centuries.
The effects of contaminants on fish assemblage structure and ecosystem health
has received considerable attention in freshwater ecosystems (Munkittrick 2000);
however comparably little information exists regarding how these factor alter estuarine
and marine assemblages. Current research in marine environments has largely focused
143
on natural processes known to influence fish community structure such as temperature
and salinity (e.g., Haedrich 1983, Methven et al. 2001). Meanwhile our understanding of
the influence factors such as toxic substances, oxygen content and light intensity have on
community structure remains limited despite the considerable influence these parameters
potentially have on the value of specific habitats to fishes (Ryder and Kerr 1989, Peters
and Cross 1992).
A second area of interest for future research will be identifying the processes
responsible for natural variability in nearshore finfish communities over large temporal
scales. Due to the fact humans perceive time on a diel to annual time frame, research
often lacks perspective beyond these scales. As a consequence nearshore research to date
has largely focused on spatiotemporal variability throughout the course of one or two
years. However evidence has shown that these communities operate in response to
processes operating at scales of decades to centuries where the number of standardized
data sets available is greatly reduced. In order to detect long term changes in assemblage
structure future research will require a long-term perspective which will permit
delineation between natural and anthropogenic induced changes (Lekve et al. 1999).
144
4.3
Literature Cited
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Mathieson, S., A. Cattrijsse, M.J. Costa, P. Drake, M. Elliott, J. Gardner, and J.
Marchand. 2000. Fish assemblages of European tidal marshes: a comparison based
on species, families and functional guilds. Marine Ecology Progress Series. 204:
225-242.
Methven, D.A., R.L. Haedrich, and G.A. Rose. 2001. The fish assemblage of a
Newfoundland estuary: Diel, monthly and annual variation. Estuarine, Coastal and
Shelf Sciences. 52: 669-687.
Munkittrick, K.R., M.E. McMaster, G. Van Der Kraak, C. Portt, W.N. Gibbons, A.
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cumulative effects assessment using fish populations: Moose River Project.
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estuary. Estuarine, Coastal and shelf Science. 33: 57-69.
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Fisheries and Aquatic Science. 105: 2–12.
Thiel, B.R., H. Cabral, and M.J. Costa. 2003. Composition, temporal changes and
ecological guild classification of the ichthyofaunas of large European estuaries – a
comparison between the Tagus (Portugal) and the Elbe (Germany). Journal of
Applied Ichthyology. 19: 330-342.
Whitfield, A.K. 1999. Ichthyofaunal assemblages in estuaries: A South African case
study. Reviews in Fish Biology and Fisheries. 9: 151-186.
Wilson, J.B. 1999. Guilds, functional types and ecological groups. Oikos. 86: 507-522.
VITA
Candidate’s full name: Collin James Arens
Universities attended:
University of New Brunswick, Saint John, NB
1999-2003
BSc (Honours) - Marine Biology
Publications:
Arens, C. J., and D. A. Methven. 2006. Tidal and diel variation in the nearshore fish
assemblage of the Musquash estuary, New Brunswick: Implications for
biomonitoring in a Marine Protected Area. Report to the Department of Fisheries
and Oceans, Project # F5305-05C060, March 2006. Canadian Rivers Institute,
Department of Biology, University of New Brunswick, Saint John, NB, Canada.
Casselman, J., Arens, C.J., Methven, D.A. and T. Vickers. 2005. The occurrence,
distribution and composition of fish community assemblages in the Saint John
Harbour. Atlantic Coastal Action Program, Saint John, N.B. Canada. Submitted to
Wildlife Trust Fund of the NB Wildlife Council.
Peters, L.E., Arens, C.J., Methven, D.A. and K.R. Munkittrick. 2004. Challenges for
developing monitoring programs in the Saint John Harbour, NB. EEM Science
Symposium 2004 and Canadian Rivers Institute Day, Fredericton New Brunswick,
February 16th -18th, 2004.
Casselman, J., Vickers, T., Methven, D.A. and C.J. Arens. 2003. Fish Community
Assemblages of the Saint John Harbour. Atlantic Coastal Action Program, Saint
John, N.B. Canada. Submitted to Wildlife Trust Fund of the NB Wildlife Council.
Conference Presentations:
Arens, C.J., Methven, D.A. and K.R. Munkittrick. Seasonal and Regional Variation in
the Nearshore Fish Assemblage of the Southwest Bay of Fundy. Platform
presentation at the 7th Bay of Fundy Ecosystem Partnership Conference. St.
Andrews, NB, Canada. October 25-27, 2006.
Arens, C.J., Methven, D.A. and K.R. Munkittrick. Seasonal and Regional Variation in
the Nearshore Fish Assemblage of the Southwest Bay of Fundy. Poster
presentation at the Canadian Water Network Annual Meeting, Fredericton, NB,
Canada. March 6-8, 2006. Atlantic Coastal and Estuarine Science Society
Conference and Canadian Rivers Institute Day, University of New Brunswick,
Fredericton, NB, Canada. May 16-18, 2006.
Methven, D.A., Peters, L.E., and C.J. Arens. Structure of the nearshore fish assemblage
in the lower Bay of Fundy: short-term variability and implications for sampling
design. Platform presentation at the 6th Bay of Fundy Ecosystem Partnership
Conference. Cornwallis, NS, Canada. September 29-October 2, 2004.
Arens, C.J. Nearshore fish community structure in the southern Bay of Fundy. Platform
presentation at the Canadian Society of Zoologists Conference. Acadia University,
Wolfville, NS, Canada. May 11-15, 2004.
Arens, C.J., and D.A. Methven. Influence of declining demersal fish populations on
abundance and distribution of pelagic larvae: white hake in the southern Gulf of St.
Lawrence. Poster presentation at the Canadian Society of Zoologists Conference.
Acadia University, Wolfville, NS, Canada. May 11-15, 2004.
Peters, L.E., Arens, C.J., and D.A. Methven. Diel and seasonal variation in nearshore
fish assemblages: implications for EEM design. Poster presentation at the
Environmental Effects Monitoring Science Symposium. University of New
Brunswick, Fredericton, NB, Canada. February 16-18, 2004.
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