1982 Shellfish Management Advice, Pacific Region

1982 Shellfish Management Advice, Pacific Region
1982 Shellfish Management Advice,
Pacific Region
G. S. Jamieson (Editor)
Department of Fisheries and Oceans
Fisheries Research Branch
Pacific Biological Station
Nanaimo, British Columbia V9R 5K6
August 1984
Canadian Manuscript Report of
Fisheries and Aquatic Sciences
No. 1774
~.
• <
.
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Canadian Manuscript Report of
Fisheries and Aquatic Sciences 1774
August 1984
1982 SHELLF ISH MANAGEMENT ADVICE. PAC IF IC REGiON
by
G. S. Jamieson (Editor)
Department of Fisheries and Cteans
Fi sheries Research Branch
Pacific Biological Station
Nanaimo, British Columbia
V9R 51<.6
- ii -
(cj Minister of Supply and Services Canada 1984
Cat. No. Fs97-4/1774E
ISSN 0706-6473
Correct citation for this publication:
Jamieson, G. S. (Editor) ..
Re9ion.
1984.
1982 Shellfish Management Advice. Pacific
Can. MS Rep. Fish. Aquat. Sci. 1774:
71 p.
- ii 1
TABLE OF CONTENTS
Introduction
1
Biomass, Year-Class Abundance, and Distribution of Pink Shrimp
J. Bouti 11 ier
2
Prawn - Minimum Size Limit
J. Bouti11ier
11
Sea Urchins: Suitability of the Present Minimum Size Limit
Paul A. Breen
25
Recanmendations for the 1983 Abalone Season
Paul A. Breen
53
Observations of the B.C. Sea Otter Transplant
Paul A. Breen
57
Scallop Size Limits
Neil Bourne
67
- iv ABSTRACT
Jamieson. G. S. (Editor). 1984. 1982 Shell fi sh Management Mvice, Pacific
Region. Can. MS Rep. Fish. Aquat. SCi. 1774: 71 p.
Biological advice given to resource managers by staff of the
Shellfish section in December. 1982 is presented as a series of docllJlents.
Topics discussed include the status of abalone (Haliotis kamtschatkana) and
pink shrimp (Pandalus jordani) stocks; minimum size limits reccmnendations for
praMns (f.. platyceros), sea urchins (Stronglyocentrotus franciscanus), and
scallops (patlno~ecten caurinus, Chlamys rubida and C. hastata)j and
observations onritlsh COlumbia sea otter (Enhydra Tatrls) abundance.
RESLI1E
Jamieson. G. S. (Editor). 1984. g,ellfish Management Pdvice, Pacific
Region. Can. MS Rep. Fi sh. Aquat. SCi. 1774: 71 p.
Les conseils biologiques donnes, en decembre 1982, aux gestionnaires
des ressources par le personnel de la section des moll usques et crustaces sont
presentes CCJmle une serie de docl.lJ\ents. Les sujets traites canprennent 1a
situation des stocks d'ormeau (Haliotis kamtschatkana) et de crevette
oceanique (Pandalus jordani). les recarmandations sur la taille legale
minimale de 1a crevette tachee (P. platyceros). de lloursin
(Stronglyocentrotus fransciscanus) et des petoncles (Patinopecten caurinus,
Chlamys rubida et
hastata) et des observations sur 1'abondance de 1a 10utre
marine (["hydra latris) en COlanbie-Britannique.
c.
INTROOUCTlON
The Fisheries Research Branch in the Pacific Kegion provides
biological ana scientific advice for managing, protecting.
an~
developing the
region's freshwater and marine resources.
It consists of a number of
sections. one of which is the ~hel1fish ~ection. and speciflc functions and
areas of responsibil ity of this section are as follows:
1.
to undertake research on the distribution. life history. ecology.
physiology. and behavior of conrnercial and potentially commercial
invertebrate and
n~rine
plant species;
2.
to carry out resource surveys and the sampling of commercial catches
tor stock assessments of invertebrate ana n~r;ne plant species;
::so
to participate in research on the impact of natural and man-induceo
factors on the habitat of invertebrate aM marine plant stock.s;
4.
to maintain fishery oata bases and to develop analytical methods.
including the use of theoretical oodels, to achieve the
!).
above~
to provi de bi 01 ogi cal management advi ce to the management bi 01ogi sts
-and senior management, and to corrmunicate research results to
fishermen. inaustry. ana the scientific community.
This collection of manuscript oocunlents is the scientific basis for shellfish
fisheries management advice given in December, lYb~ by the Fisheries ResearCh
~ranch in the Pacific region.
As such these oocuments adaress the issues of
the day in the tire frames required and are not intended as oefinitive
statements on the subJects addressed. kather. they should De consiaered as
progress reports all ongoing investigations.
- 2 -
biOMASS, YEAR-CLASS ABUNUANCE, ANO UISTRIBUTION UF PINK SHRIMP
by
J. l:!outi11ier
Department of Fisheries and Oceans
Fisheries Research Branch
Pacific Biological Station
Nanaimo, B.C. V~R ;K6
A.
INTRUDUCTION
This aocument summarizes the data collected on the May
19~2
b.B. REED shrilJll biomass survey of shrill4J grounds off Tofino. Nootka Sound and
in Queen Charlotte Sound. The survey was designed to collect data for
estimating the total biomass. year-class abundance. and distributions of the
smooth pink shrimp. Pandalus Jordani. In addition to the trawl survey.
oceanographic temperature observatlons were collected.
B.
METHODS
The oiomass trawl survey was carried out in all three areas using a
standard bl-ft. high-rising. N.M.F .5. shrimp sampling trawl. This traWling
gear has been oescribed in detail. The temperature observations were made
using expendable bathythermographs (XBTs).
The trawl locations for the biomass of Tofino and Nootka grounds
were established on a systematic grid pattern based on loran C blocks. Tows
were made di agonally throu!1l adjacent !>~9D-X blocks along 5~~D-Y 1i nes.
Successive 5990-Y lines were lU microseconds apart. The trawl locations for
the Queen Charlotte Sound biomass survey were made on a loran C grid in which
tows were made diagonally through !)~90-X blocks 2V microseconos apart along
successive :J!::l!::lU-Y lines IS microseconds apart. Variations in the grid
patterns occurred when exploring new areas, avoiding bad bbttom. or oeing set
off by the ti de and wi no.
-
3 -
Tows lasted 3U min and covered a range of distances from 1.2-l.Y M.
Upon completion of each tow, the large fish were removed from the
invertebrates, and small fish was put into tuns and weighed. Une tub was then
sorted into shrilTl' and scrap. the percentage of Shrimp by weight per tub was
determined, and the total shrimp catch for the tow was then extrapolated.
Random samples of shrimp were weiyhed and the number of snrimp per kilogram
determined. The samples were then sexed and measured and the information
obtained was used to determine the various year-class strengths.
The biomass for each area was calculated by using a planimeter to
measure the aredS of concentration in square nautical miles. This area was
then ITlJltipl ied IJy the mean catch per nautical mile towed and the nunber of
tows required to sweep a square nautical mile using the NMFS shrimp survey
trawl (174). The 95% confidence levels on the estimated biomasses for the
different areas were calculated by assuming a normal distribution within any
concentration. This assumption may not be correct and further calculations on
transformed data will be calculated at a later date.
C.
,
RESULTS
Total catch (kg) by sper.ies for the west coast of Vancouver Island
(Tofino and Nootka grounds) and ~ueen Charlotte Sound is given in Tables 1 and
2~ respectively.
1.
Tofino ground
The Tofino shrimp ground is a fishing area which lies offshore of
the west coast of Vancouver Island oetween 48"4U' and 49"15 1 • The
concentration of shrimp for this survey was found to be distributed in four
concentr at ion s.
The major area of concentration was a 27 M2 area located in the
southern portion of the ground from Loran C 599U-Y-29145 and 5Y9U-Y-29205
between 68 and 82 fathoms. The catch rates in this area ranged from 7 to 653
kg per half -hour towed.
The next major concentration was found in a 16 M2 located in the
northern portion of the yround from Loran C 5990-Y-29285 to 599U-Y-29325
between 67 and 79 fathoms.
kg per half-hour towed.
The catch rates in this area ranged frOOI 11 to 180
The remaining two concentrations of Shrimp were both small 5 M2
areas located at the southern and northern extremes of the ground. The catCh
rates for the southern and northern areas averaged 3 and 15 kg half-hour
towed, respectively.
- 4 -
The total cOlTDined snrimp biomass for all four areas was estimated
at 813 metric tonnes which is only 53% of the 1982 estimated biomass. Within
these areas the shrimp ranged in size from 153 to 476 shrimp per kilogram with
a weighted mean count of 195 shrilllJ per k.ilogram.
At the 95% confidence level the biomass estimate ranged from 0 to
1,108 M.
2.
Nootka ground
The Nootka ground is a. fishing area which lies offshore off the west
coast of Vancouver Island between 49"15 1 and 49.35 1 • During this survey the
shrimp were only located in one 26 M2 area in the central portion of the
9round from Loran C 5990-Y-29465 to 599U-Y-29525 between 68 and 77 fathoms.
The estimated biomass for the shrimp concentration in this area was
171 Mwhich was on 12% of the 1981 estimated biomass. Within this area the
shrimp ranged in size from 166 to 264 shrilTl> per k.i1ogrOO1 with a weighted mean
count of 246 shrimp per k.ilogram.
At the 95~ confidence level the biomass estimate ranged from 0 to
398 metric tonnes.
-
5 -
Table 1. The total catch for the survey off the west coast of Vancouver
Island (Tofino and Nootka grounds) su~narized by important species.
Total number of haul s
Species
Pink (Jordan;)
5un starfish
Hrittle stars
Sea urchins
Heart urchin
= ~,
Percent
Kg
1612.
1.
Sea cucumber
liox r.r ab
8.
3.
4.
36.
3.
Dab (Pacific)
41.
Uover sole
English sole
Flathead sole
Halibut
30.
8.
426.
68.
Y.
80.
Petrale sole
Rex sole
Slender sole
Turbot
Rockfish
S. borealis
'S. brevlsplnis
"5. cramen
"5'. elongatu5
S. f1 avidus
'5'. pauclsp,nis
S. pinniger
"5'. pronger
'"5".
rubernmus
"5'. zacentrus
irl ackcod
Cymatogaster
Eulachon
Hake
Herring
Lingcod
Pacific cod
Walleye pollock
Sc:ulpins
Shad
Tomcod
Dogfish
Ratfi sh
Skates
gg.
105.
37.
2.
34.
31.
5.
49.
278.
185.
14.
10.
12.
29.
5.
2602.
4.
76.
848.
89.
279.
1.
4.
137.
3046.
1.
26.
15.58
0.u1
0.08
0.03
0.U4
0.35
0.U3
0.4U
0.2Y
0.08
4.12
U.66
O.Og
U.77
0.96
1.01
0.36
0.02
0.33
0.30
0.05
0.47
2.6Y
1. 79
0.14
0.10
U.12
0.28
0.U5
25.15
0.04
0.73
8.20
0.86
2.70
U.01
0.U4
1.32
2Y.44
0.01
0.25
- 6 -
3.
Queen Charlotte Sound
The survey in Queen Charlotte Sound was conducted in the N.E. and
N.W. corners of the Goose Island grounds. Shrimp were caught in 7 of the 10
tows made in the N.E. corner grounds with the catch rates varying from 2 to 46
kg per half-hour towed. Shrimp were caught in 5 of the 7 tows made in the
N.W. corner grounds with the catch rates varying from 4 to 13 kg per half-hour
towed. The shrimp counts ranged frOOl 182-250 shrimp per kilogram with the
entire area having a weighted mean count of 222 shrimp per kilogram. In
cOOlparing the size of shrimp frOOl this survey with the rrean count of 312
shrimp per kg in the 1981 survey, it can at first glance be speculated that
there ;s a paucity of juvenile shrimp in the catches of this year's survey.
Biomass estimates were not attempted for these grounds since time
constraints prevented conducting sufficient survey trawls to delineate the
total area of shrimp concentrations. A non-parametric Mann-Whitney U test was
carried out comparing the 1982 tows (nulTber of shrimp per Mtowed) with the
1981 and 1980 tows for both the N.E. and N.W. corners of the Goose Island
grounds. The results of the tests indicate that the catch rates for the N.E.
Goose Island grounds have not changed significantly over the last three
surveys, but that the catch rates for the N.W. grounds were significantly
hi9her (at a 0.05 level of si9nificance) in 1981 than in either the 1982 or
1980. The comparison between 1982 and 1980 catch rates for the N.W. 9rounds
showed no significant change.
Table 2. The total catch for the survey in Queen Charlotte Sound
summarized by important species.
Total nunber of hauls
Species
Pink (Jordan;)
Sidestr;pe
Sponges
Gonatus magister
Heart urch i n
Sea cucumber
Dover sole
English sole
Flathead sole
Halibut
Turbot
Rockfish
S. aleutianus
S. alutus
"5. babcock. i
S. brev;spinis
S. entomelas
,. flavidus
helvomaculatus
S. pinniger
,.
=
17.
K9
Percent
133.
1.
6.
1.
5.47
0.04
0.25
0.04
0.04
0.29
2.88
0.04
1.03
2.26
36.51
0.16
0.25
23.56
1.85
0.45
0.04
0.33
0.04
0.25
l.
7.
70.
1.
25.
55.
888.
4.
6.
573.
45.
11.
1.
8.
1.
6.
-
7 -
Cont'd
Kg
Percent
51.
5.
92.
46.
8.
44.
4.
7.
292.
15.
25.
2.W
0.21
3.78
1.89
0.33
1.81
0.16
0.2Y
12.01
0.62
Species
S. proriger
'5"eb. alascanus
"B"T"ic k cod
Eulachan
Herring
Lingcod
Pacific cod
Wa 11 eye po 11 ock
Dogfish
katfi sh
Skates
O.
I.U3
DISCUSSION
system.
Generally the Tofino and Nootka fisheries are managed on a quota
In order to set precautionary total allowdole catches for the areas,
the estimated biomasses are applied to exponential yield at equilibrilJll
models.
mIn F
Ye =
B~
Fe
K
The result i 09 TACs are imp 1emented as of May 1 of the current year. wi th the
areas remaining open until the quota is taken or until May 1 of the following
year when new lACs are recorrmended.
For the Tofino grounds the 1982 stock assessment estimated the
biomass at -813 M which indicated a decline in virtual yrowth from the lY81
levels. Because of the low biomass estlmates the recomnended quota of 113
M was derived by applying a reconstructive strategy to an exponential model of
the grounds (Fig. 1). This reconstructive strategy only allowed for an
exploitation rate of approximately 4(1.\ of the yield at equilibrium
(-280 M). No quota was set for either the Nootka ground or l,Jueen Charlotte
Sound as it was believed that it would be uneconomical to fish these areas.
These areas are to remain open to fishing as it was felt that any information
obtained from a corrmercial fiShery which might help explain the al-'parent
decline in stocks would be worth the risks of fishing on an apparently
uneconomical stock. To date any attempted f·ishery in the area has Il"et with an
apparent lack of success.
MSY
54
-;;; 45
'"cc
o
-'"
v
36
~
E
(82) Yield at equilibrium
o 27
><
'"
~
"0
>='"
18
I
I
0-1
'.
9
D
dJ (82)
9
Desirable aperatinll level for
reconstruction at proportion B
Bmax
I
I
I
I
,
I
I
I
18
27
36
45
54
63
72
81
Biomass (x 10 2 metric tonnes)
Ili~.
1.
Tofino Grounds exponential model yield at equilibrium.
-
-
11 -
PRAWN - MINIMUM SILE LfMIT
by
J. Boutil1ier
Uepartment of Fisheries and Oceans
Fisheries Research 8ranch
Pacific IHological Station
Nanaimo, B.C.
A.
V9R 5K6
INTRODUCTION
This document discusses the rationale for the adoption of a rnlnlmum
size limit for prawns (Pandalu5 platyceras) into the shellfish regulations.
~.
METHUDS
The analysis used in this document was Kicker's method of estimating
equl1ibrium yield per given recruit.
t=t
b
2
This method was chosen as it incorporates aye specific differences in growth
rates, natural mortality rate, rate of fishing; and it easily allows for
examination of varying fishing strategies such as different minimum size
limits. open and closed seasons, etc. Implicit in the use of this analysis is
that the situation hypothesized has been in effect long enough to allow the
population to establish an equilibrium condition.
The estimates of age specific growth rates, natural lllJrtality
rates, and availability to fishing mortality were obtained from a series of
- 12 -
research surveys carried out on the prawn stocks in Knight Kingcome Inlet.
No
estimate of an equilibrium F was available for this analysis because the
information from the commercial fishery is so poor.
c.
RESULTS
The results of the analysis are presented in two parts. The first
part will discuss estimates of realistic F values and the second part will
deal with a rMnipulation of age at first capture and the resulting yiela to
the fishery. An important part of the analysis to determine the benefits with
changing age at first capture. is the inclusion of a price differential of .7':J
for small 113-24 month) prawns to 3.UU for medium {2b-j6 month). and large
(37-4ti IOOnth) prawns. The initial analysis looked at the ronthly F max and
F u.\ for all cohorts combined with recruitment starting at 1J n(lnths. The
resu ts of this analysis gave a ITDnthly F U.l of .14 (Fig. 1). J\n important
cons i de rat i on that ari ses with a leve 1 of F as 1arge as th 1sis that these
animals are protandic hermaphrodites and only function as females in the final
year of life. This life nistory strategy necessitates that a certain
proportion of a cohort must be available to function as females at the til'l'e of
terminal spawning, i.e., the ~ roonth mark.. It is evident in Fig. l that at a
level of F>.14 there would be little if any female spawning biomass escaping.
It was felt that a IOOre realistic level of F could be obtained by adopting the
approach of estimating the F max and F 0.1 for a fishing strategy which
maximizes the yield from the 36+ IOOnth lndividuals. The results of this
analysis can be seen in Fig. 3A which indicates an F max of .ubl and an
F 0.1 of .041. These are IIUch rrore realistic levels of F as they still
allow for a female terminal spawning biomass.
For the purposes of the comparative portion of this analysis it will
be assumed that the levels of F max and F l).1 would still allow the
population to remain at equilibrium. In vrewing the resulting changes in
biomass when the population is unfished (Fig. 4) it is evident that the
maximum biomass of a cohort is obtained at the age of .!:tl rronths. Since the
nature of the fishery does not all~ for a knife edge harvesting strategy it
was felt that the roore beneficial strategy was to evaluate the results of
increasing the age of first capture from-13 months to 2!J months. The results
of the changing shape of the yield curve can be seen in Fig. 3b. From this
analysis it was evident that firstly the Fmax has increased and results in a
higher production from ~7+ month portion of the life history.
Table 1 shows the results of a comparison of the total Yleld and
economic return of the two F max (37+) and F 0.1 lJ7+) for the lJ-4l:S and
2!J-4~ month exploitation strategies.
1t is seen in Fig. bA that if F remains
constant the value of the catch is higher at al1Y monthly F>.Ot:tj. It is also
evident in Fig. 58 tnat for any constant F. a delay of the age at first
capture results in an increased spawning biomass.
-
O.
13 -
RECUMMENDATIUNS
It is evident from this analysis that at a monthly F>.02B an
increase in age of first capture will almost surely oenefit tne industry if
the assurnptions are correct about price differential~ growth rates. natural
mortality rates. and availability qualifiers. Even with a monthly F <.U2B
(Fig. SA) the benefits to the industry are not appreciaoly reduced by
increasing the age of first capture to 25 months. It is, tnerefore.
recorrmended that an increase in age of first capture would be a positive
reguhtion to institute. Using the growth rates from the Knight and Kingcome
Inlet study. increasing the age at first capture to 25 months would be
equivalent t6 putting a minimum size limit of 30.0 ITJn carapace length or lU6
mm (4.2 inches) in total length. as measured from the posterior margin of the
orbit of the eye to the tip of the telson When the prawn is fully extended but
not stretched. The problems that are inherent in this regulation are:
(1) the variability of growth rates between areas, (2) the release of
undersize prawns.
-
14 -
Table 1. Comparisons of the total yield and economic return of the two fishing
strategies F Max and F 0.1.
I
At F Max
Yield
F (13 to 48)
F Max = .051
1+
-1021.83
2+
1258.55
3+
545.74
Total
2826.12
Spawning biomass
266.60
Va 1ue * $6179.24
F (25 to 48)
Yield
F IViax = .066
1+
-02+ 1888.39
3+ 696.53
Total 2584.92
Spawning biomass
234.62
Value * $7754.76
+50%
+27.6%
-08.5%
-12.0%
+25.5%
*Values of the resource are based on a value of $.?0/pound for 1+ and
$3.00/pound for 2+ and 3+ animals.
At F 0.1 = .041 monthly
Age
(months)
Yield (13-48)
1+ 13-24
2+ 25-36
3+ 37-48
836.63
1104.15
533.31
Value
Spawning biomass
2474.09 lb.
$5539.85
349.24
Econ.
Yield ( 25-48)
-01311.64
633.53
Value
+18.8%
+18.8%
1945.17 lb.
-21.4%
$5835.51 Value +5.1%
+18.8%
414.87
.75/pound
3.00/pound
3.00/pound
.,
..
6
5
FO.I=.14
4
'"
'"
>- 3
~
~
2
oi
o
r
I
1
I
I
I
I
I
I
.1
.2
.3
.4
.5
.6
.7
.8
.9
F (monthly)
Fig.
1.
Ricker yield/recruit all cohort.
1.0
-
17 -
Fig.2
.15
.14
.13
./2
.11
Monthly F
.10
VS
.09
Terminal
Spawning Biomass
-;, .08
-.,;:
-.c
0
.07
<=
~
~
.06
.05
.04
.03
.02
.01
0
0
200
400
600
800
Terminal
Spawning
Biomass
1000
1200
Prawn Ricker Yield Per Recru it
Yield of 3t Cohart
Fmax.066
700
"T1
<0
().I
VS
Different F (fishing mortalities)
600
Fmax.051
_
F 0.1' .041
500
~
o
.s;;;
o
U
_
-
400
r<l
o
~
~
'<>
300
QJ
>200 -j
100 -j I
o1
o
/I
A
Graph of fishing mortalities with time at first
capture 13 months.
8
Graph of fishing mortalities
capture 25 months.
with lime at
first
r
I
I
I
I
I
I
I
I
i
.02
.04
.06
.08
.10
.12
.14
.16
.18
.20
F (monthly)
.,"T1
3500
•
3000
•
•
• ••
F=O.OOO
••• ••• • ••
••
•
•
2500 -I
-l>
•
•
•
<II
<II
o
E
2 2000
lD
1500
•
•
1000
o -I
12
•
•
I
,
14
16
•
•
•
•
•
•
Prawn Residual Biomass
VS
N
•
Age For F (Fishing Mortalities)
•
•
r
I
I
I
I
1
I
,
1
I
,
I
I
I
•
I
18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48
Age (months)
-
23 -
,,
Fig. 5
<Xl
q
,,,
I
I
I'--
q
/
/
I
I
I
,,I
<Xl <Xl
V V
I
I
III
q
I
I()
I
'"
(\J
I
I
I
I
I
I
I
I
CD <l:
I()
I()
I
I()
q
I
I
I
I
I
I
I
V
q
I
I
\
\ I
,
,
,
I
,
,
,
CD
I()
/
/
/
,,
I
/
/
;.-
/
/
~
l<.
'"q
,1\
,
,,
(\J
q
~
I
/
~
"",,
<l:'
I()
/
"
0
""
"
"" ,
/
0
0
III
I()
c::
E
I
/
/
-
.s::
0
/
/
-'"
V
anlo/\ VS
ssowoi8 fiUiUMOdS 8S
'"
(\J
0
- 25 -
SEA UHCH INS:
SUITABILITY UF THE PHESENT MINIMUM SIZE LIMIT
by
Paul A. Breen
Department of Fisheries and UCeans
Fisheries ~esearch tlranch
Pacific ~;olog;ca' Station
Nanaimo. t$.C.
V9H 5K6
ThiS report is in response to a management biologists request for
advice concerning the minimum
size limit in the roe fishery for red sea
urchins (Strongylocentrotus franciscanus), based on present knowledge of sea
urchin biology. The present size limit is 100 O1n in test diameter. The
industry has complained that sea urchins larger than about 125 rrm have poorer
quality gonads (roe) than smaller individuals; and they argue that the size
limit should be reduced to the minimum size which can be processed (about
75 mm).
A.
RATIUNALE BEHINU THE PHESENT LIMIT
When the present size limit of IOU mm was
was in charge of sea urchin research.
received the following response:
imposed~ Ur. F. K. ~ernard
I asked him about the rationale, and
"A size was set because Field Services ~ranch felt some limit was
necessary. We believed a size limit was not necessary as the fiShery
economics would look after this. The 4" (lOU ITJO) test-diameter was
reasonaole, as it did not in fact hinder the fishery and allowed probably 3
spawning years prior to harvest.
II
B.
POSSIBLE FUNCTIONS OF A MINIMUM SIZE LIMIT
limit.
There are several possible purposes for enacting a minimum size
These are:
-
26 -
1) To prevent individuals being harvested at a small average size, when a
greater yield per recruit could be taken by allowing the average size at
harvest to increase.
This consideration is not independent of the level of fishing
effort.
If effort is very low, then average size at harvest will be close to
the average size of available individuals in the virgin population. At very
high levels of effort, average size at harvest will be close to the minimum
size available. In situations where yield is being maximized. the average
size at harvest should be close to 'critical size ' of a cohort, which is the
point where growth balances natural mortality. To do this, the minimum size
should be smaller when effort is low, and larger when effort is higher.
It isn't possible to find the best minimum size without knowing
something about effort. However, the minimum size doesn't matter ruch if
effort is low. If effort is high, then to maximize yield per recruit minimum
size should approach critical size.
2) The minimllJl size can be used to protect part of a population as a
breeding reserve. If fishing effort is very high. the minimum size can be
made large enough so that significant reproduction occurs before
individuals are available to harvest. The minimum size in such a case is
designed to prevent 'recruitment over-fishing ' • For many fisheries, it has
been suggested that a suitable minimum size could function to manage the
fishery by itself, in the way just described. At high levels of effort,
however. reproductive effort can be reduced to a point where recruitment
'fails' (falls below replacement levels). and the population declines.
3) In red sea urchi ns, a speci a1 argument for a si ze 1imit mi ght appear. A
high percentage of juveni les in their first year of 1ife are found
underneath the 'spine canopy' of adults. This appears to result from
active behaviour in both the adults and juveniles. Thus it might be
necessary to ensure that enough adults remain to protect the settlement of
juveniles. This. and the market preference, is the basis for the two-part
size limit used to manage the roe fishery in Washington State. The
Washin9ton State limits are 3.75 and 5.0 inches (95.3 and 127.0 1MI) for
outside waters. and 4.5 and 5.5 inches (114.3 and 139.7 rrm) for essentially
inside waters.
In a related way, a two-part limit might also function to spread out
the effort. When most of the adults are removed from a local area, red sea
urchins re-group in a small part of their former local range. In this
situation. recovery is very slow, as juveniles are found only in the habitat
occupied by adults (Breen, Adkins and Miller 197B).
As with the other two functions of a minimt.m size limit, the effect
of a two-part limit is dependent on fishing effort. At high levels of fishing
mortality, few individuals would survive the period of vulnerability to the
fishery to reach the upper size limit. As protected large adults died Qut.
the upper size limit would protect fewer individuals.
- 27 -
~ASEU
C.
CONSIUERATIONS
UN AVAILABLE UATA
1.
Are smaller sea urchins more suitable for the roe industry?
The scientific inforrnation on this point are scarce.
~il1er
tiernard
&
(1973a) give a relation (their Figure 10. reproduced here as Figure 1)
showing that gonad weight increases with test diameter at a decreasing rate.
Unfortunately. they do not plot the actual data; and among their figures
relating test diameter, body weight and gonad weight contain some
inconsistency. Fiyure 2 shows one of their data sets selected at random and
plotted (Bernard & Miller l~73b). There is no evidence in this figure of a
decreasing rate of gonad weight increase.
Kramer & Nordin (1975) show monthly
plots of gonad weight as a function of test diameter: one of these is shown
here as Figure 3. The data would be described oetter by a power function than
by the straight linear relation used oy these authors. The data clearly
support a continuing upward curve with none of the S-shape imagined by Mernard
& Mi ller.
These data show that gonad weight is continuously. greater in larger
sea urchins. Kramer (" Nordin (1975) examined gonad quality in their study;
but they do not re 1ate Qua 1ity to size. No other authors have exami ned gonad
quality in the local species. Thus there is no information on the relative
quality of gonads from large and small individuals, except for the preference
of the processors.
2. What is critical size?
To estimate the critical size, one compares growth and mortality
rates. Moth might vary with size; but mortality is usually so difficult to
estimate that it is considered to be constant over a wide range of sizes.
a.
Growth
~ernard & Miller (lg73a) publiShed a,.suggested growth rate based on
size frequency shifts. The method by which they elucidated these Shifts is
not given. Figure 4 shows d Ford-walford plot based on the positions of
clearly-defined year classes within all those sea urchin populations measured
by Breen (unpub. data) from 1~79 to the present. From this relation, a growth
curve was constructed. This curve and the curve of ~ernard l!Il Miller are seen
in Figure 5.
The relation between gonad weight and test diameter was determined
from the data set for Llecember 1974 published by Kramer & Nordin (1975) (these
are the same data already seen as Figure 3). This relation was determined to
be:
1n gonad wt(g) = -7.466 + 2.519 In test diameter (1IYIl)
The growth curve and gonad-test diameter relations were combined to
produce the age-gonad weight relation seen in Figure 6, and from this the
instantaneous rate rate of gonad growth was calculated:
•
- 28 -
b.
Mortal ity
Mortality rate was examined with the nethod of iireen 6: Fournier
t l!:ltl3). This method uses known growth parameters and the observed length
frequencies to estimate total lTDrtality. For the rrethod to work well. annual
recruitment to the population should be reasonaDly constant. Repeated
observations at several sites. and the
a~pearance
of size frequencies observea
at mal"\Y sites l for examples see Breen lI. Adkins l!:lbl). inoicate that in many
locations recru1tment is 1nstead quite erratic.
Accordingly. 7 sites were
chosen where gaps in recruitment were not seen, and where extensive
measurements from quadrats had been taken.
TaDle 1 shows the instantaneous mortality rates estimated from these
sites. Estimated total IOOrtality was negative at four of the 7 sites, and
ranged from 0.016 to O.2t: at the remaining three sites. It is not possiole to
have a negat i ve IOOrta1i ty rate. The exp 1anat ions mi ght be one of the
following. or a combination of them:
oortality rate is not constant over the range of sizes analysed; it is
instead hill in small inoiviauals and lQri in larger inoividuals;
- there has been a consistent decrease in recruitment;
- growth parameters have been esti mated wi th 1arge bi ases;
- the data were collected wi th a samp1i ng bi as.
For several reasons, the fi rst of these poss i ble exp 1anat ions seems
most likely. Sea urchins are least vulneraole wring their first year of
life. when they are protected by the spine canopy of adults; then they oecome
highly vulnerable to predators as they grow. finally they become less
vulnerable as they reach a refuge in size. Total mortality rate of adults
IllJst be low for this explanation to work. A value of of u.1-u.£ could be
accepted. as the table suggests. This would correspond with annual survival
rates of l:S2-n'1.. Such an estimate would imply a critical size of at least lJU
rllII. Critical size might be even larger if mortality is, lower.
3. When do sea urchins first reproduce?
Bernard & Miller (1973a) suggest first reproduction at 50 11111.
4. What would be the immediate impact of changing the size limit?
Table 2 gives the length frequency of sea urchins measured at 22
sites in Barkley Sound. Clayoquot Sound and various parts of the north coast
in recent work.. The collective frequency is shown in Figure 7. The meoian
size is just below 100 nm. Between 100 and l~!:l nrn lies 30'1. of the total
population. Only Ib1. are larger than 1~5 mm. the size whicn is reported to be
rejected by the processors. If the size limit were reduced oy ~l5 nrn) 1" to
(75 rrvn) 3". an additional 23\ of tne population would oecome vulnerable to
fishing.
- 29 -
!>. What are the sizes of aaults which are 'parental '?
Figures b ana 9 shOtI' the sizes of 'parental' adults (those with
Juveniles
<~u
mn diameter under their spine canopy) ana non-' parental ' adults
measured at Kunga Islano in April lYb2.
'Parental adults range from aODut y~
nm upward. Although their mean size is larger than non-'parentals·. they
represent a good cross-section of the adult slzes available. Results from
Barkley Sound are similar.
U.
KECU"MENUA',
1UN~
L The two-part size limit
The advantages of a two-part size limit are that it could allow
smaller sizes to be taken than at present. that it would protect 'parental'
size adults. ana that it would spread the effort out over a ldrger area.
There are two disadvantages to using a two-part size limit as the
main conservation tooL First. at hi£l1 levels of fishing effort. few
individuals would recruit to the protected group of large individuals. whiCh
would eventually die out. Thus, the two-part size limit proviaes little real
protection at high levels of effort. Second. gonad quality is dependent as
tood supply lMottel BOb). and there may be strong competition for food in sea
urchin populations (Breen unpub. data). Tne industry claims that reducing
stoCk size, and especially removing the larger individuals, results in
increased gonad quality in the target sizes. A two-part size limit would
largely prevent this effect.
For these reasons. it is recolTlTlended that a two-part size limit not
be emp 1oyed.
~.
The present minimum size limit
It is not clear what function the present size limit performs. At
high levels of effort. the size limit will not maximize yield per recruit.
wiTl allow most of the breeding ~otentlal to be removed. and wl1l not protect
'parental' adults. At the same time. if the anecdotal information concerning
market quality is correct. ~he present limit prevents the fishery trom using
the best part of the stocks.
It seems unlikely that the red sea urchin fiShery snould De managed
by a size limit alone. ~ize limit capaDle of protecting the breeding stock
WOUld probaDly be larger than the inoustry's upper limit for market quality.
A better ITEthod of n\3naging would De by controlling effort or catch in such a
way as to protect local stocks from over harvesting.
- 30 -
REFERENCES
Bernard. F. R' t and O. C. Miller. 1973a. Preliminary investigation on the
red sea urchin resources of British Colunt; a (Strongylocentrotus
franciscanus
(~gassi)).
Fish. Res. Bd. Tech. Rept. 400:
Bernard. F. R. and D. C. Miller.
1973b.
37 pp.
Morphometric data for a preliminary
investigation on the red sea urchin resources of British Columbia
(StrOng~lOcentrotus franciscanu5 Ag.).
Flsh. Res. Bd. Can. MS Rept.
1256:
7 pp.
Breen, P. A., and B. E. Adki os. 1981 . Observ at i cns of abalone populations
on the north coast of British Columbia, July 1980. Can. MS Rep. Fish.
Aquat. Sci. 1633: 55 pp.
Breen. P. A., B. E. Adkins, and D. C. Miller.
1978.
Recovery rate in three
Fish. Mar. Servo MS
exploited sea urchin populations from 1972 to 1977.
Rep. 1446:
27 pp.
Breen, P. A., and D. A. Fournier.
abalone with growth' analysis.
1983.
Estimation of rrortality rate in
Trans. Am. Fish Soc. 112:
403-411.
Kramer, D. E., and D. M. A. Norden. 1975. Physical data fran a study of
size, weight and gonad quality for the red sea urchin (Strongylocentrotus
franciscanus) (Agassiz)) over a one-year period. Fish. Res. Bd. Can. MS
Report 1372:
91 pp.
Mottet, M. G. 1976. The fishery biology of sea urchins in the family
Strongylocentrotidae. Wash. Dept. Fish. Tech. Rep. 20: 66 pp.
-
Table 1.
31 -
Mortality rate estimated from seven
sea urchin populations.
Place
Total mortality
rate (Z)
Lyell Island
-0.039
Hoskins lsI et
0.016
Pelican Point
0.219
Section Cove
0.128
Uhi at Island lY79
-0.154
Uhi at Island 1982
-0.061
Taylor Islet
-U.089
-
32 -
Table 2. Size frequency of all sea urchins observed at 22 sHes, percent
frequency and cumulative percent frequency.
Size
(11Ill )
Number
Percent
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
52
54
56
58
60
62
64
66
68
70
72
74
76
78
80
82
84
86
88
90
92
0.0
0.0
0.0
1.0
17.0
15.0
23.4
23.0
22.4
57.7
55.4
62.7
56.1
61.3
74.3
65.3
61.4
63.1
53.1
36.4
41.7
51.0
37.7
36.0
36.8
43.7
34.7
26.7
32.0
26.4
25.7
31.0
51.0
43.0
38.7
59.0
55.0
77 .0
63.0
103.0
71.0
111.0
114.0
107.0
92.0
114.0
106.0
O.ou
0.00
O.UO
0.02
0.33
0.2Y
0.45
0.44
0.43
1.11
1.07
1.21
1.08
1.18
1.43
1.26
1.19
1.22
1.02
0.70
0.80
0.98
0.73
0.69
0.71
0.84
0.67
0.52
0.62
0.51
0.50
0.60
0.Y8
0.83
0.75
1.14
1.06
1.49
1.22
1.99
1.37
2.14
2.20
2.07
1.78
2.20
2.05
Cumulative
percent
0.00
O.OU
0.00
U.U2
0.35
0.64
1.09
1.53
1.96
3.08
4.15
5.36
6.44
7.62
9.06
10.32
11.50
12.72
13.75
14.45
15.25
16.24
16.97
17.66
18.37
19.22
19.89
20.4U
21.02
21.53
22.02
22.62
23.61
24.44
25.18
26.32
27.38
28.87
30.09
32.07
33.45
35.59
37.79
3Y.85
41.63
43.83
45.88
,
- 33 -
Table 2 (cont'd)
Size
(11111)
Number
94
96
98
lOU
102
104
106
lU8
110
112
114
116
118
12U
97.0
96.0
87.0
B4.0
113.0
121.0
lU1.0
Y9.U
123.U
135.U
135.U
117.0
136.U
137.u
Percent
Cumulative
percent
1.87
1.B5
1.68
1.62
2.1B
2.34
1.Y5
1.Yl
2.37
2.61
2.61
2.26
2.63
2.b4
47.75
49.6U
51.2B
52.YU
55.UB
57.42
5Y.37
61.2B
63.65
66.26
6B.B7
71.12
73.75
76.39
-
160
35 -
TOFINO
FEB.'73
140
E
co
120
lI
<!)
w
;c
0
<I
Z
0
100
BO
<!)
60
40
80
100
TEST
120
140
160
OIAM, (mm)
Fig. 1. Gonad weight-test diameter relationship for red
urchins from west coast of Vancouver Island. from Bernard
and Miller (1973a),
•
-
37 -
180
00
o
o
160
o
140
o
0
0
(f)
data from Bernard &. Miller 1973
0 0
0
BARKLEY SOUND - TOFINO
0
October 6. 1972
0
00
0
120
..
~
100
~
•
Eo<
t;:
~
00 dIDO
COo
80
CD~~
~
0
0
60
§
8°0~0
oEb~
0
0
40
20
o
00
(§>O
0
00 0
o ..1..----,--_ _--,80
TEST
Fig. 2.
100
,--------,----,--120
DIAMETER
140
160
(mm)
Gonad weights vs test diameter from Bernard and Miller (1973b).
(sic)
-
39 -
2110
•
L. DECEMBER
•
•
• •
•••
200
~
•••• •
150
•• •
a-
• ••
••
I,
•...
50
75
100
•• •
•
125
TEST DIAMETER
Fig. 3.
150
nun
Gonad weight vs test diameter from Kramer and Nordin (1975) . .
175
- 41 -
1~0
o
100
It.! = 27.5+0.881t
o
~O
7~
100
LENGTH (mm)
Fig. 4. Ford-Walford plot based on mean lengths of distinct size classes
in all sea urchin samples 1979-1982.
1~0
- 43 -
Breen (in prep.)
1r>O
Bernard
&;
Miller
(1973 a)
O+---.--.----.--.-----r-r----r-r----r---,
o
1
23456789
10
AGE IN YEARS
SEA URCHIN GRd\VTH RATE
Fig. 5. A suggested growth curve based on Fig. 4. compared with the
curve of Bernard and Miller (1973a).
-
45 -
300
~
'"
Gonad
weight
~
Eo< 200
0.110
f"I
Eo<
0==
<II
~
f"I
II:
~
~ 100
0.25 Eo<
==
~
~
0
II:
0
0
0
0
0
110
TEST
100
DIAMETER
150
(mm)
200
Fig. 6. Growth and growth rate of gonads, based on the growth curve
in Fig. 5 and data from Kramer and Norden (1975).
~
47 -
COLLECTIVE SIZE FREO (WHOL E FILE) 22NOV82
517
:II
N.
9.0
:II
MEAN X.
14
>U
z. 12
W
=:J
0
10
W
0:::
LL
B
6
4
20
0
0
30
60
90
120
150
TEST DIAMETER MM
Fig. 7. Size frequency of all sea urchins in 22 population samples,
1979-1982.
- 49 -
KUNGA IS.
39
.. N.
82-19
11.5
PARENTAL ADULTS 82APR10
.. MEAN )(.
>-
u
z
w
:::>
o
W
er:
2
LL
o +nTTT'I'TT1rT'M~,I"'I"T'l""n-n,.,.,.."TTT'Mi',........'I'TT1rTT"1...-H-rH-rrHH-H+H--H+II+H+l++H-I-h-r.....,,..++-.,....,........
, ......
o
30
60
90
120
150
Fig. 8. The size frequency of parental adult sea urchins at Kunga
Island, April 1982.
-
KUNGA IS .
124
>--
u
.., tL
82-19
IDA
51 -
LONE ADULTS
82APR10
.., MEAN X.
IS
z
w
::)
o
w
a:::
6
l.L
4
TEST DIAMETER MM
Fig. 9. The size frequency of non-parental adult sea urchins at
Kunga Island, April 1982.
- 53 -
RECOMMENDATIONS FOR THE 1983 ABALONE SEASON
by
Paul A. Breen
Department of Fisheries and Oceans
Fisheries Research Branch
Pacific Biological Station
Nanaimo, B.C. V9R 5K6
A.
CONCERNS ABOUT THE FISHERY
For at least two years, I have made the following comments to
managers and the industry:
1) We cannot realistically measure abalone stock size with present and
reasonable future resources.
2) Without a very significant increase in resources, we have learned all that
we reasonably can about growth, mortality and recruitment rates.
3) The method of estimating sustainable yield (Breen 1980) contains some
assumptions that further work (Breen and Adkins 1982) has shown to be
faulty. These include the assumptions of constant recruitment and no
sublegal mortality. The failure of these assumptions means that yield
cannot be as high as the estimate of 115 t initially made in 1980.
4) Some areas, which were included in the total area for which the quota was
calculated, are no longer actually available to the fishery. This means
that the remaining area is perhaps being harvested at a higher rate than
the estimated sustainable rate. The 1982 quota was 90.7 t.
5) Stocks are at a low 1evel of abundance that with the natural
around mean density (Breen 1980), it is difficult to measure
changes in abundance. If the present quota management comes
to producing an equil ibrium fishery, it will not be possible
small decreases or increases in density.
vari ance
further
at all close
to measure any
Based on these points, in 1981 it was recommended that the quota be
reduced from 90.7 t to 57 t. After some discussion, management biologists
decided to let the 1982 quota stand at 90.7 t and to watch the fishery
carefully.
- 54 -
While there is no hard evidence that abalone stocks are continuing
to decline (which at this point might be ipso facto evidence of over-fishing),
there are several indications that this is the case. These are:
1) Both the relative catch and catch per unit 'effort (catch/diver day)
continue a long decline in the Charlottes and in the north coast as a
whole. Area b holds its own. The south coast shows an increase in effort.
catch. and catch/effort. The increased catch/effort probably does not
reflect an increased stock size. Instead. it may reflect the deflection of
boats to the south coast. which has not been fished as hard as the north
coast.
2)
Fishery Officers report boats having difficulties finding their quotas in
areas previously having good stocks; this is particularly true in the Queen
Charlotte Islands.
3) Poaching. which was unimportant previously. h~s become a problem in
the Victoria area, as shown by a number of arrests and convictions. The
extent of poaching is unknown in the north coast. Poaching removes stock
that should be included in the quota.
B.
RECO~IMENOATIONS
If stocks really are declining, then this small fishery is in
trouble until a few good year-classes rebuild the stocks. The following
recommendations are made:
l} that a Joint FSB-FRB survey De made in lYt>J to measure density where it was
measured during the period 197t>-19tiO. This survey should involve the
industry; both so that the work is crediole to them, and so that they have
a chance to di rect the surveyors to any good beds they know.
Z) For the reasons outlined above, the quota should be reduced from 9U.7 t.
3) It is recommended that unused parts of the quota at the end of a year not
be carried over into the next year.
4) Since stocks were estimated to have declined by 60-75% (Breen 19t>U) as
early as late 197~. they may now be at a small part of their virgin level.
Although the relation between abalone stock and recruitment is unknown, the
con~ervative cdurse would be to .protect as much breeding potential as
possible. Since the breeding stock includes stunted sub-legal abalone, it
is recommended that requests for permits to transplant surf abalone on a
commercial scale be restricted to limited experimental studies.
- 55 -
REFERENCES
Breen, P. A. 1980. Measuring fishing intensity and annual production in
the abalone fishery of British Columbia. Can. Tech. Rept. Fish. Aquat.
Sci. 947: 49 pp.
Breen, P. A. and B. E. Adkins. 1982. Observations of abalone populations on
the north coast of British Columbia, July 1980. Can. MS Rep. Fish.
Aquat. Sci. 1633: 55 pp~
-
57 -
OBSERVATIONS OF THE B.C. SEA OTTER TkANSPLANT
by
Paul A. Breen
Department of Fisheries anp Oceans
Fisheries Research Branch
Pacific Biological Station·
Nanaimo, B.C. V9R 5K6
This report describes observations made in the area of the British
Columbia sea otter transplant in the Bunsby Islands, 24-28 August 1982.
A.
BACKGROUND
For most of this century, sea otters (Enhydra lutris) have been
absent from British Columbia, or practically so, after very heavy hunting for
their pelts. The last known native animal was shot near Kyuquot in 1928
(Cowan and Guiget 1965). From 1969 through 1972, 89 animals were transplanted
from Alaska to the 8unsby Islands near Kyuquot. These transplants are
described by 8igg and MacAskie (1978).
In the summers of 1977 and 1978 the transplant colony was counted
from the air by Graeme Ellis of the Pacific Biological Station. His estimates
were 55 individuals in the Bunsby Islands and 15 on the Bajo Reefs off Nootka
Sound. From the air, Farr (pers. comm.) obtained a maximum count of 58 in the
Bunsby Islands in 1980.
Derek Ellis, University of Victoria, and his students made
observations in the summer of 1978, as part of the Cook Bicentennial year.
They described the feeding habits and the area occupied by the population
(Morris et ala 1981). In 1979, underwater communities where sea otters had
fed were examined, and the area that had been foraged by sea otters was
surveyed (Breen et ala 1982). We found that sea otters had eliminated sea
urchins almost completely from their feeding range, that other large prey
organisms were absent, and that these areas were characterized by large, dense
st ands of ke 1p.
Sea otters are of particular interest because they are voracious
eaters of shellfish. In Alaska and California their ability to destroy large
numbers of sea urchins has been well described (Estes and Palmisano 1974). In
turn, this allows kelp to increase, with further effects in increased fish,
- 58 -
marine mammal and bird populations (Simenstad et al. 1978). In California the
sea otter is surrounded by considerable controversy because of its alleged
destruction of abalone resources and other commerci al shellfish such as the
Pismo clam and crabs (Cicin-Sain et al. 1977).
B.
PRESENT STUDY
The work described here was carried o'ut by Anne Stewart of Canadian
Benthic Ltd., Wolfgang Carolsfeld, and me. We spent four days in the Bunsby
Islands in early September 1982, and made 11 dives in the area (Fig~ 1). Our
goals were: (1) to examine changes in plant and animal communities at some
sites we had examined in 1979; and (2) to examine any changes in th~
distribution of sea otters in the area. We had not planned on estimating the
number of sea otters, but because of exceptional sea conditions on the last
day we were able to .do so.
1. Distribution of sea otters.
Figure 2 shows the 1979 feeding range of sea otters, based on
underwater observations of their food items. Figure 1 shows the area in which
we saw sea otters from the surface in 1982. If one accepts these two methods
as being roughly comparable, it appears that sea otters have spread through
the Acous Peninsula to the west, as far as Thomas Island to the east, and
along the chain of isolated rocks the the southeast.
That sea otters have expanded their range was suppported by direct
observation of underwater communities. Several sites which had had abundant
red sea urchins (Strongylocentrotus franciscanus) in 1979 now had many fewer,
or none. These were places where sea otters were observed from the surface.
At one site in the Cuttle Islands, sea urchins were still present but were
absent from the shallow part' of their previous range. They were scarce at the
top part of their vertical distribution, indicating the effect of predation.
Surface observations of kelp cover (Nereocystis luetkaeana) also
supported these results. Where we saw sea otters, kelpbeds were wide; outside
the range of sea otters, kelpbeds were restricted to a narrow fringe near the
shore, or were absent. Although we made no formal measurments, it was obvious
to us that Nereocystis was now far more abundant in the Cuttle Islands and at
Thomas Island than it had been in 1979.
Decreased sea urchin abundance and increased kelp cover appeared to
be limited to the area where we saw sea otters. At Quineex Reef, sea urchins
and kelp were the same in numbers and distribution as they had been in 1979.
Similarly, there was little kelp at the next reef east of Quinneex. The
changes we observed were,we think, caused by expansion of the sea otters'
range.
2. Changes in subtidal communities.
The changes we saw in sea urchin and kelp distributions between 1979
and 1982, at several sites to which sea otters moved during that period, have
-
59'-
just been discussed. We also re-examined two sites which had been within the
sea otter feeding range in 1~79, to look for changes in plant community
structure over that period. One site supported a thick Nereocystis canopy,
and a rich understory of mixed Lami nari a setche 11 ii, Pterygophora Cal Horni ca
and Eisenia arborea. The other slte had a thlck canopy of Macrocystls
inte~rifolia and Nereocystis, with a dense understory of Pterygophora.
None
of t ese observatlons were quantitative (nor could they be ln the tlme we
had). In any case, there appeared to have been no major changes in existing
seaweed communities between 1979 and 1982. This is contrary to expectations
based on the literature (e.g. Duggins 1980), which were that the annual
Nereocystis would have been out-competed by the stiff-stiped perenniel kelps
below.
It was not possible to survey food resources of otters within the
old feeding range, which still supports considerable feeding. As in 1979,
there were no apparent food species in the area covered by diving. The
intertidal zone, which may contain sea mussels and gooseneck barnacles, could
not be exami ned because of the heavy surge present (even though the swell was
relatively low). The sea otters may be feeding on the sand and shell bottom
below the feet of the rocky islets, but these areas were too deep for us to
explore.
2. Numbers of sea otters.
During causal observations from a rubber boat in the late afternoon
of 27 August, .we counted at 15 sea otters in the Cuttle Islands. On the next
morning, we saw the following number of sea otters from the boat in the area
from Clara Islet east:
Clara complex:
50 (at 1east 6 pups inc 1uded)
Farout Rocks:
(possibly several more)
5 (possibly 3 more)
West Rock:
1
Stink Rock:
13 (including at least 5 pups)
Double Rock:
0
Fl at Top Rock:
0
Six Foot Rock:
0
These counts were made on a very clear day in a flat calm with
little swell. In these conditions, it was possible to spot otters from a long
way off, and we checked all the major outlying rocks to the east of the Clara
Islet complex. The 50 sea otters we saw in Clara were in a compact group when
we first approached. The number of this large group was determined from
photographs; and also by landing an observer on a small rock, then moving the
boat so that the group swam past him.
-
60 -
It is not possible to know whether the counts on August 28 included
otters that were counted the previous afternoon; but clearly the minimum
number of otters present was the least number counted on August 28: 69
animals. If the Cuttle Islands group were not counted again the next day,
there may be 90 sea otters in this area.
C.
DISCUSSION
The persistence of this small colony for at least 10 years, and its
expansion from 55 to at least 69 over the last 3 years, are grounds for
optimism that the transplant will be a success. At the same time, any
population this small is obviously extremely vulnerable. The colony is
especially vulnerable because of the small qreq it occupies, and because of
the degree to which it is concentrated socially - we saw more than half the
total popul ation in -one tight group; and nearly all the mothers and pups in
two groups. Dangers invited by these facts include damage from an oil spill
or chemical spill (sea otters would not survive being oiled), harassment by
people, predation by whales.
The existing Ecological Reserve merits recognition by the Department
of Fisheries and Oceans for the following reasons:
1) Most of the area now occupied by the colony is within a large marine
Ecological Reserve which was established in 1981 to protect this sea otter
colony. Reserves ~e not automatically recognized by the Department, and
some scouting for commercial geoduc (Panope abrupta) beds (possibly some
fishing as well) has taken place. Commerclal geoduc fishing could
interfere with sea otters in several ways. First, sea otters are known to
take 'white clams' from the area (Morris et al. 1981). It is unlikely (but
not totally impossible) that these are geoducs. The resource of these
clams could be damaged incidentally by geoduc harvesting. Second, the
physical presence of commercial fishing boats in the area (especially in
the Clara group, where most of the mothers and pups were seen) might cause
disturbance damage. Third, sea otters may be using the siphons of geoducs
as prey.
A more immediate conflict exists over red sea urchins. There is
continuing interest in a commercial red sea urchin fishery, and the
Kyuquot/Fair Harbour area has extensive stocks accessible to a road-head.
There are still substantial numbers of sea urchins within the ecological
reserve.
This population, resulting from a transplant carried out by the
Department with other agencies, appears to be increasing and expanding. The
evidence from elsewhere (particularly California) is clear that serious
conflicts may develop as the population spreads: some prime areas for conflict
are crabs in the Tofino area, sea urChins on the whole outer coast of
Vancouver Island, and abalone in the area from Port Renfrew to Victoria.
Against these problems, sea otters provide several potential opportunities:
scientific, economic and esthetic. For a more complete discussion see Farr
and Bunnell (1980) and Cicin-Sain et ale (1977).
- 61 -
One possible approach might be to prevent sea otter expansion to
avoid conflict. This would be a short-term solution only: sea otters have
expanded into southeastern Alaska and will re-colonize B.C. from there by the
end of this century (Bigg, pers. COlTiIl.) It is important to recognize .and
discuss the problems and opportunities now, while the situation is still snlall
and is still calm.
3) The work described above, by three people working out of a small boat for
four days, is the only work that has been done on this population since
1979. Apart from that, no work has been Gone on the numbers or the
distribution of sea otters. Since we know that the colony will cause
interest and perhaps problems if it increases and expands, we should know
how fast (if at all) it is increasing and expanding.
To follow the numbers of individuals present, aerial surveys should
be conaucted at least every 2 years, using the techniques developed in Alaska
and California. To follow the expansion of the colony, 1 suggest aerial
photography of kelpbeds. The l:>ritish Columbia fvlarine Resouces i:$ranch and the
Herring Section of the Fisheries Research l:>ranch have Doth used aerial
photgraphy successfu 11y to ae 1i neate kelp di stri buti ons; fvlRi:5 made overfl i ghts
in the mid-7U's in the Bunbsy Island area. At least the area from Cape cook
to Fair Harbour, and if possible the area from Nootka to Cape Scott, should be
photographed for baseline purposes, and the area occupied by sea otters should
be photographed every alternate year.
REFERENCES
Bigg, M.A., and I.B. MacAskie. 197~. Sea otters re-established in British
Columbia. J. lVlammal. 59(4): 874-87b.
Breen, P.A., LA. Carson, J.B. Foster, and LA. Stewart. 1~8L. Changes in
subtidal community structure associated with the British Colurroia sea
otter transplants. iVlar Ecol. Prog. Ser. 7(1): U-LU.
Cicin-Sain, 1:L, J.E. Noore, and A.J. Wyner. 1977. tVlanagement approaches for
marine fisheries: the case of the California abalone. University of
California ~ea Grant Program, ~ea Grant Publication 54: 1-223.
Cowan, 1. [VlcT. and C. J. Guiget. lS1bt>. The mammals of i:$ritish Columbia.
British Columbia Provo [Vlus. Handbook 11: 414 pp.
Duggins, 0.0. l~~O. Kelp beds and sea otters: an experimental approach.
Ecology b1(3): 447-453
Farr, A. C. [vI. and F. L. Bunnell. l~ti(j. The sea otter in British Columbia
a problem or opportunity. pp. 1l0-12~. In R. Stace-Smith, Lois Johns
and Paul Joslin (eds): Threatened and endangered species and habitats in
British Columbia and the Yukon. B.C. Fish and Wildlife Branch, Victoria,
B.C.
- 62 -
Morris~ R.L., ll.V. Ellis, and B.P. Emerson.
lS/tH. The I3ritish Columbia
transplant of sea otters (Enhydra lutris). 8io1. Cons LlJ: ~YI-L%.
Simenstad, C.A.,J.A. Estes, and K.W. Kenyon. 1~7ts. Aleuts, sea otters and
alternate stable-state communities. Science LUlJ: 4lJ3-411.
Stewart, E.A., J.B. Foster, T.A~ Carson, and P.A. Breen. 19~2. Observations
of kelp, sea urchins and other invertebrates made in the area of the
I3ritish Columbia sea otter transplant. Can. IVIS Rep. Fish. Aquat. Sci.
16b5: 28 pp.
rt
v
I
I
r
./
\
/
f'\\
~
'"'j
'? .J
\".",:.~
1,., .....
r·.. (
\
/1
'
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)
c-,
'-
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'"
\1\~V,J
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\\\
\.""}
~l.s,
,)
,-
'\,.,
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' .. /
'I
.I
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'.. . '*' '-
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(:.... ~
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<...... .-..
\
)
,~.)_.
D
o t'
':~:;) \..~:~!
~."
(" ......../'
L.'
G···
1'-.../
"
(:-'fi(,.. \ f ' " l )
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Fig. 1. The sites of 1982 dives.
from the surface in August 1982.
;;, ..
/
l-. -.. --.."./'
')
o
--.
l.~, '~"\ 'fl ....
The line encloses the area in which sea otters were seen
'1l.. ~:·\
.rt
v
I
\
)1"' ....-
5/
r.
/,/
'/(,f.;,,:...
(..I
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,~
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;"J
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\, \1-S '"
'......
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'-,r
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',. -."
I
.... ,
,_, /.J
.:..0
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-'I
,
• 10
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",.
::-:)
( ',//-'
:':/
'.
/'"1.J
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j
\
'-"~~~"c j
f~;'~
\....;
,
~
.,
49'
:1
t.'
::::;~~( r..~i{),
r
c.-'.........
./
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SOl)
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Fig. 2. Area of British Columbia sea otter transplant. Sea otter feeding range determined
underwater in September 1979 delineated by solid straight lines.
'¥J "1
'"1 iL.. ~:-
- 67 -
SCALLOP SIZE LIMITS
by
Neil Bourne
Department of Fisheries and Oceans
Fisheries Research Branch
Pacific Biological Station
Nanaimo, B.C. V9R5K6
Scallop resources along the British Columbia coast are erratic in
distribution and limited in abundance and fisheries that develop for stocks
will be minor but could have some importance locally to a few fishermen. The
fisheries could be quite sporadic; populations could be exploited for a month
or two or perhaps a year and then not be touched for a peri od of years; thi s
could be dependent on popul ation size but al so on markets and socio-economic
conditions. With such minor fisheries it is questionable how much time,
manpower, and funds Fisheries will be able to devote to enforcing any proposed
regulations. The following are suggestions that can be considered in
formulation of any regulations for management of scallop fisheries that might
develop.
Four species of scallops are either large enough or occur in
sufficient abundance to offer some potential in either the commercial or
recreational fisheries:- weathervane, Patinopecten caurinus; rock, Chlamys
gigantea; pink, l. rubida; and spiny, c. hastata.
Rock scallops attain a 1arge size and have a scattered di stribut ion
although there are few if any dense centers of concentration. They are found
firmly cemented to rocks and do not lend themselves to a dragging type
fishery. At present they may be harvested only in the recreational fishery
and a bag limit of six per person per day south of Cape Caution and 12 per
person per day north of it is in place. The present regulations are felt to
be adequate. A size restriction is probably not warranted because people
aren1t interested in harvesting this species until it is a reasonable size by
which time they have been sexually mature and capable of spawning· for several
years.
Weathervane scallops have an erratic distribution but there are two
small centers of population; one in McIntyre Bay and one in the Plumper
Sound - Trincomali Channel area in the Gulf Islands (Bourne 1969). There is
the possibility that local dense beds may be found at some time in the future
off the British Columbia coast because of recruitment of one or two strong
year classes as occurred off Oregon in 1981.
-
68 -
The two small populations in McIntyre Bay and Trincomali Channel
will not support sustained fisheries at even modest levels. A recent estimate
of population density in the Trincomali Channel area was 1 scallop per 65 sq
meters. If a fishery is permitted in 'either location the most practical
management scheme is probably a size limit. Establishment of quotas isn't
warranted since the population is so small and quotas would have to be
mon itored. It wi 11· probab ly be di fficul t to manage the fi shery by a gear
regulation since a variety of home-built gear will be used with a variety of
mesh types although total gear width could be used. If the fishery is managed
by a size regulation it is suggested the minimum size limit be 120 mm shell
height (=4.7 y), distance from the hinge to the ventral margin of the shell.
Our work (.unpubl ished) and that of Haynes and Hitz (1971) indicates
weathervane scallops of this size would be about four years of age, would have
been sexually mature for two years and could have spawned for two years prior
to entering the fishery. While maximum Y/R would be achieved with
exploitation at 135 mm (=6 yr) (Fig. 1), an initial lower size limit should
facilitate establishment of a fishery. If scallops were landed whole there
would be no problem in enforcing a size limit. If they are shucked at sea a
shell height to weight of adductor muscle relationship would have to be
established.
If offshore beds of weathervane scallops, sufficient to support a
commercial fishery, are found off the British Columbia coast it is suggested
the most practical management scheme would be a size regulation. A minimum
size should probably be smaller than inshore because growth of offshore
scallops is considerably slower than those inshore (Haynes and Hitz 1971). It
is suggested it be 100 mm shell height.
Pink and spiny scallops have a scattered distribution but they occUr
in beds of sufficient density to permit small scale fisheries; e.g. off
Victoria. We have little information on the size of these beds. Size
frequency distribution of the population off Victoria indicates recruitment is
reasonably consistent. Growth is slow, maximum size is about 85 mm and they
are 4-5 years at this size. Fisheries for these two species will probably be
minor, they will depend on population size and markets. It is unlikely that
Fisheries could or would survey each bed to establish sustained yields or
quotas. Management by gear is also impractical. The most expedient
management scheme is probably a size li!TIit. It is arbitrarily suggested that
the minimum size be 60 mm shell height for both species. Natural mortality.
rates are poorly documented and so Y/R analyses are felt to be inappropriate
at this time. Initial studies indicate animals of this size would be over two
years and would have been sexually mature and capable of spawning for one
year. Our studies indicate growth after this size slows markedly.
- 69 -
REFERENCES
Bourne, N. 1969. Scallop resources of British Columbia.
Canada Tech. Rep. 104: 60 pp.
Fish. Res. Board
Haynes, Evan B., and Charl es R. Hitz. 1971. Age and growth of the gi ant
Pacific sea scallop, Patinopecten caurinus, from the Strait of Georgia
and outer Washington coast. Fish. Res. Board Can. 28(9): ,1335-1341.
-
70 -
Table 1. Growth and natural mortality
parameters used in the yield per
recruit calculations for inshore
weathervane scallops.
Parameter
M
K
to
L
W
Value
0.1
0.36
0.6
156.8 mm
346 g (whole weight)
-
Yield Contour Diagram
71 -
for Weathervane Scallops in gm.
16
15
14
13
12
II
QJ
E 10
'-
a..
I
9
a::
I-
8
7
160
6
5
4
150
Ilq120
",
'--
140
'--
I~O
Fig. 1. Yield isopleths (gm) per scallop calculated for Gulf Island
scallops as per parameters in Table 1.
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