C S A S S C C S

C S A S S C C S
CSAS
SCCS
Canadian Science Advisory Secretariat
Secrétariat canadien de consultation scientifique
Research Document 2011/114
Document de recherche 2011/114
Central and Arctic Region
Région du Centre et de l’Arctique
Binational Ecological Risk Assessment
of Bigheaded Carps
(Hypophthalmichthys spp.) for the
Great Lakes Basin
Évaluation du risque écologique posé
par les carpes à grosse tête
(Hypophthalmichthys sp.) dans le
bassin des Grands Lacs
Becky Cudmore1, Nicholas E. Mandrak1, John M. Dettmers2, Duane C. Chapman3, and Cynthia S. Kolar4
1
Fisheries and Oceans Canada, Centre of Expertise for Aquatic Risk Assessment
867 Lakeshore Road, Burlington, ON L7R 4A6
2
Great Lakes Fishery Commission
2100 Commonwealth Blvd, Ste 100, Ann Arbor, MI 48105
3
U.S. Geological Survey, Columbia Environmental Research Center
4200 New Haven Road, Columbia, MO 65201
4
U.S. Geological Survey - Ecosystems
12201 Sunrise Valley Drive, MS-301, Reston, VA 20192
This series documents the scientific basis for the
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© Her Majesty the Queen in Right of Canada, 2012
© Sa Majesté la Reine du Chef du Canada, 2012
TABLE OF CONTENTS
ABSTRACT................................................................................................................................... v
RÉSUMÉ...................................................................................................................................... vi
1.0
INTRODUCTION...............................................................................................................1
1.1 THE RISK ASSESSMENT PROCESS ...............................................................................4
2.0 PROBABILITY OF INTRODUCTION.....................................................................................7
2.1 LIKELIHOOD OF ARRIVAL.................................................................................................7
2.1.1 Physical Connections..................................................................................................7
2.1.2 Human-mediated Release .........................................................................................13
2.1.3 Summary of Likelihood of Arrival ...............................................................................19
2.2 LIKELIHOOD OF SURVIVAL ............................................................................................21
2.2.1 Food Resources........................................................................................................21
2.2.2 Thermal Tolerance ....................................................................................................22
2.2.3 Summary of Likelihood of Survival.............................................................................22
2.3 LIKELIHOOD OF ESTABLISHMENT ...............................................................................23
2.3.1 Spawning and Nursery Habitat .................................................................................24
2.3.2 Estimated Spawning Population Needed for Establishment .....................................25
2.3.3 Survival of Early Life Stages .....................................................................................26
2.3.4 Stock Required for Effective Recruitment .................................................................27
2.3.5 Positive Population Growth .......................................................................................29
2.3.6 Summary of Likelihood of Establishment ..................................................................29
2.4 LIKELIHOOD OF SPREAD ..............................................................................................30
2.4.1 Dispersal ...................................................................................................................30
2.4.2 Human-mediated Dispersal.......................................................................................32
2.4.3 Lake Superior............................................................................................................35
2.4.4 Lake Michigan ...........................................................................................................36
2.4.5 Lake Huron................................................................................................................37
2.4.6 Lake Erie ...................................................................................................................38
2.4.7 Lake Ontario..............................................................................................................39
2.4.8 Summary of Likelihood of Spread ..............................................................................40
2.5 SUMMARY OF PROBABILITY OF INTRODUCTION .......................................................40
3.0 MAGNITUDE OF ECOLOGICAL CONSEQUENCES .........................................................41
3.1 LAKE SUPERIOR .............................................................................................................42
3.2 LAKE MICHIGAN ..............................................................................................................42
3.3 LAKE HURON ...................................................................................................................43
3.4 LAKE ERIE (INCLUDING LAKE ST. CLAIR) .....................................................................43
3.5 LAKE ONTARIO................................................................................................................44
3.6 SUMMARY OF MAGNITUDE OF ECOLOGICAL CONSEQUENCES ..............................44
4.0 OVERALL RISK ASSESSMENT ..........................................................................................45
5.0 CONSIDERATIONS..............................................................................................................45
6.0 TARGETTED MANAGEMENT QUESTIONS .......................................................................47
7.0 REFERENCES .....................................................................................................................50
iii
Correct citation for this publication:
Cudmore, B., N.E. Mandrak, J. Dettmers, D.C. Chapman, and C.S. Kolar 2012.
Binational Ecological Risk Assessment of Bigheaded Carps (Hypophthalmichthys spp.)
for the Great Lakes Basin. DFO Can. Sci. Advis. Sec. Res. Doc. 2011/114. vi + 57 p.
ABSTRACT
Bigheaded carps (Bighead and Silver carps) are considered a potential threat to the Great
Lakes basin. A binational ecological risk assessment was conducted to provide scientifically
defensible advice for managers and decision-makers in Canada and the United States. This risk
assessment looked at the likelihood of arrival, survival, establishment, and spread of bigheaded
carps to obtain an overall probability of introduction. Arrival routes assessed were physical
connections and human-mediated releases. The risk assessment ranked physical connections
(specifically the Chicago Area Waterway System) as the most likely route for arrival into the
Great Lakes basin. Results of the risk assessment show that there is enough food and habitat
for bigheaded carp survival in the Great Lakes, especially in Lake Erie and productive
embayments in the other lakes. Analyses of tributaries around the Canadian Great Lakes and
the American waters of Lake Erie indicate that there are many suitable tributaries for bigheaded
carp spawning. Should bigheaded carps establish in the Great Lakes, their spread would not
likely be limited and several ecological consequences can be expected to occur. These
consequences include competition for planktonic food leading to reduced growth rates,
recruitment and abundance of planktivores. Subsequently this would lead to reduced stocks of
piscivores and abundance of fishes with pelagic, early life stages. Overall risk is highest for
lakes Michigan, Huron, and Erie, followed by Lake Ontario then Lake Superior. To avoid the
trajectory of the invasion process and prevent or minimize anticipated consequences, it is
important to continue to focus efforts on reducing the probability of introduction of these species
at either the arrival, survival, establishment, or spread stage (depending on location).
v
RÉSUMÉ
Les carpes à grosse tête (y compris la carpe argentée) sont considérées comme un risque
potentiel pour le bassin des Grands Lacs. Une évaluation binationale des risques écologiques a
été réalisée afin de pouvoir formuler des conseils scientifiques crédibles à l'intention des
gestionnaires et des décideurs du Canada et des États-Unis. Dans le cadre de cette évaluation,
on s'est intéressé à la probabilité de l'arrivée, de la survie, de l'établissement et de la
propagation des carpes à grosse tête afin de parvenir à une probabilité globale d'introduction.
Les voies d'arrivée qui ont été étudiées sont les connexions physiques ainsi que les rejets dont
les humains sont à l'origine. Selon les conclusions de l'évaluation des risques, les connexions
physiques (et en particulier la voie maritime du secteur de Chicago) sont la voie d'arrivée la plus
probable des carpes à grosse tête dans le bassin des Grands Lacs. Les résultats de l'évaluation
montrent aussi qu'il y a assez de nourriture et d'habitats pour que les carpes à grosse tête
survivent dans les Grands Lacs, surtout dans le lac Érié et dans les échancrures productives
des autres lacs. Des analyses des tributaires des Grands Lacs canadiens et des eaux
américaines du lac Érié ont révélé que de nombreux tributaires sont propices à la fraie des
carpes à grosse tête. Si les carpes à grosse tête devaient s'établir dans les Grands Lacs, leur
propagation ne s'y limiterait probablement pas, et plusieurs conséquences écologiques seraient
à escompter. Ces conséquences sont notamment la concurrence des espèces pour l'accès au
plancton, ce qui entraîne la réduction des taux de croissance et du recrutement ainsi qu'une
abondance des planctophages. L'établissement des carpes à grosse tête dans les Grands Lacs
mènerait par la suite à la diminution des stocks de piscivores et à une abondance de poissons
pélagiques et dans leurs premiers stades de vie. Le risque global est le plus élevé pour les lacs
Michigan, Huron et Érié, puis le lac Ontario, et enfin le lac Supérieur. Afin d'éviter la trajectoire
du processus d'invasion et de prévenir ou minimiser les conséquences anticipées, il est
important d'axer les efforts sur la réduction de la probabilité de l'introduction de ces espèces au
stade de l'arrivée, de la survie, de l'établissement ou de la propagation (selon l'endroit).
vi
1.0 INTRODUCTION
The establishment of nonnative aquatic species can have negative, sometimes significant,
consequences to the invaded ecosystem (Moyle and Light 1996, Rahel 2002), leading to
considerable challenges for resource managers. Nonnative species can cause severe reduction
or extirpation of native species (Dextrase and Mandrak 2006, Mandrak and Cudmore 2010),
reduction in the abundance or productivity of sport, commercial, or culturally important species,
and can result in significant habitat alteration (Rahel 2002). Consequently, these invasive,
nonnative species are considered a threat to aquatic biodiversity at the same level as habitat
loss and alteration (Light and Marchetti 2007).
The Great Lakes have not been immune to the arrival of aquatic invasive species. At least 69
nonnative fish species have been introduced to the Great Lakes, half of which are considered
established (Mandrak and Cudmore 2010). The invasion of destructive aquatic invasive species
(AIS) (e.g., Sea Lamprey (Petromyzon marinus)) into the Great Lakes, and the resulting
necessity for intensive management activities and associated costs, has promoted management
strategies that now focus on the prevention of establishment by new aquatic invasive species
(Ricciardi et al. 2011). The mandate of Fisheries and Oceans Canada’s (DFO) Centre of
Expertise for Aquatic Risk Assessment (CEARA) is to identify potential invaders to all parts of
Canada, assess their ecological risk, and provide science advice towards preventing the
introduction of those species considered to be high risk. As noted by Kolar et al. (2007),
Chapman and Hoff (2011), and Cudmore and Mandrak (2011), two species that currently
threaten to invade the Great Lakes are Bighead Carp (Hypophthalmichthys nobilis) and Silver
Carp (H. molitrix), herein referred to as bigheaded carps. The term Asian carps in this document
is used to refer collectively to Grass Carp (Ctenopharyngodon idella), Bighead Carp, Silver
Carp, and Black Carp (Mylopharyngodon piceus).
Bigheaded carps were first imported into the United States in the 1970s for use as water quality
control agents and for foodfish culture. They subsequently escaped intended areas of
introduction into natural waters (Chapman and Hoff 2011). For a detailed history on the use and
introductions of these species in the United States, see Kelly et al. (2011). Previous risk
assessments identified broad, potential risks to Canada and the United States, including the
Great Lakes (Mandrak and Cudmore 2004, Kolar et al. 2007). While these risk assessments
provided insight into the risk faced by broad areas of North America, knowledge gaps were
identified as a result of the lack of information, at the time, on these species in established
populations outside of their native range. As bigheaded carps have moved farther north up the
Mississippi River basin, concern for movement into the Great Lakes has increased (see Figure
1 for current distribution). Now that further research has been conducted on the species in their
introduced range, more available knowledge can be applied to our understanding of the risks
associated with an invasion by these species. The purpose of this risk assessment is to
determine the risk to the Great Lakes and to provide useful, scientifically defensible advice on
subsequent prevention, monitoring, early detection, and management actions that are
underway, or could be taken.
1
a
b
Figure 1. Nonnative occurrences of a) Bighead Carp (Hypophthalmichthys nobilis) and b) Silver Carp (H.
molitrix) in the United States. Dots represent confirmed sightings and collections, not necessarily
established populations. Maps courtesy of the U.S. Geological Survey.
2
The scope of this risk assessment was determined by workshop participants consisting of Great
Lakes researchers, managers, and decision-makers (see Section 1.1). The risk assessment
considers the available information known about bigheaded carps to assess the likelihood of
arrival, survival, establishment, and spread within 20 years, and the magnitude of the ecological
consequences (up to 20 years and up to 50 years) to the connected Great Lakes basin (defined
as the Great Lakes and its tributaries up to the first impassable barrier (Figure 2)). For this
assessment, Lake St. Clair is considered to be part of the Lake Erie basin. We recognize that
Grass Carp and Black Carp, two other Asian carp species, also pose a concern for the Great
Lakes (Nico et al. 2005, Cudmore and Mandrak 2011, Nico and Jelks 2011); however, due to
resource and time limitations, it was determined that the scope of this risk assessment would
focus on the Great Lakes managers’ two highest priority Asian carp species, Bighead and Silver
carps. Largescale Silver Carp (Hypophthalmichthys harmandi), although a bigheaded carp
species, was not assessed due to the low level of risk this species poses to the Great Lakes
(Mandrak and Cudmore 2004, Kolar et al. 2007).
Figure 2. The connected Great Lakes basin, defined as the Great Lakes and its tributaries up to the first
impassable barrier (outlined in red). Modified from Hedges et al. (2011).
This ecological risk assessment focuses only on the ecological consequences; the socioeconomic consequences will be assessed separately using the results of the ecological risk
assessment. It also addresses only the current state, with management measures that were in
place during the scoping of the risk assessment (November 2010). It does not assess
3
effectiveness of measures in place nor the level of risks associated with a variety of potential
mitigating factors that are not currently in place.
Targeted management questions were obtained from Great Lakes managers and decisionmakers at the outset of the risk assessment process. This was done to ensure this risk
assessment provides the most useful advice possible to address the needs of managers and
decision-makers throughout the Great Lakes basin.
1.1 THE RISK ASSESSMENT PROCESS
The format of the binational ecological risk assessment for bigheaded carps in the Great Lakes
basin follows guidance provided in the “National Detailed-Level Risk Assessment Guidelines:
Assessing the Biological Risk of Aquatic Invasive Species in Canada” (Mandrak et al. 2012).
This process serves to summarize the best available information and identify the relative risks
posed to a specified area within a specified timeframe by a nonnative species. Risk
assessments provide a framework for organizing and reviewing relevant information to provide
scientifically defensible advice to managers and decision-makers.
As a first step in conducting an ecological risk assessment, the known biological information of
the species is compiled into a biological synopsis. Kolar et al. (2007) provided biological
information on bigheaded carps, and documented instances where they have impacted aquatic
communities. To update Kolar et al. (2007), which used information published up to 2006, Kipp
et al. (2011) used information published from 2006 to early 2011. Both of these documents
relied heavily on available English literature. Naseka and Bogutskaya (2011) annotated the
available Russian language literature on bigheaded carps, which was also used as a source of
background information on the biology of these species for this risk assessment.
Other documents were developed to support the risk assessment and include ecosystem
modelling (Currie et al. 2011) and a Canadian tributary analyses (Mandrak et al. 2011). Primary
literature and publicly available reports were also used to inform the risk assessment. In some
cases, personal communication, personal observation, and other draft information supplied to
the risk assessment authors were used. This was done to utilize as much up-to-date, if not yet,
published, information as possible to inform the risk assessment. Researchers who provided
draft information or personal communication/observation/data retain the intellectual
property of that work and their information should not subsequently be cited outside of
the risk assessment work presented here. Permission for use was provided for this
process and product only.
Workshops were held in November 2010, May 2011, and June 2011 to develop the scope of the
risk assessment, obtain management questions, and to understand the research occurring on
both sides of the border that could provide input into the risk assessment.
After the risk assessment parameters were scoped, the definitions for risk ratings (Table 1),
certainty (Table 2), and consequences (Table 3), as used in this risk assessment, were
determined by the authors (and agreed upon by peer review experts), following guidance
provided in Mandrak et al. (2012).
4
Table 1. Likelihood as probability categories.
Likelihood
Very Unlikely
Low
Moderate
High
Very Likely
Probability Category
0.00 - 0.05
0.05 - 0.40
0.40 - 0.60
0.60 - 0.95
0.95 - 1.00
Table 2. Relative certainty categories.
% Level
± 10%
± 30%
± 50%
± 70%
± 90%
Certainty Category
Very high certainty (e.g., extensive, peer-reviewed information)
High certainty (e.g., primarily peer reviewed information)
Moderate certainty (e.g., inference from knowledge of the species)
Low certainty (e.g., based on ecological principles, life histories of similar species,
or experiments)
Very low certainty (e.g., little to no information to guide assessment)
Table 3. Description of ecological consequence ratings.
Consequence
Rating
Negligible
Low
Moderate
High
Extreme
Description
Undetectable changes in the structure or function of the ecosystem.
Minimally detectable changes in the structure of the ecosystem, but small
enough that it would not change the functional relationships or survival of
species.
Detectable changes in the structure or function of the ecosystem.
Significant changes to the structure or function of the ecosystem leading to
changes in the abundance of native species and generation of a new food
web.
Restructuring of the ecosystem leading to severe changes in abundance of
ecologically important species (those considered dominant or main drivers in
the ecosystem) and significant modification of the ecosystem.
Although the risk assessment targets the Great Lakes basin as a whole, to accommodate
resource managers who wished to better understand the risk to a particular lake, the risk
assessment does take into account each Great Lake separately. This risk assessment does not
address a finer geographic scale, such as specific impacts within a particular bay or lake subregion, as this is beyond the scope of the current project.
Mandrak et al. (2012) divided the risk assessment process into two steps: 1) estimating the
probability of introduction (using likelihood of arrival, survival, establishment, and spread); and,
2) the determination of the magnitude of the ecological consequences once the species has
been introduced, established, and has spread. The evaluation of the probability of introduction
and the magnitude of the ecological consequences are based on a qualitative scale (see Tables
1 and 3, respectively), and includes a corresponding ranking of certainty (see Table 2). For this
risk assessment (as the basin is interconnected), the overall probability of introduction was
determined by taking the highest ranking between overall arrival and spread, then evaluating
this rank with the ranks of survival and establishment, and using the lowest rank of the three.
This is represented by the following formula:
5
Probability of Introduction = Min [Max (Arrival, Spread), Survival, Establishment]
The probability of introduction and the magnitude of the ecological consequences are combined
into a risk matrix to obtain an overall risk (see Figure 3 for a species-specific example). To
combine certainties between the risk assessment elements, the certainty associated with the
highest rank was used or, if two or more certainties were the same, the certainty associated with
the highest rank was used. Each lake was assessed for two different time periods, within 20
years and within 50 years, to show any increase in consequences over time. Therefore, two
matrices are presented at the end of the risk assessment, one for 20 years and one for 50
years. The ellipse illustrates the amount of certainty associated with the point.
Figure 3. Graphic representation to communicate the overall risk. Matrix combined probability of
introduction and magnitude of consequences for a species-specific risk assessment. From Mandrak et al.
2012.
A draft of this risk assessment was presented to expert peer reviewers who attended a peer
review meeting November 8-10, 2011. Participants of the peer review included the authors of
the risk assessment and bigheaded carp experts. Freshwater invasive fish or invasive modelling
experts also participated. Some participants who had not been strongly engaged in the scoping
of the risk assessment were included to maximize objectivity in the process. The peer review
process followed the guidelines set out by Fisheries and Oceans Canada’s Canadian Science
Advisory Secretariat (CSAS). Documentation of the proceedings (DFO 2012a) of the peer
review meeting that reviewed this risk assessment and a science advisory report (DFO 2012b)
have been completed in support of this risk assessment. The risk assessment contains the body
of information used to develop the overall risk, across all risk assessment elements, by
6
consensus of the peer review participants. It is the definitive science document of this process
and includes science advice. The science advisory report is essentially an executive summary
of the risk assessment coupled with science advice, and may be most appropriate for those who
do not wish to read all the details in the risk assessment. The proceedings document serves as
a record of the discussions and decisions at the peer review meeting. For further information
and details about this peer review, science advisory process, see http://www.dfompo.gc.ca/csas-sccs/index-eng.htm.
The risk assessment rankings are the product of consensus at a peer review meeting (DFO
2012a), not rankings of individuals.
2.0 PROBABILITY OF INTRODUCTION
To determine the probability of bigheaded carp introduction to the Great Lakes basin
information related to the likelihood of arrival (Section 2.1), survival (Section 2.2), establishment
(Section 2.3), and spread (Section 2.4) was used.
2.1 LIKELIHOOD OF ARRIVAL
Arrival of a nonnative species occurs through various forms of pathways and vectors, implying
transit survival. Potential entry routes for bigheaded carps into the Great Lakes were identified
and assessed where information was available. Entry routes discussed in this section are
physical connections (e.g., canals and waterways, and intermittent or occasional connections
around the watershed boundaries) and human-mediated release (e.g., bait use and trade).
Arrival is considered the presence of at least one Bighead Carp or Silver Carp in at least one
part of the Great Lakes basin The likelihood of arrival was evaluated for each Great Lake using
the available information for entry routes to each lake.
2.1.1 Physical Connections
2.1.1.1 Chicago Area Waterway System (CAWS)
The CAWS provides a direct, artificial connection between Lake Michigan and the Mississippi
River basin at Chicago, Illinois and includes natural and artificial waterways, locks and dams
(Figure 4; Moy et al. 2011). Bigheaded carps are well-established in the Illinois River (Irons et
al. 2011). A system of electric barriers (hereafter called the electric dispersal barrier) has been
built in the Chicago Sanitary and Ship Canal (CSSC) near Lemont, IL, the portion of the CAWS
that connects to the Mississippi River basin. The electric dispersal barrier serves to deter
movement of fishes upstream across the barrier. Initially constructed as a demonstration barrier
that became operational on April 18, 2002, the electrical dispersal barrier now includes the
original demonstration barrier (Barrier I) and two more barriers in close proximity (Barrier IIA and
Barrier IIB) with the primary purpose of preventing upstream movement of bigheaded carps
towards the Great Lakes. Currently, Barrier I and Barrier IIB are operating, with Barrier IIA in
stand-by mode. Reversal of flow in the canal is a rare event of short duration and low velocity
compared to the flow in the downstream direction. Fishes are not likely to be swept into, or
through, the electric dispersal barrier during flow reversals (Holliman 2011). Evidence to date
using Common Carp (Cyprinus carpio) and other large-bodied surrogates for bigheaded carps
7
Figure 4. The Chicago Area Waterway (CAWS) system. Map courtesy of U.S. Army Corps of Engineers.
8
indicates that large fishes are deterred from crossing the electric dispersal barrier (Sparks et al.
2011). A radio-tagged Common Carp did pass through Barrier I on April 3, 2003. It was
subsequently tracked approximately 2.5 km upstream of Barrier I, where it did not move again
(Sparks et al. 2011). It is suspected that either the transmitter was expelled or that the fish died.
Subsequent evaluation of fish movement in the vicinity of the electric dispersal barrier during
2011 also indicated that a transmitter from a Common Carp was found about 4 km upstream of
the electric dispersal barrier on August 11, 2011. Since then, this transmitter has not moved (K.
Baerwaldt, USACE, pers. comm.). Although the mechanism by which this transmitter moved
above the electrical dispersal barrier is not known, it is highly unlikely that it was due to natural
movement. The transmitter was regularly tracked by receivers below the electric dispersal
barrier since its implantation into a Common Carp on October 27, 2010. The transmitter was
tracked moving upstream early on July 5 and then moving downstream, where contact was lost
at 7:31 AM. The transmitter was not heard again until August 11, 2011 as described above.
Twelve receivers were between the point of last contact and where the tag was detected, with
no detections on any of those receivers. One possible explanation is that the Common Carp
was caught by an angler who then disposed of the tag several kilometers upstream of the
electric dispersal barrier. Further studies of greater numbers of tagged fishes would provide
stronger information.
Current information indicates the electric dispersal barrier deters small fishes (less than 137
mm). In tests of the effect of operational parameters of the electric field on Bighead Carp (51-76
mm), the optimal settings to immobilize small fishes were 0.91 V/cm, 30 Hz pulse frequency,
and 2.5 ms pulse duration (Holliman 2011). Small Bighead Carp repeatedly challenged a model
barrier, although they recognized the downstream edge of the electric field. They would
continue to challenge the barrier even after recovering from immobilization. Based on the suite
of operational settings explored and behavior of small (51-76 mm) Bighead Carp, Holliman
(2011) recommended that electric dispersal barrier operational parameters be set at these
levels to deter small fishes. Thus, while operating, the electric dispersal barrier effectively deters
large fishes and, based on laboratory experiments, immobilizes small fishes (< 76 mm).
A Bighead Carp was collected approximately 100 m below electric dispersal Barrier IIA (11 km
below Barrier I) in December 2009 (Moy et al. 2011; outside of the connected Great Lakes
basin) as part of a rotenone operation to allow the US Army Corps of Engineers (USACE) to
conduct required maintenance of Barrier IIA. One Bighead Carp was also collected from Lake
Calumet, on the Lake Michigan side of the electric dispersal barrier, in June 2010. Organisms
shed some of their DNA into the environment (termed eDNA). The presence of bigheaded carp
eDNA has been used as an indicator that bigheaded carps are or have been potentially present
(Jerde et al. 2011). Bigheaded carp eDNA was collected in the CAWS upstream of the electric
dispersal barrier (see http://www.lrc.usace.army.mil/AsianCarp/eDNA.htm) during 2009 and
2011. In addition to the collections in the CAWS, in 2011 one sample tested positive for silver
carp within Lake Michigan. This was one of 13 samples taken by Notre Dame researchers in
Calumet Harbor, adjacent to the locks leading to the CAWS. It is important to note that the rate
of false positives of eDNA (detecting bigheaded carp DNA when not present) is at or near zero
(Battelle Memorial Institute 2010, USEPA 2010), but that eDNA can degrade quickly and that
false negatives (no indication of a bigheaded carp when species is present) for this and
traditional capture methods may be high (see Darling and Mahon 2011, Jerde et al. 2011).
However, collection of bigheaded carp eDNA is not incontrovertible evidence of the presence of
a live bigheaded carp, because eDNA can be transported without a live fish. It remains unclear
whether small numbers of bigheaded carps have traversed or bypassed the electric dispersal
barrier, whether these eDNA reports are false positives or from sources other than living fishes,
or whether bigheaded carps have been
9
present in the CAWS for some time or if they have already escaped the CAWS and entered
Lake Michigan. We thus assume for the purposes of this risk assessment that the invasion
process is at “pre-arrival” for Lake Michigan.
The electric dispersal barrier only deters upstream movement through the canal at that location;
it does not prevent downstream movement or movement bypassing the electric dispersal barrier
by other means. Uncertainty exists about whether bigheaded carps may have moved across
Barrier I before Barrier IIA was operational in 2009. It is possible that Bighead and Silver carps
were in the vicinity of Barrier I long before biologists suspected they might be present. During
this period, Barrier I was renovated and power fluctuations may have kept Barrier I from
operating at optimal effectiveness (Moy et al. 2011). Further, Barrier IIA and IIB require regular
maintenance at intervals of approximately one year.
Two known avenues by which bigheaded carps could bypass the electric dispersal barrier
include the Des Plaines River and the Illinois & Michigan Canal (I&M Canal). The Des Plaines
River joins the CSSC immediately below the Lockport Lock and Dam, about 13 km downstream
of the electric dispersal barrier. The river parallels the CSSC for about 24 km upstream, within
about 400 m of one another. During flood conditions, the Des Plaines River can be overtopped
and water from the Des Plaines River will flow over land into the CSSC. Further, DNA sampling
in the Des Plaines River between the Hoffmann Estates Dam and the confluence with the CSSC
has detected bigheaded carp DNA since 2010, suggesting that bigheaded carps could move
from the Des Plaines River into the CSSC during flooding. During 2010, the USACE installed a
combination jersey barrier and mesh fence along the nearly 21 km stretch of close proximity to
reduce the potential of bigheaded carps entering the CSSC from the Des Plaines River during
flooding (USACE 2010a).
Similarly, the I&M Canal connects to the CSSC downstream of the Lockport Lock and Dam. The
I&M Canal flows intermittently and there is a small drainage divide that sends water toward the
Cal-Sag Channel upstream of the electric dispersal barrier. This divide could be overtopped
during flooding such that water from downstream of the electric dispersal barrier could move
upstream of the electric dispersal barrier. The USACE has enhanced the divide and plugged
outflows from the I&M Canal into the CSSC upstream of the electric dispersal barrier (USACE
2010a).
The USACE also has installed screens on its sluice gates at the O’Brien Lock and Controlling
Works (USACE 2010b). The USACE also recommended that the Metropolitan Water
Reclamation District of Greater Chicago install screens on the sluice gates of the Chicago River
Controlling Works and to modify operations at the Wilmette Pumping Station for diversion water
intake if requested (USACE 2010b).
Another possible pathway for moving past the electric dispersal barrier is movement of small
bigheaded carps in leaking barges. Reports of barges pumping water from void spaces are
common throughout the Illinois Waterway, including the CSSC. To investigate this potential, a
study to investigate the efficacy of bigheaded carp transport by barges was conducted (Heilprin
et al. 2011). This study of water quality in barge voids found that dissolved oxygen levels and
water temperatures were well within limits for fish survival, even during the hot months of the
year (Heilprin et al. 2011). In 2011, attempts to entrain bigheaded carp larvae into voids by
simulating a punctured barge hull were not successful due to difficulties associated with proper
river conditions and the timing of bigheaded carp spawning, but survival of bigheaded carp
larvae in cages within void spaces was high (Heilprin et al. 2011). This study also found that
10
survival of larval and small bigheaded carps (< 80 mm TL) was unlikely when passed through
pumps commonly used on barges to remove water from voids.
2.1.1.2 Other Connections
The USACE is conducting a five year Great Lakes – Mississippi River Interbasin Study
(GLMRIS) to comprehensively analyze the options, technologies, and alternatives for preventing
the interbasin transfer of aquatic nuisance species between the two basins (USACE 2011a).
The study, led by the USACE with a variety of other American agencies, is divided into two
focus areas: one examining options for the CAWS; and, a second focus area that examines 19
potential natural and artificial hydrologic connections between the basins. The connection
through the CAWS is considered higher risk within the GLMRIS study than the remaining 18
connections examined in Focus Area 2. Of these 18 possible connections, the authors felt three
had stronger hydrological connections with implications for bigheaded carps: 1) Eagle Marsh in
Indiana; 2) Ohio-Erie Canal in Ohio; and, 3) the Libby Branch connection to Lake Superior
(Figure 5).
Figure 5. Identified hydrological connections for aquatic invasive species transfer between the Mississippi
River and Great Lakes basins. Map courtesy of U.S. Army Corps of Engineers.
The Eagle Marsh in northwestern Indiana is an area that joins the Wabash River system with
the Maumee River system under some flood conditions. This site has been rated the highest
risk of aquatic invasive species transfer among the 18 locations evaluated in Focus Area 2 of
GLMRIS. Bighead Carp have been reported about 35 km (22 river miles) downstream of Eagle
Marsh in the Wabash River (USACE 2010b). One dam upstream of Huntington IN on the Little
River (an older fixed crest approximately 2 m high) stands between bigheaded carps and
eventual arrival in the Eagle Marsh area. Indiana deployed a large-mesh fence to deter
movement of adult fishes between the two basins. During spring 2011 flooding, adult Common
Carp attempted, but were not able, to cross this fence.
There is potential for bigheaded carps, should they move from the Ohio River up the
Tuscarawas River, to enter the Lake Erie drainage from Long Lake into the Ohio-Erie Canal and
11
from there into the Little Cuyahoga River. The connection points are only 91 m from each other
across a 1.5 m embankment (USACE 2010b). Bigheaded carps are known to be in the Ohio
River at Pittsburgh, PA. It is unclear if these fishes originated in the area from a release or if
they made their way up the river through Ohio (John Navarro, Ohio Department of Natural
Resources, pers. comm.). The Tuscarawas River is a tributary of the Muskingum River and
connects to the Muskingum River above Coshocton, Ohio. The start of the Tuscarawas River is
about 161 km from the Ohio River and there are eight dams on the lower Muskingum River
between the Ohio River and the Tuscarawas River. The head of these dams range from 3.5 7 m; therefore, it would be very difficult for bigheaded carps to make it up to this area (John
Navarro, Ohio Department of Natural Resources, pers. comm.), but should they make it there,
the connection to the Lake Erie drainage is close.
Another connection identified in the GLMRIS project as high risk for aquatic invasive species
transfer was the Libby Branch connection to Lake Superior; however, this connection is
characterized by many dams that would inhibit the dispersal of bigheaded carps past these
barriers.
There are many ponds and artificial lakes in the Chicago metropolitan area. They are commonly
stocked for fishing with Channel Catfish (Ictalurus punctatus). Channel Catfish are often
purchased from southern fish farmers, where it is possible for the stock to be contaminated with
small Bighead Carp. For instance, in September 2011, 17 large Bighead Carp were collected
from Flatfoot Lake in the Beaubien Forest Preserve (K. Irons, Illinois Department of Natural
Resources, pers. comm.). Flatfoot Lake is located about 180 m from the Calumet River,
downstream of the O’Brien Lock and Dam. Three Bighead Carp were also found from Schiller
Pond. Neither of these waterbodies have a direct connection to either Lake Michigan or the CalSag Channel, but escapes of another Asian carp, Grass Carp, have occurred in similar
circumstances (Maceina et al. 2011).
While it is unclear if any of these ponds could connect with the Lake Michigan watershed during
flooding events, it does provide a source of individuals in close proximity for illegal movement
(see Section 2.1.2).
Since its opening in 1959, the St. Lawrence Seaway/River continues to be an important route
for the introduction of aquatic invasive species, such as the copepod, Eurytemora affinis, and
White Perch (Morone americana) (Scott and Christie 1963, Hebert et al. 1989). Should
bigheaded carps gain access to the St. Lawrence River, this would provide a direct route to
Lake Ontario.
Unlike the ballast water in freighters that originate outside of the Great Lakes-St. Lawrence
River basin, ballast water in freighters that remain in the basin (known as “lakers”) is not treated
for AIS in any way (see Section 2.4.1.3 for more details). If bigheaded carps were to become
established first in the St. Lawrence River, laker movement may facilitate the arrival of the
species into the Great Lakes basin. Over 2 million metric tonnes (mt) of ballast water is taken in
by lakers in St. Lawrence ports each year (Table 4). This ballast water was transported primarily
to other ports in the St. Lawrence River, and lakes Superior, Erie, Ontario, Huron and Michigan
(Figure 6 - see also Section 2.4.1.3).
12
Table 4. Estimated ballast water transfer volumes between basins associated with commercial laker
traffic based on data used in Rup et al. 2010. Annual average volume (mt) data are provided as received
and donated by a Great Lake and the St. Lawrence River. A small fraction (< 2.5%) of trips from Rup et
al. (2010) were excluded due to uncertain ballasting procedures as were transfers within a basin.
Basin
Erie
Huron
Michigan
Ontario
St. Lawrence
Superior
Annual Average (mt)
Recipient
Donor
3,114,797 27,806,506
8647344 12,792,195
7,166,444 19,975,152
1,139,413
5,338,245
2,956,685
2,883,148
35,212,014
1,772,893
Figure 6. Destination of ballast water discharge for trips originating from any port within St. Lawrence
River. Annual averages and standard deviations of ballast discharge volumes, 2005 – 2007, are
summarized from Rup et al. (2010).
2.1.2 Human-mediated Release
The potential for purposeful, human-mediated releases of bigheaded carps into the Great Lakes
basin does exist. Humans have illegally released freshwater fishes for sport opportunities
(Crossman and Cudmore 1999a, Bradford et al. 2008) or spiritual/ethical reasons (Crossman
and Cudmore 1999b, Severinghaus and Chi 1999, Shiu and Stokes 2008). This human
behavior of illegally releasing nonnative fishes into the aquatic environment is difficult to
characterize and quantify (Bradford et al. 2008). For this reason, we are unable to qualify the
risk of intentional release, but should note its existence as a potential source of introduction of
13
bigheaded carps into the Great Lakes basin. Within this risk assessment, we assessed the
human-mediated release from bait use and from trade.
2.1.2.1 Bait
The live baitfish pathway is a potential entry route for the arrival of small bigheaded carps into
the Great Lakes. Baitfishes are used for angling in all states and provinces surrounding the
Great Lakes, although specific regulations and the degree of baitfish activity vary by
state/province (Table 5). The term ‘baitfish’ generally refers to a variety of small fishes with
species dependent on local regulations, supply, and angler preference. Within most Great
Lakes jurisdictions, baitfish supply may occur through angler self-harvesting (i.e., angler capture
of small baitfishes using minnow traps, seines, or dip nets) or baitfish may be commercially
harvested or cultured. Although culture does not occur within Great Lakes jurisdictions due to
limited growing seasons, cultured baitfishes from American states outside of the basin (e.g.,
Arkansas, parts of Minnesota, North Dakota, South Dakota; Gary Whelan, Michigan DNR, pers.
comm.) may be transported to Great Lakes states for sale to retailers and anglers. It is illegal to
bring in live baitfish from the U.S. into Canada. Following harvest or culture, baitfishes are
purchased by anglers at angling retail stores or, in the case of self-harvest, are transported
directly to the angling destination. Despite legislation, anglers may release undesirable or leftover baitfishes into the destination waterbody following angling (Litvak and Mandrak 1993;1999,
Dextrase and MacKay 1999, Kulwicki et al. 2003, Drake 2011), although the prevalence of
release may be declining (A. Drake, DFO, unpubl. data).
Table 5. Summary of 2011 recreational angling regulations for states and provinces in the Great Lakes
basin related to potential Asian carp entry through the baitfish pathway. Although each jurisdiction has
specific movement regulations (e.g., certain significant waterbodies may exhibit no-baitfish rules to
protect sensitive game stocks), movements listed below concern noteworthy baitfish movement
restrictions within each jurisdiction as they relate to pathway operations and the potential for Asian carp
movement or entry into the pathway. In many cases, generic restrictions against ‘carp’ (presumably
Common Carp) were made; these are listed simply as ‘carp’ unless specifically defined as Asian carps.
State / Province
Minnesota
Wisconsin
Illinois
Indiana
Regulation
(Possession / Use)
General white list (list of species
permissible to use), with prohibition on
using whole or parts of ‘Carp’ for bait
(MNDNR 2011; p. 11). Specific
prohibition about possessing or
transporting Asian carps (MNDNR 2011;
p. 10).
General white list allows for all species
in the minnow family, but with specific
prohibition against ‘Carp’ (WDNR 2011;
p. 7, 14).
Generic list of legal baitfish species;
includes ‘minnows’ but does not
specifically preclude ‘Carp’ (ILDNR
2010; p. 2).
Generic list of legal baitfish species;
specific prohibition against ‘Carp’ (IDNR
2011; p. 2).
14
Regulation
(Movement)
Statewide movement restrictions
in response to viral hemorrhagic
septicemia (VHS) concerns;
anglers required to exchange bait
water when leaving infected zone.
Species-specific regulations (e.g.,
Alewife restrictions within Great
Lakes) govern most statewide
movement restrictions.
Few statewide restrictions to
baitfish movement.
Few statewide restrictions to
baitfish movement.
Michigan
White list of legal baitfishes, with
specific prohibition against Asian carps
and other known invaders (MDNR 2011;
p. 6, 14-15).
Ohio
White list of legal baitfish species;
prohibits use of fish species that are not
already established in Ohio waters
(ODNR; 2011).
General use of baitfishes allowed; the
use or possession of Common Carp as
baitfish while fishing is prohibited (PFBC
2011; p. 7, 30).
Green (list of species permissible to
use) list of legal species for widespread
angler use in the state. Additional list of
species for use in waters only where
currently found (e.g., Alewife in Great
Lakes). ‘Carp’ collection or use as bait is
prohibited. (NYDEC 2011; p. 19-20).
Pennsylvania
New York
Québec
Ontario
Very limited use of live baitfishes is
allowed. Where allowed, only native
species may be used; collection or use
of ‘Carp’ and non-indigenous fish
species for bait is prohibited
(Ressources naturelles et faune Québec
2011; p. 8-9).
White list of baitfish species; specific
prohibition of use and possession of
Asian carps (OMNR 2011; p. 8-10).
Movement zones vary in
response to VHS concerns;
movement to outside of GL
drainages generally restricted or
reduced.
Generally, movement of baitfish
out of Lake Erie drainage
prohibited in response to VHS
concerns.
Certain baitfish species prohibited
from movement out of Lake Erie
drainage in response to VHS
concerns.
Commercial catch VHS-free
certification process determines
the degree of allowable
movement. Uncertified bait (some
commercial catches and all selfharvested fishes) may not be
transferred overland and must be
used at point of harvest.
Substantial restrictions to baitfish
movement, with use limited to a
very few waterbodies exhibiting
strict species regulations.
Restricted movement of Great
Lake commercial baitfish catches
to inland waters in response to
VHS concerns; anglers
encouraged to comply with
commercial movement
restrictions.
The likelihood of the baitfish pathway as an entry route for bigheaded carps is dependent upon:
1) the distribution and intensity of baitfish harvest activity in relation to the distributional cooccurrence of bigheaded carps and target baitfishes in the wild; 2) the ability of commercial
harvesters, baitfish retailers, and anglers to effectively sort or ‘cull’ bigheaded carps
(presumably juveniles) from target catches; and, 3) the nature and prevalence of angling
activities (e.g., long-distance transport and corresponding baitfish release) that allow for
bigheaded carp entry into the Great Lakes basin.
All states and provinces within the Great Lakes basin designate certain baitfish species, usually
deemed to be of low ecological risk, for angling use. Species listings provide a legal mechanism
to prohibit the capture, use, and movement of invasive fishes, such as bigheaded carps, during
baitfish operations. For example, in Ontario, a list of allowable target baitfishes legally precludes
15
undesirable species from the pathway (OMNR 2011). Yet, because the industry in Ontario and
other jurisdictions within the Great Lakes basin rely on wild harvest, potential for non-target fish
by-catch exists. A recent study of the Ontario baitfish pathway indicated the existence of
invasive and other non-target fish by-catch during baitfish harvest operations in Great Lakes
nearshore waters and tributaries (Drake 2011).The prevalence of invasive and other non-target
fishes within retail tanks and angler purchases was generally much lower than that of harvest
operations, indicating a substantial degree of species culling following harvest. However, even
low prevalence of non-target species in angler purchases was sufficient for non-target species
introductions, as low prevalence was offset by a large number of angler trips (4.12 million yearly
events involving live fishes) (Drake 2011). The spatial distribution of live bait angling events in
Ontario indicated that even the shortest trips involving live baitfishes were sufficient to surpass
drainage basin boundaries, with the longest trips further emphasizing spread potential (Drake
and Mandrak 2010).
Using results from a study (Drake 2011) of the baitfish industry and AIS in Ontario suggest that
the entry route of bigheaded carps into the Great Lakes basin through the baitfish pathway will
be largely dependent on the specifics of baitfish activity within each jurisdiction such as:
characteristics of harvest activity in relation to bigheaded carp source populations; angler use,
movement patterns, release rates; and, the yearly volume and spatial distribution of angling
events within and outside of the Great Lakes basin.
Most states prohibit the use of “carp” as baitfish with Michigan and Ontario specifically
prohibiting the use of “Asian carps” (Table 5). Most states and Ontario have restrictions on the
within-jurisdiction movement of baitfishes, with Ontario prohibiting the importation of baitfishes
(Table 5). For most jurisdictions, knowledge is lacking about: the degree to which these
regulations are followed; which bait originates in areas of bigheaded carp populations; angler
use, movement, and release patterns; and, annual volume and distribution of angling events.
A survey of bait shops in the Chicago area was conducted in 2010 to determine presence of
bigheaded carps in bait tanks using both visual and eDNA surveillance methods (Jerde et al.
2012). Fifty-two bait shops in nine northeastern Illinois counties were assessed. Visual
inspections and eDNA water samples (n = 136 from 94 bait tanks) were conducted. No Bighead
or Silver carps were observed or detected by visual inspections or eDNA analysis. Although this
study provided no evidence that bigheaded carps are part of the Chicago area bait trade, it was
a brief snapshot in time.
2.1.2.2 Trade
Bigheaded carps, which are listed under the injurious wildlife provisions of the Lacey Act,
cannot be legally imported into the United States or moved interstate live without a permit. Since
2005, the eight Great Lakes states have amended their rules and regulations to prohibit
movement and/or possession of live bigheaded carps across their jurisdictions. Even with these
regulations, enforcement could be improved, given that live Bighead Carp were transported
through U.S. states before these fishes were seized in Canada in 2010-2011 (see below).
In Canada, there is no federal legislation in place regarding import of aquatic species that may
pose an invasion risk. At the time this risk assessment was written, the Province of Quebec did
not have provincial regulations regarding prohibition of possession or sale of live Asian carps.
The Ontario Ministry of Natural Resources (OMNR) banned the live sale of Asian carps through
the Fish and Wildlife Conservation Act in 2004 and banned the live possession of Asian carps
through the Ontario Fishery Regulations in 2005.
16
Prior to these rules and regulations being developed by Great Lakes jurisdictions, some
individuals of Bighead Carp were caught in Lake Erie (see Cudmore and Mandrak 2011). The
body condition of these individuals was healthy, but for those individuals dissected, their
reproductive organs were not viable (B. Cudmore, Fisheries and Oceans, pers. comm.). It is
likely these individuals were released from the live food trade prior to 2004, but there is no
evidence that Bighead Carp established in Lake Erie (Cudmore and Mandrak 2011). Therefore,
with the removal of these few non-reproductive individuals, the invasion process would be
considered reset back to ‘pre-arrival’ for the Great Lakes.
Caution must be used with analyzing import records into Canada. For January 1, 2010 to
August 17, 2011 data, only Harmonization System codes were available, which group live fish
imports into very broad categories. Importers are relied upon to accurately place their imports
into the correct categories; however, during border inspections of live aquatic species into
Toronto and Niagara Falls, several discrepancies were noted among import records, import
invoices, and the actual specimen/commodity being imported (B. Cudmore, N. Mandrak, DFO,
pers. obs.).
Importation records of fishes entering Canada must be considered with caution. For January
2010 through August 2011, 11,573 import transactions for live fishes were recorded by Canada
Border Services Agency (CBSA) across Canada. 73.2% of total live fishes imported into
Canada were for aquarium or ornamental purposes, while 26.8% were imported for food. Of the
26.8% destined for the live food industry, 81.7% came from the United States (B. Cudmore,
unpubl. data).
The United States was the primary exporter of all fishes to Canada (72.3% of total live fishes
imported). The majority of these fishes were exported from California (31.9%), Florida (26.3%),
Arkansas (4.9%), Pennsylvania (4.0%), and North Carolina (3.7%). Of the live fishes exported to
Canada, most were imported into Ontario (46.7%) followed by British Columbia (18.7%), Alberta
(16.5%), and Quebec (13.2%) (Figure 7) (B. Cudmore, unpubl. data).
Proportion of Canadian import volume
(%)
50
40
30
20
10
0
ON
AB
QC
BC
Other
Province
Figure 7. Proportion of total import of live fishes into Canada, by province (2010-2011), recorded by port
of entry, as reported by Canada Border Services Agency. ON=Ontario; AB=Alberta; QC=Quebec;
BC=British Columbia
17
Species-specific information is lacking with the 2010-2011 data; however, there is a category for
‘carp’ that importers were relied upon to use for all carp species, including bigheaded carps.
Florida is responsible for exporting 23% of the total live carp into Canada, with Indiana (16.2%)
and Arkansas (10.3%) representing other significant states of export.
Of the 46.7% of total live fishes imported into Ontario, 4.95% were represented by ‘carp’.
Primary entry locations into Ontario included Toronto Pearson International Airport (23.4% of
Canadian imports, 50.1% Ontario imports), Niagara Falls-Queenston Lewiston Bridge (11.1%
Canadian imports, 23.7% Ontario imports), and Windsor-Ambassador Bridge (5.8% Canadian
imports, 12.3% Ontario imports) (B. Cudmore, unpubl. data).
Food industry import shipments are often, but not always, reported as units of weight in the
shipping transaction. From January 1, 2010 to August 17, 2011, import data using weight
indicate that approximately 13,774 metric tonnes (mt) of aquatic organisms classified as ‘live
fish’ were imported into Canada (B. Cudmore, unpubl. data). Of this, 872 mt were classified as
‘carp’. Border officials identified a further 19 mt as “probable carp”, meaning imports that were
not officially classified as carp but had carp in their "additional info/species" field. Therefore, we
can surmise from this information that, in total, 891 mt of ‘carp’ were reported as imported into
Canada. Live fishes classified as ‘carp/probable carp’ were imported into Ontario (840 mt) for
food and aquarium and Alberta (50 mt) for aquarium (Figure 8). Most of these carps would most
likely be Common Carp or koi.
Percentage (%)
60
40
20
0
ON
AB
QC
BC
MB
SK
NS/NL
NB/PEI
Canadian Province
Proportion of total fish imported into province
Proportion carp of total import into province
Proportion of Grass Carp of total carp by province
Proportion of Bighead Carp of total carp by province
Figure 8. Proportion of live fishes, “carps”, Grass Carp and Bighead Carp imported into Canada by
province/region. From B. Cudmore, unpubl. data; ON=Ontario; AB=Alberta; QC=Quebec; BC=British
Columbia; MB=Manitoba; SK=Saskatchewan; NS/NL=Nova Scotia/Newfoundland and Labrador;
NB/PEI=New Brunswick/Prince Edward Island.
It is currently illegal to possess or sell live Asian carps in Ontario; however, despite this
legislation, Bighead Carp and Grass Carp were documented in shipments for import into
Ontario. Eight entry records were recorded from January 2010 to August 2011 that listed Grass
18
(9.8 mt) and Bighead (16.8 mt) carps as species descriptions. All of the shipments originated in
Arkansas.
Some illegal shipment attempts into Ontario have been stopped by Canadian enforcement
officers. In November 2010, there was a seizure at the Bluewater Bridge, Sarnia of 1,136 kg of
Bighead Carp and 727 kg of Grass Carp after officers from both Canada Border Services
Agency and OMNR inspected incoming shipments of live and fresh fishes (Sean Insley, OMNR,
pers. comm.). In March 2011, a Markham (near Toronto, Ontario) fish importer was fined
$50,000 for transporting live Bighead Carp (nearly 2,500 kg) from the U.S. across the WindsorDetroit border. A few days later, an Indiana company, caught bringing live Bighead Carp (2,727
kg) into Canada, was fined $20,000. All fishes originated in Arkansas and were headed to live
fish markets in the Toronto area (Sean Insley, OMNR, pers. comm.).
Feeder fishes (typically Goldfish (Carassius auratus) or “rosy reds” (colour variant of Fathead
Minnow (Pimephales promelas)) shipped into the Great Lakes basin could be contaminated with
bigheaded carps if they originated from fish farms in the Mississippi River basin. Fathead
Minnows found in the bait industry in Michigan are known to originate from culture in Arkansas,
Minnesota, North Dakota, and South Dakota (Gary Whelan, Michigan DNR, pers. comm.).
However, the volume of such movement and the extent of contamination, if any, is unknown.
Based on a subsample of live fish import records for 2006-2007, Fathead Minnows (likely rosy
reds) imported for the aquarium trade originated primarily from Missouri and secondarily from
North Carolina (B. Cudmore, DFO, unpubl. data).
The possession and sale of live Asian carps within the province of Quebec is currently legal, but
prohibition regulations were recently posted for public consultation. However, import records
into Canada (B. Cudmore, unpubl. data) indicate that carps are not entering into the province in
large numbers (Figure 8).
2.1.3 Summary of Likelihood of Arrival
In summary, two pathways of potential entry into the Great Lakes basin were identified and
assessed: physical connections; and, human-mediated release (Table 5). For this risk
assessment the invasion process is considered at ‘pre-arrival’ for the Great Lakes. With the
removal of a few individuals over the past decade and positive eDNA samples, there is no sign
the invasion process has moved to the next phases.
The most likely point of direct arrival into the Great Lakes basin is through the CAWS to Lake
Michigan due to the proximity of established and invading bigheaded carp populations, the
presence of positive eDNA samples, and the capture of one live Bighead Carp in the area
above the electric dispersal barrier (Table 6).
Other physical connections to the Great Lakes basin were identified and ranked low, with the
exception of Lake Superior, which was ranked very unlikely (Table 6). Of the hydrological
connections considered high risk for aquatic nuisance species transfer (GLMRIS 2011), only
one, Eagle Marsh IN, was considered by the authors as a high potential for bigheaded carp
transfer to the Great Lakes (to Lake Erie). Eagle Marsh provides conditions suitable for
bigheaded carp movement and is in proximity to bigheaded carp populations. However, this
area is not suitable for spawning; therefore, the potential movement is limited to adults only.
Direct transfer to the Great Lakes basin from the Chicago area ponds would be difficult due to
the lack of natural connections. Also, fewer catfish farmers are raising Bighead Carp since the
species was listed as ‘injurious’ under the Injurious Wildlife provisions of the Lacey Act. The Act
19
prohibits interstate transport of live Bighead Carp. Therefore going into the future, new
stockings would have lowered potential for contamination. Sampling within the CAWS, both by
eDNA and traditional sampling methods, provide for the ability to detect bigheaded carps early
in the invasion process. Currently there are no bigheaded carps in or near the St. Lawrence
River. Should they gain access to the St. Lawrence River, laker ballast water or natural
dispersal would provide a direct route to Lake Ontario. However, the opportunities for the
introduction of bigheaded carps to the St. Lawrence River are not well understood. Certainty for
all lakes for physical connections was moderate, with the exception of Lake Michigan (high).
Potential for movement from the Mississippi River to the Great Lakes basin varies for each lake
with respect to the human-mediated release pathway (Table 6). Variation in regulations for bait
use and movement, as well as trade opportunities does vary by lake. In Lake Superior, it is very
unlikely this pathway is of strong importance given the distance from established bigheaded
carp populations and the time it will take before young specimens (e.g., from bait) could be
found in nearby areas. There is also no international trade of bigheaded carps identified with the
Lake Superior watershed. Lake Michigan was ranked low for human-mediated release; higher
than for Lake Superior given the proximity of established populations as a source of available
individuals. Lakes Huron and Ontario are associated with a low risk, taking into consideration
the lack of movement of bait and trade from bigheaded carp areas and these lakes. However,
these lakes are exposed to stronger fisheries from American anglers compared to Lake
Superior, and Lake Ontario is also the location of live markets that could be involved in illegal
trade. The risk of direct arrival to Lake Erie is also low, taking into consideration the presence of
a higher number of anglers in lakes St. Clair and Erie, the frequent use of live bait in the area,
and the potential for accidental release from illegal shipping of bigheaded carps coming from
Windsor towards Toronto. Certainty associated with human-mediated releases varies by lake
from low to moderate.
Table 6. Overall probability of introduction rankings and certainties for each lake. Overall arrival is the combination of
physical connections and overall human-mediated release. Greyed cells indicate “not applicable”. (CAWS=Chicago
Area Waterway System)
Superior
Michigan
Huron
Erie
Ontario
Element
Rank
Cert Rank Cert
Rank
Cert Rank Cert Rank Cert
Very
CAWS
High
Likely
Very
Other Connections
Low
Mod
Mod
Low
Mod
Unlikely
Very
Very
Overall Physical
Low Mod
Mod
High
Unlikely
Likely
Connections
Bait
Trade
Overall HumanMediated Release
OVERALL ARRIVAL
(Combined Overall
Physical
Connections and
Overall Humanmediated Release)
Very
Unlikely
Very
Unlikely
Very
Unlikely
Very
Unlikely
Low
Low
Low
Low
Low
Low
Low
Low
Low
Mod
Low
Mod
Very
Unlikely
Low
Low
Low
Low
Mod
Low
Low
Low
Low
Low
Low
Low
Low
Low
Mod
Very
Likely
High
Low
Low
Low
Mod
Low
Mod
20
2.2 LIKELIHOOD OF SURVIVAL
The likelihood of survival (does not die upon arrival and lives over winter months) of bigheaded
carps was based on available scientific knowledge of these species’ biological requirements in
terms of food resources and thermal tolerance, and the availability of such conditions within the
Great Lakes basin.
At least three large adult Bighead Carp have been captured live from Lake Erie (Kolar et al.
2007, Cudmore and Mandrak 2011). Those fish are unlikely to have been recent escapes from
aquaculture or live food trade because their size at capture (606 to 937 mm; Morrison et al.
2004) was much larger than the size at which cultured fish are harvested for sale (Engle and
Brown 1999). Condition factor of those fish was extremely high (based on lengths and weights
from Morrison et al. 2004). Aging structures from those fish indicated that the fish were growing
rapidly (Morrison et al. 2004) and showed an early life history consistent with an aquaculture
origin. It is clear that these fish were surviving and growing very well in Lake Erie. A live
Bighead Carp was also captured from Lake Calumet, a portion of the CAWS, and environmental
DNA from both Bighead and Silver carps has been collected from this system (USACE 2011b).
While this particular habitat is not representative of the Great Lakes as a whole, it should be
noted that the Great Lakes are not a uniform habitat and a variety of habitat types exist in all of
the lakes. Bigheaded carps are mobile fishes (DeGrandchamp et al. 2008) and capable of
selecting habitat types conducive to their survival.
2.2.1 Food Resources
A bioenergetics model (Cooke and Hill 2010) suggested that bigheaded carps could survive in
Lake Erie and in some embayments of the remaining Great Lakes, but that planktonic resources
would be insufficient to support growth of Bighead and Silver carps in the open waters of the
larger Great Lakes. Further research to refine and evaluate that model has been performed and
continues at the time of this writing. Recently completed, but unpublished, data on Bighead
Carp (K. Massagounder, Univ. of Missouri, pers. comm.) indicates that the Cooke and Hill
(2010) model appears to overestimate growth at high food abundances and underestimate
growth at low food abundance. Error rates were higher at the higher food abundances than at
low food abundances, and higher at warmer temperatures (>18°C) than at cooler temperatures.
This recent research indicates that respiration/maintenance costs used in the model are higher
than measured costs, and that energy content of bigheaded carps is substantially lower than
that used in the model. It is unclear at this time whether these improvements to the Cooke and
Hill (2010) model would substantially increase the zones where bigheaded carps could survive,
but they clearly support the conclusion that sufficient planktonic food exists in parts of the Great
Lakes to provide for their survival and growth.
The degree to which non-planktonic sources of food in the Great Lakes may enhance survival of
bigheaded carps is unclear but, in some cases, alternative foods may allow survival of
bigheaded carps in regions where planktonic resources are inadequate. Bigheaded carps are
primarily filter-feeders on plankton, but they are known to consume detritus (Anwand and
Kozianowski 1987, Chen and Liu 1989, Cremer and Smitherman 1980, Takamura 1993). In
studies in Dagestan, Russia (Lazareva et al. 1977) and in the lower Missouri River (D.
Chapman, U.S. Geological Survey, pers. obs.) where planktonic food sources were in short
supply, detritus often constituted more than 90% of the diet. However, the value of detritus as a
food source for bigheaded carps is unclear and is probably highly variable depending on the
origin of the detritus. Takamura (1993) found that detritus enriched by Grass Carp feeding was
sometimes an important source of food for Silver Carp, but Lin et al. (1981) found that detritus
21
formed by the degradation of Microcystis aeruginosa (a blue-green algae common in the Great
Lakes) was not an adequate diet to support growth of bigheaded carps. In addition, the
energetic demands of detrital feeding, compared to pelagic filtering, are not understood, and
may vary depending on detritus or substrate type. Nevertheless, the fact that bigheaded carps,
at times, consume substantial detritus leads to the conclusion that they can benefit from the
behaviour. Consumption of detrital food would open larger parts of the Great Lakes to invasion
by bigheaded carps or allow bigheaded carps to disperse across areas with less than adequate
planktonic resources.
Two likely sources of enriched sediment detritus in the Great Lakes are dreissenid mussel feces
and pseudofeces and attached algae such as Cladophora and Lyngbia. Dreissenids remove
plankton and organic material from the water and excrete feces and pseudofeces that collect in
depositional areas (D. Chapman, USGS, unpubl. data). Attached algae have become more
abundant in the Great Lakes because of increased water clarity and enhanced available
inorganic nutrient concentrations resulting from dreissenid feeding on plankton (D. Chapman,
USGS, unpubl. data). These attached algae break from their attachments and can become a
part of the detritus. Studies on the nutritional value of enriched sediment detritus in the Great
Lakes are incomplete at the time of this writing, but may also contribute to the survival or
dispersal of bigheaded carps.
2.2.2 Thermal Tolerance
The Asian range of Bighead and Silver carps extends northward to the Amur River basin (Kolar
et al. 2007). Bighead Carp are not thought to be native to the Amur basin, but they are present
and established there. Herborg et al. (2007) compared environmental characteristics (including
temperature) between the Asian range and North America, and found that the entire Great
Lakes region, as well as a large portion of Canada, was well within the potential range of both
species (Figure 9).
2.2.3 Summary of Likelihood of Survival
Information on food availability and thermal tolerance was used to assess the likelihood of
survival of bigheaded carps in each of the Great Lakes. Alternative foods may allow for survival
when planktonic food sources are inadequate. Modeling of environmental characteristics from
the native range of bigheaded carps indicates that there is a strong match to environmental
characteristics in the Great Lakes. For all lakes, likelihood of survival was ranked very likely with
high certainty (Table 7). The certainty exception being for Lake Erie (very high) due to the
greater volume of research associated with that lake in particular, and the existing records of the
capture of healthy Bighead Carp individuals in this lake, thereby, indicating proven ability to
survive in Lake Erie.
22
a
b
Figure 9. Potential distribution of a) Bighead Carp (Hypophthalmichthys nobilis) and b) Silver Carp (H.
molitrix) in North America based on environmental suitability, or the number out of a maximum of 100
niche-based models that predicted a certain area as appropriate. Modified from Herborg et al. (2007).
Table 7. Likelihood of survival rankings and certainties for each lake.
Element
Survival
Superior
Rank Cert
Very
High
Likely
Michigan
Rank Cert
Very
High
Likely
Huron
Rank Cert
Very
High
Likely
Erie
Rank
Cert
Very
Very
Likely
High
Ontario
Rank Cert
Very
High
Likely
2.3 LIKELIHOOD OF ESTABLISHMENT
Assessment of the likelihood of establishment (evidence of the ability to reproduce, which would
lead to a self-sustaining population) assumes that arrival and survival have occurred, and that
the number of adult bigheaded carps present in the system is sufficient for spawning to
potentially occur. The establishment of bigheaded carps in the Great Lakes would then be
23
dependent upon availability of suitable spawning and nursery habitats, survival of early life
stages, stock size required for effective recruitment, and positive population growth.
2.3.1 Spawning and Nursery Habitat
A study of Silver Carp indicated they seem to require an average of 2,685 total annual degreedays (ADD; sum of mean daily water temperatures for all days above 0oC) each year over
several years to mature (Krykhtin and Gorbach 1981). In a northern native population, males
matured at 4-10 years and females at 6-10 years (Gorbach and Krykhtin 1981 in Naseka and
Bogutskaya 2011), which incorporates delay of maturity up to 2 year in the coldest years
(gorbach and Krykhtin 1980 in Naseka and Bogutskaya 2011). In North America, maturity was
reached in 2-3 years (Kipp et al. 2011). Once mature, bigheaded carps required a minimum
number of total annual degree-days based on water temperature above 15oC to reach spawning
condition: 655 ADD for onset of spawning; and, 933 ADD for mass spawning (Gorbach and
Krykhtin 1981 in Naseka and Bogutskaya 2011). Bigheaded carps are only known to spawn in
rivers and it is believed that a rising hydrograph (flood event) is a primary spawning cue (Kolar
et al. 2007). In its native range, Bighead Carp has a fecundity ranging from 280,000-1.1 million
eggs (Kolar et al. 2007). In North America, fecundity ranged from 4,792-1.6 million eggs (Kipp et
al. 2011). In its native range, Silver Carp has a fecundity ranging from 299,000-5.4 million eggs
(Kolar et al. 2007). In North America, it has ranged from 26,650- 3.7 million eggs (Kipp et al.
2011).
Once the eggs are released and fertilized, the semi-buoyant, fertilized eggs may need to remain
suspended in current until they hatch (Kolar et al. 2007). Hatching time is related to temperature
(Kolar et al. 2007 and references therein). Larvae move to productive habitats (e.g., wetlands)
for feeding and/or protection (Kryzhanovsky et al. 1951, Abdusamadov 1987, D. Chapman,
unpub. data).
Bigheaded carp spawning has been documented to occur in tributaries generally longer than
100 km (Krykhtin and Gorbach 1981, Kolar et al. 2007). Kolar et al. (2007) identified 22
American tributaries of the Great Lakes that were unimpounded from the mouth to at least 100
km upstream to lakes Superior (three tributaries), Michigan (seven tributaries), Huron (four
tributaries), and Erie (eight tributaries). There were no tributaries identified by Kolar et al. (2007)
for Lake Ontario. Cudmore and Mandrak (2011) identified over 80 Canadian tributaries to the
Great Lakes that were unimpounded from the mouth to at least 50 km upstream (Superior (30
tributaries), Huron (28), Erie (9), Ontario (19)). Fifty-two Canadian tributaries are unimpounded
from the mouth to at least 80 km upstream (Superior (22 tributaries), Huron (16), Erie (6),
Ontario (8)), and forty-one tributaries to at least 100 km upstream (Superior (16 tributaries),
Huron (14), Erie (5), Ontario (6)) (Mandrak et al. 2011). The shortest flowing body of water in
which bigheaded carps are known to have spawned is in an 87-km reach of the Kara Kum
Canal in Turkmenistan (Aliev 1976).
Two recent studies have examined the suitability of Great Lakes tributaries for bigheaded carp
spawning based on more detailed considerations of reproductive biology. Kocovsky et al. (2012)
examined eight American tributaries in the central and western basins of Lake Erie. They
considered: the thermal conditions of the tributaries and Lake Erie, the minimum total degreedays required for maturation, onset of spawning and mass spawning, timing of flood events as
triggers for spawning, and length of stream required for egg hatching based on stream velocity
and estimated incubation time. They concluded that the three larger tributaries were thermally
and hydrologically suitable to support spawning of bigheaded carps, four tributaries were less
suited, and that one was ill suited. Mandrak et al. (2011) conducted a similar analysis for the
24
Canadian tributaries of the Great Lakes. They concluded suitable spawning conditions were
present in nine of 14 tributaries to Lake Superior with sufficient data; however, only one of the
nine tributaries had a mean annual total degree-days exceeding 2,685. Therefore, bigheaded
carps are unlikely to mature within Lake Superior tributaries, but may encounter sufficient
growing degree-days to mature in some parts of Lake Superior such as near shore and bays.
Further analysis is required to identify such areas. Mandrak et al. (2011) concluded suitable
spawning conditions, including growing degree-days required for maturation, were present in 23
of 27 tributaries to Lake Huron, nine of 10 tributaries to Lake Erie, and 16 of 28 tributaries to
Lake Ontario. Neither Kocovsky et al. (2012) nor Mandrak et al. (2011) incorporated the scale
(e.g., minimum stream width) and nature of spawning habitat (e.g., turbulence) because the
detailed characteristics required for bigheaded carp spawning are poorly understood.
Furthermore, these studies rely on velocity measurements at few locations and are thus coarse
drift models. More precise modeling would require extensive field data that are currently
unavailable. Similar studies have not been conducted for US tributaries in lakes Michigan,
Huron, Superior, Ontario, nor the eastern basin of Lake Erie, but the analyses of Kocovsky et al.
(2012) and Mandrak et al. (2011) suggest that access to tributaries with suitable thermal and
hydrologic regimes in the Great Lakes should not limit spawning by bigheaded carps.
A particle tracking model and estimated incubation times were used to examine the spawning
suitability of St. Clair and Detroit rivers (N. Mandrak, Fisheries and Ocieans, unpubl. data). The
model indicated that fertilized eggs in the St. Clair River would be deposited in Lake St. Clair
before hatching, and those in the Detroit River would be deposited in Lake Erie before hatching.
As there are no verified records of bigheaded carp eggs hatching in lentic waters and the
currents of lakes St. Clair and Erie are generally less than 0.1m/s (Ibrahim and McCorquodale
1985; Leon et al. 2005), the eggs would likely not survive. The potential for lentic spawning (i.e.,
where eggs fall to substrate) is a knowledge gap that needs to be further investigated,
particularly for locations with strong currents, clean substrates, and few Round Goby
(Neogobius melanostomus) populations (e.g., Lake Superior). These results may be
conservative as Chapman and George (2011) developed models showing faster hatching rates
and hatching success on sediment.
Cudmore and Mandrak (2011) concluded that there were ample wetlands throughout the Great
Lakes basin, including those associated with unimpounded tributaries greater than 50 km, which
would be suitable nursery habitats for bigheaded carps. Mandrak et al. (2011) similarly
concluded that many of the Canadian tributaries with suitable spawning habitat for bigheaded
carps also had suitable nursery habitat. Although not assessed for suitability as nursery habitats
for bigheaded carps, numerous coastal wetlands also exist throughout the Great Lakes in the
United States (Simon and Stewart 2006).
2.3.2 Estimated Spawning Population Needed for Establishment
Because no data are available on the number of bigheaded carps needed to establish a
population, it was assumed for the purposes of this risk assessment that sufficient numbers of
adult bigheaded carp were present to potentially spawn. However, managers at a workshop
held in November 2010 to identify management questions of concern asked to know the
number of bigheaded carps needed to establish a population. Currie et al. (2011) addressed
this question by modeling the probability of successful spawning of bigheaded carps in the
Great Lakes based on a small founder population using a variant of the ‘birthday problem’
(Wendl 2003). They modeled the probability of successful spawning in three scenarios: (1)
assuming bigheaded carps use environmental cues to identify rivers suitable for spawning, that
once in a river, pheromone cues make encounter between male and female unproblematic, fish
25
are ready for spawning at about the same time, and several suitable spawning rivers are
available and found by fish; (2) assuming that not all fish present in the lake arrive at suitable
spawning rivers (i.e., fish have some difficulty in locating rivers); and, (3) assuming variability
about spawning time of individuals. Common assumptions across scenarios are a 1:1
male:female sex ratio, spawning could occur between one male and one female, and suitable
conditions for spawning occurred each year (i.e., hydrographs were conducive to spawning).
They concluded that when adults were able to accurately cue into suitable rivers for spawning, a
founder population of 10 females and 10 males had a greater than 50% chance of successfully
spawning. The minimum number of bigheaded carp required to have a 50% chance of
spawning increased to 20 mated pairs if maturation time varied, or if fish only had a 20%
success rate at choosing suitable spawning rivers. Similarly, number of fish required further
increased if there was a larger number of suitable rivers, or if the fish have difficulty finding
suitable spawning rivers. When factors that would limit successful spawning were combined,
such as bigheaded carps being unable to accurately distinguish between suitable and
unsuitable rivers, and that they must be present in a river over a very short time interval, the
expected probability of a spawning was small. Multiple spawning events can occur in a given
year, however, if hydrologic conditions are conducive (Papoulias et al. 2006).
2.3.3 Survival of Early Life Stages
High fecundity, as found in bigheaded carps, is typically associated with high mortality in early
life stages (Kolar et al. 2007). To date, there have been no specific studies on mortality rates of
early life stages of bigheaded carps. Survival would be related to feeding, predation, and
overwinter mortality. Newly hatched bigheaded carp larvae can move vertically and, as a result,
do not need to remain in the current (Chapman and George 2011). Given high fecundity rates,
they would encounter high intraspecific competition likely resulting in an initial high densitydependent mortality. Competition for food resources with other species has not been studied for
early life stages, but is highly likely not to be limiting given the success of bigheaded carps in
the Mississippi River watershed.
Bigheaded carp larvae in the drift that are younger than the gas bladder inflation stage do not
appear to strongly avoid capture by nets or siphon tubes, and thus probably have poor predator
avoidance strategies (D. Chapman, USGS, pers. obs.). However, older larvae did strongly
attempt to avoid aquarium nets and siphon tubes. At that age, larvae begin to move toward
wetland nursery habitats where they would be less susceptible to pelagic ichthyoplanktivores
(D. Chapman, USGS, unpublished data.). However, there have not been any North American
studies of predation on bigheaded carp juveniles (Kipp et al. 2011). Given the high fecundity
strategy of the bigheaded carps and that most native species must go through a similar
predation-prone period, it is unlikely that such predation would limit bigheaded carp population
growth. Bigheaded carps undertake rapid growth, with Bighead Carp averaging 273 mm at age1 (back calculated) and Silver Carp averaging 318 mm at age-1 in the Mississippi River (Nuevo
et al. 2004). Growth would likely be slower in the Great Lakes and, even if the growth was 33%
slower within their first year, the bigheaded carps would quickly exceed the gape size of most
fish predators in the Great Lakes.
Overwinter mortality is an important limiting factor in temperate fishes (e.g., Shuter et al. 1980).
It can typically result from prolonged starvation or extended periods of low dissolved oxygen
concentrations (known as winterkill), the latter not typically occurring in the Great Lakes and its
tributaries. Overwinter mortality as a result of starvation occurs when, going into their first
winter, fishes have insufficient energy reserves (typically correlated to size) to survive until
26
resources become available the following spring (Holm et al. 2009). Because overwinter
mortality is correlated to length of winter, it becomes more important with increasing latitude. It
is not known to be an issue for bigheaded carps in the Mississippi River basin; bigheaded carp
fingerlings are collected from floodplain wetlands in the spring in years when those wetlands
were not connected to the river (D. Chapman, USGS, pers. obs.). Overwinter mortality may
influence the northern limits of the native range of bigheaded carps, but has not been modelled
specifically for these species in North America. However, ecological niche modeling based on
their native range would implicitly incorporate such mortality. Ecological niche modeling
predicting the potential North American distribution of bigheaded carps indicated that they could
survive well north of the Great Lakes basin (Herborg et al. 2007); therefore, overwinter mortality
will likely not be a limiting factor in most years.
2.3.4 Stock Required for Effective Recruitment
No data was located on stock size for effective recruitment of bigheaded carps in environments
similar to the Great Lakes. A stock-recruitment model has been developed, however, for
Bighead Carp in large rivers of the United States. The Asian Carp Working Group (2007) of the
Aquatic Nuisance Species Task Force recommended development of stock-recruitment models
for Bighead Carp and other Asian carps to assist in management and control of feral
populations. Hoff et al. (2011) developed a Ricker stock-recruitment model using Bighead Carp
population data collected in the LaGrange Reach of the Illinois River and Pool 26 of the
Mississippi River during 2001-2004 to guide management and control efforts there. The
modeled functional relationship explained 83% of the recruitment (during July through October
of the first year of life) variation using stock size and river discharge (Figure 10). Seventy-two
percent of recruitment variation was explained by stock-size abundance, while an additional
11% was explained by the coefficient of variation of discharge in July. Assuming the stockrecruitment relation in the Illinois and Mississippi rivers is similar to one that would develop in
the Great Lakes, the risk of establishment of Bighead Carp, and probably Silver Carp, would
increase rapidly with small increases in adult stock size (Figure 11).
27
Figure 10. Functional relationship, from the trivariate stock-recruit model for Bighead Carp, of recruitment
to stock size abundance and river discharge coefficient of variation during July. From Hoff et al. (2011).
Figure 11. Empirical stock and recruitment data and the stock-recruit model for Bighead Carp in the
LaGrange Reach of the Illinois River and Pool 26 of the Mississippi River, 2001-2004. From Hoff et al.
(2011).
28
2.3.5 Positive Population Growth
Population growth and establishment models are lacking in the literature for bigheaded carps.
The need for such modeling was identified at a workshop attended by those conducting
research on bigheaded carps in November 2010. Currie et al. (2011) developed stagestructured deterministic and stochastic population growth models for bigheaded carps in the
Great Lakes under various scenarios to fill this information gap.
The deterministic model incorporated four life stages: juvenile (eggs, larvae, Age-0); first
subadult stage (Age-1); second subadult stage (Age-2); and adult (Age-3+) and was
parameterized using data from the literature where available. Once a stable stage distribution
was reached, the model predicted large population growth rate (λ) of λ=2.18 per year. A second
version of the model was developed with sexual maturity at age 5 rather than age 3. Using this
model, the annual population growth rate was slower (λ=1.36). In both versions of the model,
population growth was most sensitive to the survivorship of juveniles followed by those in the
first subadult stage.
The stochastic model incorporated environmental stochasticity (years with poor reproductive
success), likelihood of adults finding a suitable spawning river, and variation in number of initial
females (10-30) and spawning rivers (1, 5, and 10). The model predicted the probability of
population establishment (population size of 1000 adult females within 20 years) and growth
under three release scenarios (where the number of fish released varied from 2-60): a single
release of adults; a single release of subadults; and a slow release of subadults. Currie et al.
(2011) conservatively assumed mated pairs of males and females and one spawning event per
season. The model predicted that under the worst-case scenarios (maturity at 3 years and a
high ability to locate suitable spawning rivers) as few as 10 mated pairs of bigheaded carps
present in one Great Lake would result in a very high probability of establishment in that lake
within 20 years. This probability was lower and the number of fish required was higher for a
single release of subadults than the other two scenarios. Probability of establishment decreased
and time to establishment increased if fish cannot accurately identify suitable spawning rivers..
For example, the probability of establishing a population within 20 years in a Great Lake under a
low probability of finding a spawning river varied between 0 and 35% as the number of
spawning rivers varied (see Figure 3-3 in Currie et al. 2011). Models predicted substantially
longer than 20 years to establishment regardless of number of spawning pairs, spawning rivers,
or environmental stochasticity if age at maturity was raised from 3 to 5 years (see Figure 3.4 in
Currie et al. 2011).
2.3.6 Summary of Likelihood of Establishment
Research on the establishment of bigheaded carps indicates lakes Huron, Erie, and Ontario
have suitable spawning tributaries based on thermal and hydrologic regimes, some of which
have adjacent suitable nursery habitat. Nine tributaries were identified in the Lake Superior
basin with amenable hydrologic regimes; however only one was sufficiently warm. The ability for
bigheaded carps to mature in the Lake Superior basin needs to be examined further. Thermal
and hydrologic regimes of potential spawning tributaries of Lake Michigan have not been
examined, but Lake Michigan does have tributaries that exceed 100 km that might have the
minimum requirements for Asian carp spawning and recruitment. Although little published
information exists, competition, predation and overwinter mortality of early life stages would
likely not limit establishment of these species. Little published information exists regarding
population growth for bigheaded carps. A stock-recruitment model suggests that the risk of
establishment may increase rapidly with small increases in adult stock size. Deterministic and
29
stochastic population growth models predicted positive population growth in the Great Lakes,
but that it would be slower if fish reached sexual maturity at age 5 rather than age 3. In the
scenarios examined, the most conservative likelihood of establishment was estimated to be
100% with 10 mated pairs of a species of bigheaded carp in a single Great Lake basin (given a
single release of adult fish and high ability of fish to locate appropriate tributaries for spawning).
Time to population establishment wass dependent upon age of maturity and was likely to be
relatively short (i.e., within 20 years) in the southern portion of the Great Lakes basin.
Given that access to suitable spawning and nursery habitat should not be limiting, nor should
survival of early life stages, the high likelihood of recruitment and positive population growth, the
likelihood of establishment for all but Lake Superior was ranked very likely with high certainty. It
is likely that age of maturity will be older in Lake Superior and that establishment would take
longer. Given the likely older age of maturity, fewer suitable spawning tributaries, and
uncertainty related to ability to mature in the Lake Superior basin, the likelihood of
establishment for Lake Superior was ranked moderate with moderate certainty (Table 8).
Likelihood of establishment for the rest of the Great Lakes was ranked very likely with high
certainty.
Table 8. Likelihood of establishment rankings and certainties for each lake.
Superior
Rank
Cert
Michigan
Huron
Erie
Ontario
Element
Rank Cert Rank Cert Rank Cert Rank Cert
Very
Very
Very
Very
Establishment Moderate Moderate
High
High
High
High
Likely
Likely
Likely
Likely
2.4 LIKELIHOOD OF SPREAD
Following successful establishment within the Great Lakes basin, the likelihood of spread into
other areas of basin was assessed based on the best available scientific information about
dispersal (i.e., volitional swimming of individual fish, through canals or via ballast water) or
human-mediated vectors (i.e., baitfish introductions). Ballast water is considered in spread with
dispersal rather than with human-mediated vectors. Subsequently, each of the Great Lakes has
been considered separately since the likelihood of spread via these vectors may differ among
lakes.
2.4.1 Dispersal
2.4.1.1 Natural Dispersal
Few studies have assessed the movement of bigheaded carps in natural environments. Those
that have been completed were conducted in rivers or ponds (Konagaya and Cai 1989, Peters
et al. 2006, Kolar et al. 2007, DeGrandchamp et al. 2008), habitats that differ significantly from
those available in much of the Great Lakes basin. Movement rates of bigheaded carps reported
from riverine telemetry studies have varied. Peters et al. (2006) conducted telemetry of Bighead
Carp on the Illinois River (May-July 2003 and 2004) and found a mean movement rate of 1.7
km/day but, in some cases, individual fish moved longer distances (up to 14 km/day). Kolar et
al. (2007) reported results of a telemetry study of Bighead Carp in the Missouri River that found
individual Bighead Carp did not travel long distances (<15 km) except during high water where
some fish moved more than 80 km. DeGrandchamp et al. (2008) conducted telemetry on
Bighead Carp and Silver Carp in the lower Illinois River during spring-summer 2004 and 2005
using mobile and stationary receivers and found that Bighead Carp moved a mean of 3.6
km/day while Silver Carp moved an average of 3.2 km/day. Further, results from stable carbon
30
isotope analysis of otoliths of bigheaded carps by Ernat et al. (2010) suggested that individual
fish inhabiting the area below the electric dispersal barrier moved long distances, originated
from within the Illinois River, the middle Mississippi River, and floodplain lakes along the lower
Illinois River valley. Because of a lack of information from the peer-reviewed literature on natural
movement of bigheaded carps via natural dispersal in lacustrine environments, we must rely on
modeling efforts to predict potential spread through the Great Lakes by this vector.
Two studies have been completed to date that address potential spread of bigheaded carps in
the Great Lakes. Currie et al. (2011) assessed the potential spread of bigheaded carps from
various entry points around the Great Lakes using the Fish Foraging and Movement model, an
individual-based, Markov process movement model. The model allowed habitat use to be
affected by zooplankton abundance and distribution and current patterns (i.e., fishes would stay
in more profitable areas longer before moving on) and simulations were run for 1, 2, 5, 10, and
20 years. Cooke and Hill (2010) developed bioenergetics models for bigheaded carps based on
empirically derived parameters from the literature. They assessed the potential of bigheaded
carps to colonize habitats in the Great Lakes based on plankton biomass and surface water
temperature data. Their models indicated that many open-water regions of the Great Lakes
could not support growth of bigheaded carps. The models indicated, however, that more
productive regions, such as Green Bay, western Lake Erie, and some other wetlands and
embayments, did contain sufficient planktonic resources. It is noteworthy that this study was
based solely on empirically derived data and considers only plankton as food resources for
bigheaded carps (and does not include many rotifers which are known to be important in the
diets of bigheaded carps; Bardach et al. 1972; Berday et al. 2005). Results of these studies are
discussed below as they apply to individual Great Lakes.
2.4.1.2 Canals
Studies are largely lacking that quantify the movement of invasive species through canals, as
well as lock and dam structures. Brooks et al. (2009) implanted several fish species, including
bigheaded carps, with sonic tags from 2006 through 2008 to assess passage of fishes through
the Lock and Dam complexes of the Upper Mississippi River System using stationary data
logging receivers. They documented both upstream and downstream passages of bigheaded
carps through each Lock and Dam complex from 19 (Keokuk, IA) through 26 (Alton, IL). See
also work by Knights et al. (2003) documenting upstream fish passage at dams. Sauger
(Sander canadensis) (Pegg et al. 1997) and Silver Carp (Calkins et al. 2011) have been
documented moving through lock structures.
Artificial waterway connections, canals, are known to be important pathways that facilitate the
spread of AIS between waterbodies (Mandrak and Cudmore 2010). Sea Lamprey (Petromyzon
marinus), Alewife (Alosa pseudoharengus) Bigmouth Buffalo (Ictiobus cyprinellus), and White
Perch (Morone americana) are examples of species that expanded their range to the upper
Great Lakes through the Welland Canal, the portion of the St. Lawrence Seaway connecting
Lake Ontario to Lake Erie (Mandrak and Cudmore 2010).
2.4.1.3 Laker Ballast
Unlike the ballast water in freighters that originate outside of the Great Lakes-St. Lawrence
River basin, ballast water in freighters that remain in the basin (known as “lakers”) is not treated
for AIS. Therefore, lakers may facilitate the movement of organisms between ports and Great
Lakes, particularly small early life stages such as eggs, larvae, and juveniles. To date, there
have been no quantitative studies on the role of laker ballast water specific for the movement of
fishes, including bigheaded carps. Therefore, findings of Rup et al. (2010) were used as a
surrogate for potential propagule pressure between lakes. To determine the potential for
31
between-lake ballast movement, primary port-to-port trips (i.e., single trips involving a single
ballast-in ballast-out sequence) were plotted by Rup et al. (2010) for each donor region. Trips
display annual average ballast volume (mt) and variability (standard deviation) received at the
port level and originating from each donor region (Figure 12). To describe overall lake-wide
patterns of ballast movement, the annual average and proportion of ballast water transferred
from each donor region was calculated (Table 9). All analyses describing directional ballast
movement, volume and variability were based on data from Rup et al. (2010), describing all joint
American and Canadian laker traffic within the Great Lakes-St. Lawrence River basin, 2005–
2007. A small fraction (< 2.5%) of trips was excluded due to uncertain ballasting procedures.
Ports in lakes Erie, Michigan, and Huron are the greatest donors of ballast water to ports in the
other lakes, and ports in lakes Superior, Michigan, and Huron are the greatest recipients of
ballast water from ports in the other lakes (Table 4).
2.4.2 Human-mediated Dispersal
If bigheaded carps became established in some portion of the Great Lakes basin, their spread
to other areas of the basin could be facilitated by human-mediated dispersal mechanisms. For
the purposes of this risk assessment, baitfish introductions are the only mechanism of humanmediated dispersal that can be qualified.
32
a
b
c
d
e
Figure 12. Destination of ballast water discharge for trips
originating from any port within a) Lake Superior, b) Lake
Michigan, c) Lake Huron, d) Lake Erie, and e) Lake
Ontario. Annual averages and standard deviations of
ballast discharge volumes, 2005 – 2007, are summarized
from Rup et al. (2010).
33
Table 9. Origin of ballast water discharge for trips between Great Lakes and the St. Lawrence River.
Annual averages of ballast discharge volumes, 2005 – 2007, summarized from Rup et al. (2010). A small
fraction (< 2.5%) of trips from Rup et al. (2010) were excluded due to uncertain ballasting procedures.
Recipient
Region
Superior
Michigan
Huron
Erie
Ontario
St. Lawrence
Donor
Region
Superior
Michigan
Huron
Erie
Ontario
St. Lawrence
Total
Superior
Michigan
Huron
Erie
Ontario
St. Lawrence
Total
Superior
Michigan
Huron
Erie
Ontario
St. Lawrence
Total
Superior
Michigan
Huron
Erie
Ontario
St. Lawrence
Total
Superior
Michigan
Huron
Erie
Ontario
St. Lawrence
Total
Superior
Michigan
Huron
Erie
Ontario
St. Lawrence
Total
34
Recipient
Annual
Average
(mt)
1,461,949
11,444,781
8,443,756
12,518,207
1,343,321
290,411
35,502,425
55,607
5,039,678
1,046,856
1,941,544
123,051
6,564
8,213,300
205,391
3,050,252
2,906,624
5,194,303
290,418
50,608
11,697,596
49,945
414,114
347,734
7,917,597
2,159,917
143,088
11,032,394
0
11,589
7,800
180,490
827,523
123,599
1,151,002
0
14,738
39,425
54,366
594,016
2,268,879
2,971,423
Recipient
Proportion
0.041
0.322
0.238
0.353
0.038
0.008
1
0.007
0.614
0.127
0.236
0.015
0.001
1
0.018
0.261
0.248
0.444
0.025
0.004
1
0.005
0.038
0.032
0.718
0.196
0.013
1
0.000
0.010
0.007
0.157
0.719
0.107
1
0.000
0.005
0.013
0.018
0.200
0.764
1
There is the potential for bigheaded carps, if they arrive in the Great Lakes basin, to be spread
through the use of baitfish (see Section 2.1.5 for discussion of baitfishes as an arrival route). For
most jurisdictions, knowledge is lacking on the degree to which these regulations are adhered
and to which baitfish originated in areas of bigheaded carp populations, on angler use,
movement, and release patterns, and on annual volume and distribution of angling events. A
recent study (Drake 2011) examined these issues in Ontario and can be used to assess the
potential spread of bigheaded carps through baitfish in the Great Lakes basin (see Section
2.1.2.1 for details).
2.4.3 Lake Superior
2.4.3.1 Natural Dispersal
If bigheaded carps colonized Lake Huron, individuals could disperse through the St. Marys
River, passing its locks and compensating works, to reach Lake Superior. Several invasive
fishes, including Alewife, Sea Lamprey, White Perch, and Rainbow Smelt (Osmerus mordax)
have used the St. Marys River to colonize the lake (Mandrak 2009). Nonnative fishes initially
found only in Lake Superior (Fourspine Stickleback (Apeltes quadracus), Ruffe
(Gymnocephalus cernua)) have not yet colonized other Great Lakes naturally from Lake
Superior, and have yet to be found in proximity to the St. Marys River; therefore, they are not a
good test as to whether fishes can colonize Lake Huron from Lake Superior through natural
dispersal. In Lake Superior, tagged Lake Trout (Salvelinus namaycush) have been known to
leave the lake through the St. Marys River within a year (M. Hoff, USFWS, pers. comm.).
Modeling by Currie et al. (2011) predicted that given an entry point into the Great Lakes of the
CAWS, very few bigheaded carps would make it to Lake Superior in 20 years, but those that did
would be attracted to northern embayments, including Black and Thunder bays and the
western-most arm near the St. Louis estuary. No bigheaded carps were predicted to enter Lake
Superior within 20 years when the entry point was in lakes St. Clair or Erie. When the starting
point was western Lake Superior, bigheaded carps tended to remain in that region because of
higher production, but were also attracted to Black and Thunder bays and the Keweenaw
Peninsula. However, this model does not take into account characteristics of the system that
may serve as an attractant for bigheaded carps, such as turbulence of the St. Marys River;
therefore, the Currie et al (2011) results may underestimate visits over time to Lake Superior.
Bioenergetics modeling by Cooke and Hill (2010) predicted a maximum travel distance in 30
days for Bighead and Silver carps to be 0.8-7.5 and 2.1 km, respectively (predicted movement
was dependent on location of colonization and size of individual).
Given that lock and dam structures in the St. Marys River did not inhibit the movement of several
invasive fishes, such as Alewife, Sea Lamprey, White Perch, and Rainbow Smelt from Lake Huron to
Lake Superior (Mandrak 2009) and that bigheaded carps have been documented to move upstream
and downstream through lock and dam structures (Brooks et al. 2009), it is not expected that these
structures would impede the movement of bigheaded carps to or from Lake Superior. Likely, the
turbulence of the area may serve as an attractant for bigheaded carps to move towards Lake
Superior.
Based on the analysis of ballast water from lakers presented from Rup et al. (2010), Lake
Superior is primarily a recipient of inter-lake ballast water, with a high proportion of ballast it
receives deriving from lakes Michigan, Erie, and Huron (Table 9). The two nonnative fishes,
Fourspine Stickleback and Ruffe, initially found only in Lake Superior, are thought to have
arrived in ballast water (Mandrak and Cudmore 2010). The larger ports in Lake Superior are
also those likely to contain sufficient planktonic resources to sustain bigheaded carps (Cooke
35
and Hill 2010); therefore, these ports may also serve as sources for potential spread by interlake ballast water, should early life stages of bigheaded carps be present.
2.4.3.2 Human-mediated Dispersal
Lake Superior was the sixth most popular destination for Ontario anglers using live baitfishes
(Drake 2011). These baitfishes would originate primarily from the Canadian nearshore waters
and tributaries of lakes Huron, Erie, and Ontario, and secondarily from inland lakes in southern
Ontario (Drake 2011).
2.4.4 Lake Michigan
2.4.4.1 Natural Dispersal
Several invasive fishes have spread to Lake Michigan from adjacent Great Lakes (e.g., Alewife,
Sea Lamprey, White Perch). In addition, Rainbow Smelt have spread from the Lake Michigan
basin to other Great Lakes (Stewart et al. 1981). Also, models by Beletsky et al. (2007)
indicated small fishes are transported by currents of the lake; Yellow Perch larvae were
transported from southwestern Lake Michigan to Traverse Bay in approximately 2-3 months. If
bigheaded carps were present in Lake Michigan, they could disperse into Lake Huron via
natural dispersal through the Straits of Mackinac. Likewise, if they were present in Lake Huron,
they would have access to Lake Michigan.
As discussed in 2.1.1.1, the CAWS and surrounding waterways are potential sites of bigheaded
carp introduction into the Great Lakes basin. Currie et al. (2011) modeled the potential spread
of bigheaded carps with an entry site into Lake Michigan at the CAWS. Models predicted that
the most likely sites in Lake Michigan that would attract bigheaded carps in the first five years
after introduction would be the Muskegon River, Grand Traverse Bay, and Green Bay. Predicted
potential spread after 20 years, with introduction at the CAWS, varied with parameters
describing movement of individual fish, but included lakes Huron and Erie in the default model
tested. After influences of food limitation and currents were added into the model, lakes Huron,
Erie, and either Ontario or Superior were predicted to be visited by bigheaded carps, depending
on fish movement rates. Lake Michigan was predicted to not be visited by bigheaded carps
within 20 years of introduction when entry points were modeled from lakes Erie (including Lake
St. Clair) or Superior. Bioenergetics modeling by Cooke and Hill (2010) predicted relatively high
maximum distance traveled over 30 days from Green Bay, compared with other Great Lakes
areas (27.0-33.4 km for 10 g and 28.8-35.0 km for 2,400 g Bighead Carp; 29.8-31.4 km for 10 g
and 22.8-24.4 km for 2,400 g Silver Carp, in spring and summer).
Lake Michigan is not connected to other Great Lakes by artificial waterways. Therefore, if
bigheaded carps become established in some portion of the Great Lakes, they could not spread
to or from Lake Michigan via artificial pathways.
Based on the analysis of ballast water from lakers presented in Rup et al. (2010), Michigan
ports are the second leading donor of laker ballast water to the other Great Lakes (Table 4).
Western Lake Superior, northern Lake Michigan, and northern Lake Huron are the destinations
receiving the greatest volume (Figure 12). The proximity of bigheaded carps to the southern
basin of Lake Michigan and the high proportion of inter-lake ballast derived from this lake
contribute to risk of spread via this pathway should bigheaded carps become established in port
areas of Lake Michigan . Lake Michigan ports receive the third greatest amount of lake ballast
water, primarily from Lake Erie ports (Table 4).
36
2.4.4.2 Human-mediated Dispersal
No studies on angler behavior related to baitfish movement along the coasts of Lake Michigan
were identified.
2.4.5 Lake Huron
2.4.5.1 Natural Dispersal
Several invasive fishes have spread to Lake Huron from adjacent Great Lakes (e.g., Alewife,
Sea Lamprey, White Perch, Rainbow Smelt). If bigheaded carps were present in Lake Huron,
they could likely disperse through the St. Marys River to Lake Superior or through the Detroit
River, Lake St. Clair, and the St. Clair River to Lake Erie. Similarly, it is expected that bigheaded
carps present in either Lake Superior or Lake Erie could move via natural dispersal into Lake
Huron.
Using an introduction point at the entrance to the CAWS, dispersal modeling by Currie et al.
(2011) predicted that 30-50% bigheaded carps would visit Lake Huron within 10 years of
introduction under each set of model simulation assumptions. Also given this introduction point,
those models predicted that bigheaded carps would be attracted to Saginaw Bay and the North
Channel of Georgian Bay five years after introduction, across the range of swimming speeds
and lake current influence.
The Fish Movement Model in Currie et al. (2011) suggested approximately 5% (± 2%) of
bigheaded carps were predicted to enter Lake Huron by year 2 when the starting point was
Lake St. Clair. This was under conditions where swimming rates were 14 cm/s and a 25%
influence of lake currents. Under slower movement rates, this 5% value was reached in 5-10
years. If the fishes ignore lake currents or swim against flow, a slightly higher percentage of
fishes enter Lake Huron. Cooke and Hill (2010) did not include analysis of Lake Huron in their
study.
Given the historical use of the St. Marys River by invasive fishes to spread from Lake Huron to
Lake Superior (Mandrak 2009) and the documented upstream and downstream movement of
bigheaded carps through locks (Brooks et al. 2009), it is not thought that these connecting
waters would impede movement of bigheaded carps in either direction.
Based on the analysis of ballast water from lakers presented in Rup et al. (2010), Lake Huron
donates more inter-lake ballast water than it receives (Table 4), but the destination of about a
quarter of the laker ballast water derived from Lake Huron is received by ports within that same
lake (Table 9). Lake Superior is the major recipient of laker ballast from Lake Huron, followed by
Lake Michigan (Table 9, Figure 12). Lake Huron ports receive the second greatest amount of
lake ballast water, primarily from ports in lakes Erie, Michigan, and Huron (Table 9).
2.4.5.2 Human-mediated Dispersal
Lake Huron and Georgian Bay ranked, respectively, the third and fifth most popular destinations
for Ontario anglers using live baitfishes (Drake 2011). These baitfishes would originate primarily
from the Canadian nearshore waters and tributaries of lakes Erie, Huron and Ontario, and
secondarily from inland lakes in southern Ontario (Drake 2011).
37
2.4.6 Lake Erie
2.4.6.1 Natural Dispersal
The connecting channels between Lake Huron and the western basin of Lake Erie (St. Clair
River, Lake St. Clair, and the Detroit River) would not impede the spread of bigheaded carps
from one lake to the other; this pathway has previously been used by invasive fishes to move
between basins (e.g., Alewife, Sea Lamprey, White Perch, and Rainbow Smelt). Instead, the
warm and productive waters of the Huron-Erie Corridor may act as attractants for bigheaded
carps and facilitate further dispersal.
Using an introduction point at the entrance to the CAWS, modeling by Currie et al. (2011)
predicted that bigheaded carps would visit Lake Erie within 20 years of introduction under each
set of model simulation assumptions. Models also predicted that Lake St. Clair, the western
basin of Lake Erie, and Sandusky Bay could become potential sites for establishment, but that
almost every location in Lake Erie would be suitable for bigheaded carps. Given, instead, an
entry point of bigheaded carps into Lake St. Clair, fishes remained primarily in Lake Erie
because of the high abundance of food resources; although, by 20 years, there were visits to
lakes Huron and Ontario. Similarly, given an entry point of bigheaded carps into the Great
Lakes at the mouth of the Maumee River, models predicted that bigheaded carps would remain
primarily in Lake Erie, with some visits to Lake Ontario by 20 years after introduction. Overall,
Cooke and Hill (2010) predicted bigheaded carps could swim greater maximum distances in the
western basin of Lake Erie without losing biomass than other areas simulated in the Great
Lakes. In the western basin, maximum distances that could be traveled were higher in the
spring (26.7-33.7 km) than summer (3.9-14.8 km). Predicted maximum distances traveled
before beginning to lose mass in the central and eastern basin were similar to those of the
western basin in the summer.
Although movement rates of fishes through the Welland Canal have not been studied, this route
has resulted in the establishment of fishes from Lake Ontario into Lake Erie (e.g., Sea Lamprey,
and White Perch). Preliminary results of a study on the movement of fishes in Welland Canal
lock chambers using hydroacoustics, conducted in October 2011, indicated that there were
many small and large fishes present (N. Mandrak, unpubl. data) further suggesting that fishes
likely move directly through the Welland Canal. Given that bigheaded carps have been
documented to move upstream and downstream through lock and dam structures (Brooks et al.
2009), the Welland Canal may slow, but may not curtail, the movement of bigheaded carps
between lakes Erie and Ontario.
Based on the analysis of ballast water from lakers presented in Rup et al. (2010), Lake Erie is
primarily a donor of inter-lake ballast water throughout the basin (Table 4). Lake Erie is the
source of 35-72% of inter-lake ballast for lakes Superior, Huron, and Michigan (Table 9, Figure
12). In addition, 72% of inter-lake ballast received in Lake Erie originates from that same lake
(Table 9). The proximity of bigheaded carps to the Lake Erie drainage, the abundance of food
resources and suitable habitat for bigheaded carps, and the fact that Lake Erie is a source of
much of laker ballast water both within Lake Erie and the other Great Lakes, with western Lake
Superior, northern Lake Huron and Lake Erie ports being the destinations receiving the greatest
volume (Figure 12), contribute toward the risk of laker ballast for spreading bigheaded carps in
the basin. Lake Erie ports receive the fourth greatest amount of lake ballast water, primarily
from ports in lakes Huron and Erie (Table 7).
38
2.4.6.2 Human-mediated Dispersal
Lake Erie and Lake St. Clair ranked, respectively, the second and ninth most popular
destinations for Ontario anglers using live baitfishes (Drake 2011). These baitfishes would
originate primarily from the Canadian nearshore waters and tributaries of lakes Erie, Huron and
Ontario, and secondarily from inland lakes in southern Ontario (Drake 2011).
2.4.7 Lake Ontario
2.4.7.1 Natural Dispersal
The only natural dispersal pathway for bigheaded carps to get from the other Great Lakes into
Lake Ontario is survival over Niagara Falls. No field study of fish survival (of any life stage)
going over Niagara Falls could be located; however, we know of one muskellunge (Esox
masquinongy) that was tagged above the falls in the Niagara River that was recovered below
the falls (K. Kapucinski, SUNY-Syracuse, pers. comm.) and presumably survived going over the
falls. Potential survival of any life stage of bigheaded carps over Niagara Falls remains a
knowledge gap.
Given an introduction point at the entrance of the CAWS, the Fish Movement Model of Currie et
al. (2011) predicted that very few (<2%) bigheaded carps would visit Lake Ontario after 20
years, but those that did would be attracted to sites such as the Genessee River and Bay of
Quinte, under the standard swimming rates of 14 cm/s and a 25% influence of lake currents.
This percentage is higher, and arrival times are earlier, if fishes swimming speed was greater, or
the fishes were more passively transported by lake currents.
Approximately 5% (± 2%) of bigheaded carps were predicted to get to Lake Ontario within 10
years when the starting point was in Lake Erie or Lake St. Clair, using the standard swimming
parameters. When the starting point was Montreal, it took more than 5 years for fishes to arrive
at Lake Ontario under the same model conditions. Relative to the other Great Lakes, Cooke and
Hill (2010) predicted high maximum distances traveled in 30 days without losing biomass in
Lake Ontario. They predicted biomass loss would begin in adult Silver Carp before adult
Bighead Carp in all three areas of Lake Ontario examined (16-21 km and 26-33 km,
respectively).
Although movement rates of fishes through the Welland Canal have not been studied, this
pathway has resulted in the establishment of fishes from Lake Ontario into Lake Erie (e.g., Sea
Lamprey and White Perch). Preliminary results of a study on the movement of fishes in Welland
Canal lock chambers using hydroacoustics, conducted in October 2011, indicated that there
were many small and large fishes present (N. Mandrak, unpubl. data) further suggesting that
fishes likely move directly through the Welland Canal. Given that bigheaded carps have been
documented to move upstream and downstream through lock and dam structures (Brooks et al.
2009), the Welland Canal may not curtail the movement of bigheaded carps between lakes Erie
and Ontario.
According to the analysis of ballast water from lakers presented in Rup et al. (2010), Lake
Ontario donates almost five times the amount of inter-lake ballast water as it receives (Table 4).
Most of the laker ballast from Lake Ontario makes its way to either lakes Erie or Superior,
though some is received at other ports within Lake Ontario (Figure 12). About 72% of laker
ballast coming into Lake Ontario originated within the lake (Table 9). Lake Ontario ports receive
the least amount of lake ballast water from ports in other lakes, primarily from Lake Erie and the
St. Lawrence River (Table 9).
39
2.4.7.2 Human-mediated Dispersal
Lake Ontario was the most popular destination for Ontario anglers using live baitfishes (Drake
2011). These baitfishes would originate primarily from the Canadian nearshore waters and
tributaries of lakes Erie, Huron and Ontario, and secondarily from inland lakes in southern
Ontario (Drake 2011).
2.4.8 Summary of Likelihood of Spread
Based on history of movement of fishes in the Great Lakes, there is evidence that fish move
from lake to lake (both upstream and downstream) (Mandrak and Cudmore 2010). Habitat and
food are two factors to be taken into consideration regarding fish movement, along with
availability of suitable physical routes for movement. As Currie et al. (2011) indicated, there is
little incentive for bigheaded carps to move themselves from locations with suitable habitat and
sufficient food abundance. For lakes Superior and Ontario, spread to and from these lakes are
similar, being at the upstream-most and downstream-most locations, respectively. It is unlikely
that spread of bigheaded carps to and from these lakes through dispersal will be strongly
limited; however, movement from the central lakes (lakes Michigan, Huron, and Erie) to lakes
Superior and Ontario would be limited by the abundant food source and suitable habitat found in
those central lakes; there would be little incentive to move from these areas.
Inter-lake ballast water transfer and bait movement between lakes are potential vectors of
spread, but likely have low probability of facilitating the movement of bigheaded carps.
For lakes Superior, Michigan, Huron and Erie, likelihood of spread (Table 10) is very likely due
to lack of structures preventing movement to and from these lakes; high for Lake Ontario.
Certainty for all lakes was high.
Table 10. Likelihood of spread rankings and certainties for each lake.
Element
Spread
Superior
Rank Cert
Very
High
Likely
Michigan
Rank
Cert
Very
High
Likely
Huron
Rank Cert
Very
High
Likely
Erie
Rank Cert
Very
High
Likely
Ontario
Rank Cert
High
High
2.5 SUMMARY OF PROBABILITY OF INTRODUCTION
In summary, the likelihood of arrival, survival, establishment and spread of bigheaded carps
within the Great Lakes basin were assessed using the best available information. As the Great
Lakes basin is so interconnected, the overall probability of introduction was ascertained by first
determining the highest ranking between overall arrival and spread (Table 11), then taking this
with the ranks of survival and establishment and using the lowest rank of the three. This is
represented by the following formula:
Probability of Introduction = Min [Max (Arrival, Spread), Survival, Establishment]
The certainty associated with the highest rank was used or, if two or more certainties were the
same, the certainty associated with the highest rank was used.
Probability of introduction (Table 12) was considered to be very likely for lakes Michigan, Huron,
and Erie, high for Lake Ontario, and moderate for Lake Superior, with the level of certainty as
high for all lakes, with the exception of Lake Superior (moderate).
40
Table 11. Maximum rank of overall arrival and spread (Max(Arrival, Spread)) for each lake.
Element
Overall Arrival
Spread
Max(Arrival, Spread)
Superior
Michigan
Huron
Erie
Ontario
Rank
Cert Rank Cert Rank Cert Rank Cert Rank Cert
Very
Very
Mod
High Low Low Low Mod Low Mod
Unlikely
Likely
Very
Very
Very
Very
High
High
High
High High High
Likely
Likely
Likely
Likely
Very
Very
Very
Very
High
High
High
High High High
Likely
Likely
Likely
Likely
Table 12. Overall probability of introduction rankings and certainties for each lake.
Element
Max(Arrival, Spread)
Survival
Superior
Rank Cert
Very
High
Likely
Very
High
likely
Establishment
Mod
Mod
P(Intro)=Min
[Max(Arrival,
Spread), Survival,
Establish]
Mod
Mod
Michigan
Rank Cert
Very
High
Likely
Very
High
Likely
Very
High
Likely
Huron
Erie
Ontario
Rank Cert Rank Cert Rank Cert
Very
Very
High High High
High
Likely
Likely
Very Very Very
Very
High
High
Likely High Likely
Likely
Very
Very
Very
High
High
High
Likely
Likely
Likely
Very
High
Likely
Very
Very
High
High
Likely
Likely
High
High
3.0 MAGNITUDE OF ECOLOGICAL CONSEQUENCES
Kolar et al. (2007) and Kipp et al. (2011) reviewed the effects of bigheaded carps on invaded
environments. Bigheaded carps are capable of inducing -dramatic changes in planktonic
composition. Plankton is the base of the Great Lakes food web, and changes to plankton
composition are likely to have substantial repercussions. A great deal of information is available
on effects by Silver Carp, or Silver and Bighead carps in combination, on plankton. Much less
information is available on the effects of Bighead Carp alone. The most common effect of
bigheaded carp feeding is a strong decline in crustacean zooplankton populations, even though
bigheaded carps are not thought to be primarily crustacean consumers. Kolar et al. (2007)
described the methods by which bigheaded carps can have this effect. Bigheaded carps also
cause substantial changes in phytoplankton composition. This likely occurs from the removal of
larger phytoplankton, which can often lead to an increase in picophytoplankton (0.2-2 μm) and
smaller nanophytoplankton (2-20 μm), which are not susceptible to grazing by Silver Carp.
Bigheaded carp effects on rotifer abundances have been variable, with some studies showing a
decrease in rotifers, but Sass et al. (2010) found an increase in rotifer abundance (possibly due
to release from predation by crustacean zooplankton) after the bigheaded carp invasion into the
Illinois River.
In the United States, where bigheaded carps are established primarily in large rivers and not in
lakes, effects of the bigheaded carp invasion on native species are not fully understood. Effects
on populations of fishes are difficult to document in highly dynamic systems such as large rivers.
Irons et al. (2007) reported that filter feeding fishes of the Illinois River were lower in condition
factor after the bigheaded carp invasion, and Gutreuter et al. (2011) reported that lipids,
41
especially essential Omega-3 lipids, are reduced in pelagic fishes (but not littoral fishes) in
portions of the Mississippi River where bigheaded carps are abundant. Gutreuter et al. (2011)
also reported that reproductive success of Sauger and Bigmouth Buffalo declined substantially
when Silver Carp were abundant. Such perturbations could be expected to have population
effects at some level, but Gutreuter et al. (2011), using long-term monitoring data, did not find
population-level effects on resident fishes of the Mississippi and Illinois rivers that could be
attributed to the bigheaded carp invasion. Populations of large river fishes are highly dependent
on physical variables such as hydrographs, and those variables are likely to mask populationlevel effects.
In lentic systems, undesirable population-level effects of bigheaded carp introductions on native
fishes have often been described in the literature. Effects on native planktivorous fish species
are most commonly described (Spataru and Gophen 1985, Natarajan 1988, Wilkonska 1988,
Shetty et al. 1989, Costa-Pierce 1992, DeIongh and VanZon 1993, Pavlovskaya 1995, Yang
1996, Li 2001, Li and Xie 2002), but some papers have documented effects beyond
planktivores. The International Lake Environment Committee (2001) documented declines in
fish diversity after stocking bigheaded carps and Grass Carp. Costa-Pierce (1992) reported that
Silver Carp introductions into German lakes caused steep declines in populations of several
species with pelagic early life stages, including Zander (Sander lucioperca), a close relative of
the Walleye. In that study, fishes with littoral early life stages were not affected. Svirsky and
Barabanshchikov (2010) noted that at high densities of bigheaded carps in Lake Khanka,
Russia, that reproduction of native pelagic fishes whose eggs develop in the water column was
limited. If bigheaded carps were to become established with abundant populations in the Great
Lakes, they will likely have effects in the lakes similar to the effects that have been documented
worldwide.
3.1 LAKE SUPERIOR
Consequences of established populations of bigheaded carps are projected to include
competition for planktonic food resources, with nearshore, planktivorous fishes in Lake Superior.
That competition may result in reduced growth rates, recruitment, and abundance of Cisco
(Coregonus artedi), Bloater (Coregonus hoyi), and Rainbow Smelt in the nearshore habitats of
Lake Superior. Thus, those species are at risk to become less abundant and grow more slowly
after establishment of bigheaded carp populations in Black Bay, Thunder Bay, Nipigon Bay,
Chequamegon Bay, Whitefish Bay, Keweenaw Bay, the western arm of Lake Superior, and
other nearshore habitats. Reduced abundance of nearshore, planktivorous forage fishes are
projected to result in slower growth, reduced recruitment, and lower abundance of adult
piscivores, such as Lake Trout, that rely on planktivorous forage fishes in nearshore habitats
(Conner et al. 1993, Bronte et al. 2003).
3.2 LAKE MICHIGAN
The food web of Lake Michigan is dominated by pelagic primary production. Since 1995,
dreissenid mussels have increased in abundance exponentially, with maximum densities
recorded at 19,000/m2 in 2008 (Nalepa et al. 2010). Resultant changes in the food web include
a reduced spring diatom bloom (Evans et al. 2011), reduced deep chlorophyll layer (Fahnenstiel
et al. 2010), substantial reduction of Diporeia (Barbiero et al. 2011), and reduced zooplankton
abundance (Johannsson et al. 2000). If the potential impacts of bigheaded carps to the offshore
of Lake Michigan are similar to those predicted for Lake Ontario (see Section 3.5; Currie et al.
2011), bigheaded carps are likely to establish in the offshore of Lake Michigan, but at uncertain
population levels. The resultant impacts to planktivorous fishes can be expected to be generally
42
similar to those in Lake Ontario (see Section 3.5), with Alewife biomass likely being reduced,
with a greater potential for additional top-down reduction of Alewife biomass by the Pacific
salmonine-dominated predator community.
In the nearshore waters of Lake Michigan, it could be expected that Green Bay, southern Lake
Michigan, and the drowned river mouths of the eastern shoreline would be affected more
strongly by bigheaded carps due to the warmer and more productive waters. Bigheaded carp
abundance would likely be higher in these areas, with stronger potential for bigheaded carps to
spawn successfully in one or more tributaries to these areas using spawning tributary
characteristics noted in Kocovsky et al. (2012). Depending on the biomass of bigheaded carps
achieved in these waters, there could be negative effects on fish species such as Yellow Perch
(Perca flavescens) and Lake Whitefish (Coregonus clupeaformis). Nearshore populations of
Alewife also likely would be strongly negatively affected.
3.3 LAKE HURON
Consequences of established populations of bigheaded carps are projected to include
competition for planktonic food resources, with the nearshore, planktivorous fishes in Lake
Huron. That competition may result in reduced growth rates, recruitment, and abundance of
Alewife, Bloater, Cisco, Rainbow Smelt, Yellow Perch, and various centrarchids (Centrarchidae)
in nearshore habitats of Lake Huron. Thus, forage fish stocks are at risk of becoming less
abundant and growing more slowly following the establishment of bigheaded carp populations in
Saginaw Bay, Georgian Bay, the southern basin of Lake Huron, and other nearshore habitats.
Reduced abundance of nearshore forage fishes are projected to result in slower growth,
reduced recruitment, and lower adult abundance of adult Chinook Salmon (Oncorhynchus
tshawytscha), Walleye, Northern Pike (Esox lucius), and Lake Trout stocks that rely on
planktivorous forage fishes in nearshore habitats (Diana 1990, Bence et al. 2008).
3.4 LAKE ERIE (INCLUDING LAKE ST. CLAIR)
Lakes Erie and St. Clair are the warmest and most eutrophic of the Great Lakes, and they are
supplied by rivers such as the Maumee and the Thames, which are possibly the most likely
rivers in this system to provide for spawning and recruitment of bigheaded carps (Kocovsky et
al. 2012; Mandrak et al. 2011). Three individual Bighead Carp have already been demonstrated
to survive and grow rapidly in the western basin of Lake Erie (Morrison et al. 2004). A large
population of bigheaded carps would likely have highly detrimental effects on populations of
planktivorous fishes and fishes with pelagic early life stages such as Walleye and Yellow Perch.
Emerald Shiner (Notropis atherinoides), Gizzard Shad (Dorosoma cepedianum), Rainbow
Smelt, Spottail Shiner (Notropis hudsonius), and White Perch are important planktivorous fishes
of Lake Erie and Lake St. Clair. These species form the majority of the prey base for pelagic
piscivorous fishes, and which would likely decrease in abundance in response to changes in
plankton composition resulting from feeding by bigheaded carps.
Many of these planktivorous species are important prey fishes for Lake Trout, Rainbow Trout
(Oncorhynchus mykiss), Walleye, and Yellow Perch. Loss of prey species would have
undesirable effects on growth and survival of predator species, unless juvenile bigheaded carps
or other species could replace those prey species in the diet of predators. Juvenile bigheaded
carps are not pelagic during the life stages at which they are small enough to be preyed upon
by those pelagic predators (Naseka and Bogutskaya 2011, D. Chapman, USGS, pers. comm),
and so are unlikely to represent an alternative food source. Bigheaded carps also quickly
outgrow the gape size of most native predators in the Great Lakes.
43
3.5 LAKE ONTARIO
The food web of Lake Ontario is dominated by pelagic primary production. Recent food web
changes associated with dreissenid mussels have reduced zooplankton production by about
half between the period 1987-1991 and 2001-2005 (Stewart et al. 2010). This reduction in
zooplankton production is of concern to fishery managers because Alewife, although it can
compensate to a degree for this reduced production by feeding more heavily on Mysis, may be
at greater population risk for overconsumption by salmonines. When considering potential
effects of bigheaded carps on the Lake Ontario ecosystem, preliminary food web modeling
suggests that these invaders can establish in the offshore foodweb (Currie et al. 2011). Under
conditions of low dreissenid mussel biomass, bigheaded carp biomass would increase at the
expense of Alewife biomass; whereas, under conditions of high dreissenid biomass, Alewife
biomass would not decrease to the same degree. Thus, depending on dreissenid biomass, the
establishment of bigheaded carps could reduce Alewife biomass by up to 90%, although the
threat to salmonine populations may not be as strong (see Currie et al. 2011).
3.6 SUMMARY OF MAGNITUDE OF ECOLOGICAL CONSEQUENCES
In Lake Superior, most significant ecological impacts of bigheaded carps are projected in
Thunder Bay, Black Bay, Nipigon Bay, Chequamegon Bay, Keweenaw Bay, Whitefish Bay, the
western arm of Lake Superior, and other nearshore habitats because temperature and food
resources in those locations are most likely to support high-density populations. In Lake
Michigan, current high abundance of dreissenid mussels is projected to result in Alewife
biomass likely being reduced, and a greater potential for additional top-down reduction of
Alewife biomass by the Pacific salmonine-dominated predator community. Fish species in the
nearshore waters of Lake Michigan could be exposed to negative effects considering the high
establishment potential in these areas. In Lake Huron, most significant impacts are projected for
Saginaw Bay, Georgian Bay, the southern basin of Lake Huron, and other nearshore habitats
because temperature and food resources in those locations are most likely to support highdensity populations. In these two Great Lakes, initial impacts are projected to result in
reductions in abundance of nearshore, planktivorous forage fishes. Those reductions are
subsequently projected to result in slower growth, reduced recruitment, and lower abundance of
adult Lake Trout that rely on planktivorous forage fishes in nearshore habitats. In lakes Erie and
St. Clair, a large population of bigheaded carps would likely have highly detrimental effects on
populations of planktivorous fishes and fishes with pelagic early life stages. Loss of prey
species would have undesirable effects on growth and survival of predator species, unless
juvenile bigheaded carps or other species could replace those prey species in the diet of
predators. In Lake Ontario, the impact of bigheaded carps depends on dreissenid biomass. If
such establishment happens, Alewife biomass could be reduced by up to 90%. However, the
threat to salmonine populations may not be as strong.
Overall, with no new additional prevention or management actions, the magnitude of ecological
consequences of a bigheaded carp invasion in the Great Lakes was ranked as moderate for all
lakes over a period of 20 years, with the exception of Lake Superior (low) (Table 13). This
suggests a similar invasion process as what has occurred within the Mississippi River basin
where the consequences of this invasion that started two decades ago is reaching higher levels.
Within 50 years, the magnitude of consequences will be high for all lakes. Certainty for all lakes
in both times periods was ranked as moderate.
44
Table 13. Magnitude of the ecological impacts and certainties to each lake within a 20-year and a 50-year
timeframe.
Element
~20 years
~50 years
Superior
Rank Cert
Michigan
Rank
Cert
Huron
Rank Cert
Erie
Rank Cert
Ontario
Rank Cert
Low
Mod
Mod
Mod
Mod
Mod
Mod
Mod
Mod
Mod
Mod
Mod
High
Mod
High
Mod
High
Mod
High
Mod
4.0 OVERALL RISK ASSESSMENT
As noted in Section 1.1, the overall probability of introduction (Section 2.5) and the magnitude of
the ecological consequences (Section 3.6) were combined to obtain a final risk and was
completed for each lake taking into account both a 20 year (Figure 13a) and 50 year (Figure
13b) timeframe.
5.0 CONSIDERATIONS
Risk assessments are based on best available information, and should identify knowledge gaps
and uncertainties. These knowledge gaps and uncertainties can be reduced through further
research. Prioritized knowledge gaps were compiled by the authors and the peer review
participants and can be found in the proceedings of the peer review (DFO 2012a). Key areas of
uncertainty (where certainty was ranked very low to low) identified in this risk assessment are:
 human-mediated releases into all lakes. This is a key area of uncertainty where more
information and data would strengthen the advice surrounding arrival from this
potential entry route; and,
 overall arrival into Lake Huron.
Risk analysis is composed of risk assessment, risk management, and risk communication
(Mandrak et al. 2012). This risk assessment might be helpful as future mitigation plans for
bigheaded carps are developed. The results of the risk assessment will be communicated with
the public, resource managers, and decision makers in both countries.
Bighead and Silver carps are only two of four Asian carp species that currently threaten the
Great Lakes basin. Due to time and resource constraints, Grass Carp and Black Carp were not
be included in this targeted risk assessment. A binational risk assessment, following a similar
process for the bigheaded carps, could be conducted for Grass and Black carps focusing on the
Great Lakes.
45
a
100
Very
likely
Probability of Introduction
M, H, E
O
S
Very
unlikely 0
0
100
b
100
Very
likely
Probability of Introduction
M, H, E
Very
unlikely
O
S
0
0
100
Negligible
Extreme
Magnitude of Ecological Consequence
Figure 13. Probability of introduction and magnitude of the ecological consequences over a) 20 years and
b) 50 years as a graphic representation to communicate risk. S=Lake Superior, M=Lake Michigan,
H=Lake Huron, E=Lake Erie, O=Lake Ontario; ellipses are representative of amount of certainty around
rank.
46
Aquatic invasions can be considered natural disasters (Ricciardi et al. 2011). The further into
the invasion process (pre-arrival, arrival, survival, establishment, or spread), the more difficult
and costly it is to halt or manage (Leung et al. 2002). Preventing arrival is therefore the most
feasible and effective management effort that can be taken (Mack et al. 2000, Leung et al.
2002). As time passes, bigheaded carps continue moving toward the Great Lakes and the time
to prevent their arrival shrinks. Therefore, activities that specifically target pre-arrival, such as
some of those being implemented by the Asian Carp Regional Coordinating Committee in the
United States, continue to be important (see ARCC 2011 and ARCC-MRRWG 2011 for
complete descriptions). Likewise, given that the number of individuals entering an ecosystem
(i.e., propagule pressure) is paramount to establishment (Lockwood et al. 2005) and that prompt
removal of initial individuals detected from a system is key to effective control (Simberloff 2010),
additional actions targeting arrival, survival, establishment, and spread provide additional
opportunities to interrupt the invasion process (on-going efforts in the US described in ARCC
2011 and ARCC-MRRWG 2011).
There is an expected time lag associated with seeing the full consequences of an established
population of bigheaded carps in the Great Lakes, however, this should not be interpreted that
there is time to wait before acting. The opportunity to prevent these predicted consequences
may not persist. Management options exist and are ongoing in the United States, and further
research can be conducted, to interrupt the trajectory to minimize the risk predicted within this
assessment. We can, with effective prevention and control actions, continue to delay when
these consequences would occur if bigheaded carps became established in the Great Lakes.
This delay will provide time to conduct further research into eradication and control options, as
well as minimize and postpone overall costs of high control and management efforts, and costs
associated with impacts.
6.0 TARGETTED MANAGEMENT QUESTIONS
At three workshops (November 2010, May 2011, and June 2011) held for managers and
decision-makers around the Great Lakes from both sides of the border, specific management
questions were compiled. These questions represent the key information needs by managers
and decision-makers to be supported from this risk assessment. The summary of advice to
these questions stemming from this risk assessment is presented in Table 14 and was not
developed by the authors for review, but rather by consensus at the peer review meeting.
47
Table 14. Summary of advice to management questions presented by Great Lakes managers and
decisions makers and location within the risk assessment where the advice can be found.
Management Question
How risky are the
various points of arrival?
How effective is the
barrier?
Are the Great Lakes too
cold?
Are the right
environmental
conditions available?
Is there enough food
and where?
What number of
individuals is needed to
establish a population?
What is the potential
biomass?
Where will they be most
abundant?
What characteristics
make for suitable
spawning tributaries?
What/how many
tributaries would support
spawning and
recruitment?
Could they spawn
directly in the Great
Lakes?
What is the timeframe
and direction of spread?
How long before they
Summary of Answer
In general, the physical connections represent higher likelihood
than human-mediated releases; however, there is much lower
certainty associated with the ranks of human-mediated releases.
The highest likelihood of arrival into the basin is from the CAWS
into Lake Michigan.
A detailed evaluation of the effectiveness of the electric dispersal
barrier was not conducted in this risk assessment.
No.
Yes.
Yes. There is enough food, especially in Green Bay, Saginaw Bay,
Lake St. Clair, and Lake Erie. Warm embayments in lakes Superior
and Ontario should also provide suitable amounts of food.
Modeling suggests that under ideal conditions (assuming fish locate
suitable rivers, a low spawning failure rate, and that sexual maturity
is reached at 3 years of age), as few as 10 mature females and 10
mature males in the basin of a single Great Lake have a greater
than 50% chance of successfully spawning (Currie et al. 2011).
Bigheaded carps have the potential to become a dominant biomass
in favourable locations.
Lake Erie, including Lake St. Clair, and high productivity
embayments of lakes Superior, Michigan, Huron and Ontario.
Some general knowledge exists on the characteristics of suitable
spawning tributaries; however, specific characteristics are identified
as a critical knowledge gap within this risk assessment.
Suitable spawning tributaries are found in all lakes.
United States: 21 suitable spawning tributaries in the American
Great Lakes basin are unimpounded from mouth to at least 100km
upstream. More detailed analyses of tributary characteristics for
Lake Erie suggest that 3 out of 8 tributaries examined could provide
suitable spawning habitat and that 4 others appeared moderately
suitable (Kocovsky et al. 2012).
Canada: 41 suitable spawning rivers in the Canadian Great Lakes
basin are unimpounded from mouth to at least 100km upstream.
More detailed analyses of tributary characteristics suggest that
suitable spawning conditions exist in at least 49 Canadian Great
Lake tributaries (Mandrak et al. 2011).
This is identified as a critical knowledge gap within the risk
assessment. See the proceedings document from the peer review
meeting (DFO 2012a) for a list of prioritized (by consensus of the
peer review participants) knowledge gaps.
Varies depending on arrival point within the basin, but predicted to
be less than 10 years with direction likely Michigan to Huron to Erie.
Less than 5 years after arrival into the connected Great Lakes
48
reach Canadian waters?
What level of population
would be an acceptable
level of risk/impact?
What are the impacts to
recruitment – food,
behavioural disruption?
Will a fishery be lost?
Loss of diversity,
richness or production?
Is there a variation of
impacts with variation in
abundance levels of
bigheaded carps?
Will there be a
cumulative impact of two
more planktivorous
invaders?
Need links of ecological
impacts to use for socioeconomic uses and
activities
What is the timeframe of
risk for each element?
What are the
confounding issues?
Where are the most
vulnerable areas?
Help inform rapid
response?
What are some
mitigation options?
basin via Lake Michigan.
This is outside the scope of this risk assessment.
Recruitment of fishes with pelagic early life stages are expected to
decline. Mechanisms are unclear.
Fish community responses would be variable and difficult to predict.
Accordingly, impact on fisheries are difficult to predict and outside
the scope of this risk assessment.
Yes. Higher abundance of bigheaded carps would lead to greater
ecological consequences.
Different changes in plankton communities are predicted than have
been seen with planktivores that have previously invaded the Great
Lakes. Cumulative impacts are difficult to predict.
Select qualitative consequences have been identified; some
specific quantitative information could not be completed within this
risk assessment timeframe.
Beyond current efforts underway, if no additional management
actions around the entire basin are taken:
 Arrival – impending;
 Survival – immediate upon arrival;
 Establishment – 5 to 20 years (short in southern basin, longer in
Lake Superior);
 Spread – 5 to 20 years; and,
 Consequences – will build over time.
Question is too broad to provide meaningful advice.
Lake Erie, including Lake St. Clair, and high productivity
embayments of lakes Superior, Michigan, Huron (including the
Huron-Erie corridor), and Ontario. Overlap of identified spawning
tributaries and potential points of arrival.
See above points of arrival, abundant areas, spawning tributaries,
and vulnerable areas.
A discussion of mitigation options is outside the scope of this risk
assessment; however, potential entry routes have been identified to
inform prevention activities.
49
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