Ministry of Natural Resources
Double-crested cormorants: Their distribution and potential impact on fisheries in northwestern Ontario Scott Parker Double-crested cormorants (Phalocrocorax auritus, henceforth cormorants) are large, fish-eating birds found on numerous waterbodies throughout Ontario 1. The cormorant has undergone dramatic fluctuations in population and range expansion throughout the past century. Most significant is the population explosion and re-invasion of the Great Lakes region and surrounding waterbodies since the mid 1970s 1,2. Their consumption of fish as prey as well as their impact on the environment has resulted in widespread public concern. Many anglers, tourist outfitters, and commercial fishers are concerned that cormorants deplete fish populations through predation, or that they remove a disproportionate amount of prey biomass that supports game fish populations, such as walleye (Sander vitreus). Similar concerns have been raised regarding the increasing movement and establishment of breeding colonies of cormorants on inland waterbodies in northwestern Ontario. As such, cormorant management has become a contentious issue among stakeholders and resource users in the region. Cormorants are found across Canada, from the Pacific coast to the Atlantic Ocean, and from as far north as James Bay and south throughout the Great Lakes 3. Cormorants were known to be present in northwestern Ontario on Lake of the Woods as early as the 1700s. It is believed that cormorants first colonized the Great Lakes region early in the 20th century with the first reports of nesting birds in 1913 at the western end of Lake Superior 2,4. Cormorant numbers in the Great Lakes region increased steadily until the 1950s. During the 1960s and 1970s cormorant populations experienced devastating declines and were almost extirpated as a result of toxic contaminants, specifically the pesticide DDT (dichlorodiphenyltrichloroethane). Cormorants were especially susceptible to the biomagnification of DDT that, when metabolized, produced DDE (dichlorodiphenyltrichloroethylene). The high level of contamination was related to eggshell thinning, hatching deformities, and extensive reproductive failure throughout the Great Lakes region and elsewhere 3. By 1973, the entire Great Lakes population declined to approximately 130 breeding pairs and were extirpated completely from Lake Superior 3,5. Since then, populations in the Great Lakes region have increased dramatically over the past three decades.
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Cormorants are migratory and are present in the Great Lakes region from approximately mid-April until September 3,5. They generally do not reach more northerly latitudes (e.g. Canadian prairies) until lateApril or early May 6. Dense colonies nest in trees or on the ground on islands and peninsulas in close proximity to feeding areas. Cormorants typically forage during the day in shallow water that is less than 10 m deep and within 5 km of shore. Foraging is usually solitary, but they have been observed fishing in large cooperative flocks 6. There has been extensive research on the diet of cormorants in North America 6,7,8,9,10,11. Cormorants typically feed on slow-moving or schooling fish that are approximately 15 cm in length or smaller 7,9,12,13. They are a generalist feeder preying on the most abundant or readily available fish species present 9. The majority of studies have shown that cormorants feed primarily on species of little to no commercial value such as alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax), gizzard shad (Dorsoma cepadianum), and various Cyprinid (minnow) species 5,6,9,10,11,14. However, cormorants will feed on sport fish such as yellow perch (Perca flavescens), walleye (Sander vitreus), and smallmouth bass (Micropterus dolomieu), where available 15,16,17,18,19. There is an abundance of contradictory evidence regarding the impact of cormorants on recreational fisheries. Some research suggests that cormorants may have been a factor in the localized decline or suppression of recreational fisheries 15,16,17,18,19,20. Other research indicates that cormorant predation is not a significant contribution to the overall mortality of fish populations 10,21,22,23,24,25. Declines in yellow perch and smallmouth bass stocks in the eastern basin of Lake Ontario been attributed to increasing cormorant numbers 15,17. Similar declines in yellow perch abundance in northern Lake Huron, coincided with increasing cormorant numbers 16. However, in both instances, other factors such as overfishing likely contributed to fishery declines 16. Other studies acknowledge the extent of cormorant predation but fail to relate cormorants to recreational fishery declines. In the Les Cheneaux Islands of Lake Huron, cormorant consumption of yellow perch had little effect on its population size or the recreational
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harvest 23. Cormorants did not influence yellow perch density or negatively impact population size in Dore Lake, Saskatchewan 21, despite heavy predation on fish less than 10 cm in length. Similar conclusions from an extensive review 10 state that cormorants had little impact on sport fish populations, but recognized that there may be localized situations where cormorants could have an impact, such as on congregations of small fish in nearshore spawning areas 10.
fish diversity. However, estimates of prey consumption can be calculated using published formulas 23,25,27,28,29,30. As a general rule, adult cormorants consume 20 to 25% of their body weight per day 3,27. In a recent review 29, cormorant consumption ranged from 17.9 to 27.7% of adult body weight 29. Assuming an adult body weight of 2,000 g 29 (4.4 lb.), an adult cormorant would consume an average of 350 to 550 g of fish per day. Since 2008, 305 lakes in fisheries management zones (FMZ) 4, 5, and 6 in northwestern Ontario have been studied as part of Ministry of Natural Resources’ (MNR) broad-scale fisheries monitoring program. In addition to fisheries specific data, other important information for fisheries management is being collected, such as the presence of nesting or foraging cormorants. Cormorants were observed on 36 of the 305 lakes in the Northwest Region (Figure 1), however, no nesting or breeding cormorants were observed. Cormorants were almost always observed on inland lakes near large waterbodies such as Lake Nipigon, Lake of the Woods, and Rainy Lake. These large waterbodies generally support nesting colonies of cormorants and likely act as the source population for foraging individuals or small flocks of birds on nearby smaller lakes and rivers. The broadscale monitoring program may serve as a useful method
In most studies, the number of sport fish (yellow perch, walleye, etc.) consumed by cormorants amounts to only a fraction of each species overall total mortality and is generally only a small percentage of what other fish-eating birds, predators, and anglers take from the population. For instance, in the eastern basin of Lake Ontario where the cormorant population number in the tens-of-thousands, of the estimated 418 million kg of forage fish available, only 0.5% was consumed by cormorants, whereas, salmonines (salmon, lake trout) consumed 13.4% 3. In another study, the diet composition of cormorants in Lake Superior’s Black Bay and Thunder Bay consisted primarily of stickleback (Gasterosteidae), rainbow smelt, Cyprinid spp. (minnows), and troutperch (Percopsis omiscomaycus) 5. Yellow perch and walleye accounted for 7.9% and 1.6% of their diet respectively, of which the majority were consumed at one location during the spring spawning period 5. In Lake Erie, migrant common and red-breasted mergansers consumed the greatest percentage of fish (41%) of all waterbirds, including cormorants 26. In the same study, yellow perch and walleye comprised a significantly higher percentage in the diet of mergansers, great blue herons, terns, and gulls than in cormorants 26.
The majority of cormorant feeding and diet composition research has been conducted near large cormorant breeding rookeries on extremely large waterbodies (Great Lakes), with diverse fish communities. These waterbodies support vast populations of invasive forage fish such as alewife, rainbow smelt, round goby (Neogobius melanostomus) Cormorant Observations and stickleback that comprised the majority of the cormorant diet. There is little information on the impact Figure 1. Red markers indicate the location of waterbodies where cormorant(s) of cormorant predation on relatively were observed in northwestern Ontario during the broad-scale monitoring small boreal lakes with limited prey program between 2008–2010.
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for monitoring the regional distribution of cormorants on waterbodies in northwestern Ontario over time. Cormorant numbers have expanded rapidly over the past several decades throughout much of the Great Lakes. Colonies are also found on a few large inland lakes in northwestern Ontario but are not widespread on smaller lakes in the region. Several studies show that predation from a few cormorants on a single waterbody does not pose a significant threat to sport fish populations and small numbers of cormorants have a similar impact on a fishery as other fish-eating waterbirds such as loons, great-blue herons, or mergansers 26,31. However, the relatively recent re-invasion of cormorants in the northwest region and the unknown potential impact on northern boreal fisheries warrants continued monitoring.
Acknowledgements Numerous individuals contributed to the development of this report. Foremost, I would like to thank Kim Armstrong for providing his guidance, insight, and review. I would also like to thank Darryl McLeod who provided comments and information on cormorants in FMZ 5, Tom Mosindy for reviewing this report, Dan Lix for creating maps showing cormorant observations, and the broad-scale fisheries monitoring program for data collected. Finally, many thanks go to Jessica Gagnon and Annalee McColm for desktop publishing.
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Literature cited 1. Weseloh, D.V.C., C. Pekarik, T. Havelka, G. Barrett, and J. Reid. 2002. Population trends and colony locations of double-crested cormorants in the Canadian Great Lakes and immediately adjacent areas, 1990–2000: A manager’s guide. Journal of Great Lakes Research 28(2): 125–144. 2. Weseloh, D.V., P.J. Ewins, J. Struger, P. Mineau, C.A. Bishop, S. Postupalsky, and J.P. Ludwig. 1995. Double-crested cormorants of the Great Lakes: Changes in population size, breeding distribution and reproductive output between 1913 and 1991. Colonial Waterbirds 18: 48–59. 3. Weseloh, D.V., and B. Collier. 1995. The rise of the double-crested cormorant on the Great Lakes: Winning the war against contaminants. Great Lakes Fact Sheet, No. EN 40–222/2–1995 E. Weseloh and Collier, Ontario Region, 12 pp. 4. Baillie, J.L. 1947. The double crested cormorant in Ontario. Canadian Field Naturalist 61(4): 199–126. 5. Ratcliff, B. 2004. Breeding history and diet composition of double-crested cormorant (Phalacrocorax auritus) Colonies on Black Bay and Thunder Bay, Lake Superior in 2003. Upper Great Lakes Management Unit–Lake Superior. Ontario Ministry of Natural Resources. Thunder Bay, ON. 11 pp. 6. Wires, L.R., F.J. Cuthbert, D.R. Trexel and A.R. Joshi. 2001. Status of the double-crested cormorant (Phalacrocorax auritus) in North America. Final Report to USFWS. 359 pp. 7. Neuman, J., D.L. Pearl, P.J. Ewins, R. Black, D.V. Weseloh, M. Pike, and K. Karwoski. 1997. Spatial and temporal variation in the diet of double-crested cormorants (Phalacrocorax auritus) breeding on the lower Great Lakes in the early 1990s. Canadian Journal of Fisheries and Aquatic Sciences 54: 1569– 1584. 8. Glahn, J.F., J.B. Harrel, and C. Vyles. 1998. The diet of wintering double-crested cormorants feeding at lakes in the southeastern United States. Colonial Waterbirds 21: 446–452. 9. Bur, M.T., Tinnirello, S.L., Lovell, C.D., and Tyson, J.T. 1999. Diet of the double-crested cormorant in western Lake Erie. Symposium on double-crested cormorants: Population status and management issues in the Midwest (Dec. 9, 1997, Milwaukee, WI) USDA APHIS Technical Bulletin No. 1879. USDA, Animal and Plant Health Inspection Service. Washington, D.C.
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10. Trapp, J.L., S.J. Lewis, and D.M. Pence. 1999. Double-crested cormorant impacts on sport fish: Literature review, agency survey, and strategies. Symposium on double-crested cormorants: Population status and management issues in the Midwest (Dec. 9, 1997, Milwaukee, WI) USDA APHIS Technical Bulletin No. 1879. USDA, Animal and Plant Health Inspection Service. Washington, D.C. 11. Johnson, J.H., R.M. Ross, and R.D. McCullough. 2002. Little Galloo Island, Lake Ontario: A review of nine years of double-crested cormorant diet and fish consumption information. Journal of Great Lakes Research. 28(2): 182–192. 12. Craven, S.R., and E. Lev. 1987. Double-crested cormorant in the Apostle Islands, Wisconsin, USA: Population trends, food habits, and fishery depredation. Colonial Waterbirds 10: 64–71. 13. Weseloh, D.V., and P.J. Ewins. 1994. Characteristics of a rapidly increasing colony of double-crested cormorants (Phalacrocorax auritus) in Lake Ontario: Population size, reproductive parameters and band recoveries. Journal of Great Lakes Research 20: 443–456. 14. Johnson, J.H., R.M. Ross, and C.M. Adams. 1999. Diet composition and fish consumption of doublecrested cormorants in eastern Lake Ontario, 1998. New York State Department of Environmental Conservation Special Report–February 1, 1999. 15. Burnett, J.A.D., N.H. Ringler, B.F. Lantry, and J.H. Johnson. 2002. Double-crested cormorant predation on yellow perch in the eastern basin of Lake Ontario. Journal of Great Lakes Research 28(2): 202–211. 16. Fielder, D.G. 2008. Examination of factors contributing to the decline of the yellow perch population and fishery in Les Cheneaux Islands, Lake Huron with emphasis on the role of doublecrested cormorants. Journal of Great Lakes Research 34: 506–523. 17. Lantry, B.F., T.H. Eckert, C.P. Schneider, and J.R. Chrisman. 2002. The relationship between smallmouth bass and double-crested cormorants in the eastern basin of Lake Ontario. Journal of Great Lakes Research 28: 193–201. 18. Rudstam, L.G., A.J. VanDeValk, C.M. Adams, J.T.H. Coleman, J.L. Forney, and M.E. Richman. 2004. Cormorant predation and the population dynamics of walleye and yellow perch in Oneida Lake. Ecological Applications 14: 149–163.
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19. VanDevalk, A.J, C.M. Adams, L.G. Rudstam, J.L. Forney, T.E. Brooking, M.A. Gerken, B.P. Young, and J.T. Hooper. 2002. Comparison of angler and cormorant harvest of walleye and yellow perch in Oneida Lake, New York. Transactions of the American Fisheries Society 131: 27–39. 20. Fielder, D. G. 2010. Response of yellow perch in Les Cheneaux Islands, Lake Huron to declining numbers of double-crested cormorants stemming from control activities. Journal of Great Lakes Research 36: 207– 214. 21. Barks, P.M., J.L. Doucette, and C.M. Somers. 2010. Lack of angling-sized yellow perch in a Canadian boreal lake: Potential influences of growth rate, diet, and predation by double-crested cormorants. Transaction of the American Fisheries Society 139: 1029–1040 22. Diana, J.S., G.Y. Belyea, and R.D. Clark, Jr. eds. 1997. History, status and trends in populations of yellow perch and double-crested cormorants in Les Cheneaux Islands, Michigan. State of Michigan Department of Natural Resources, No. 17. Ann Arbor. 23. Diana, J.S., S. Maruca, and B. Lowe. 2006. Do increasing cormorant populations threaten sport fishes in the Great Lakes? A case study in Lake Huron. Journal of Great Lakes Research 32: 306– 320. 24. Korfanty, C., W.G. Miyasaki, and J.L. Harcus. 1999. Review of the population status and management of double-crested cormorants in Ontario. Symposium on double-crested cormorants: Population status and management issues in the Midwest (Dec. 9, 1997, Milwaukee, WI) USDA APHIS Technical Bulletin No. 1879. USDA, Animal and Plant Health Inspection Service. Washington, D.C. 25. Dalton, C.M, D. Ellis, and D.M Post. 2009. The impact of double-crested cormorant (Phalacrocoax auritus) predation on anadromous alewife (Alosa pseudoharengus) in south-central Connecticut, USA. Canadian Journal of Fisheries and Aquatic Sciences 66: 177–186. 26. Hebert, C.E., and H.A. Morrison. 2003. Consumption of fish and other prey by Lake Erie waterbirds. Journal of Great Lakes Research 29: 213–227. 27. Hatch, J.J., and D.V. Weseloh. 1999. Double-crested cormorant (Phalacrocorax auritus). In: A. Poole and F. Gill (eds.). The Birds of North America, No. 441. The Birds of North America Inc., Philadelphia, PA.
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28. Derby, C.E. and J.R. Lovvorn. 1997. Predation on fish by cormorants and pelicans in a cold water river: A field modeling study. Canadian Journal of Fisheries and Aquatic Sciences 54: 1480–1493. 29. Ridgway, M.S. 2010. A review of estimates of daily energy expenditure and food intake in cormorants (Phalacrocorax spp.). Journal of Great Lakes Research 36: 93–99. 30. Seefelt, N.E., and J.C. Gillingham. 2008. Bioenergetics and prey consumption of breeding double-crested cormorants in the Beaver Archipelago, northern Lake Michigan. Journal of Great Lakes Research 34: 122–133. 31. McIntyre, J.W., and J.F. Barr. 1997. Common loon (Gavia immer). In The Birds of North America, No. 313 (A. Poole and F. Gill, Eds.). Academy of Natural Sciences, Philadelphia, and American Ornithologists’ Union, Washington, D.C.
Parker, S. 2011. Double-crested cormorants: Their distribution and potential impact on fisheries in northwestern Ontario. Ont. Min. Natur. Resour., Northwest Sci. & Info, NWSI Aquatic Update 20115. 5 pp. © 2011, Queen’s Printer for Ontario 62732 ISBN 978-1-4435-7097-8 (PDF)
Northwest Science and Information Science and Information Branch Ontario Ministry of Natural Resources 173 25th Sideroad Rosslyn [Thunder Bay], Ontario P7K 0B9 Tel: 807 939–2501 Website: ontario.ca/nwsi Cette publication spécialisée n’est disponible qu’en anglais