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**The title, authors, and abstract for this completion report are provided below. For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209** Comparative Modelling of the Ecosystem Impacts of Exotic Invertebrates and Productivity Changes on Fisheries in the Bay of Quinte and Oneida Lake Marten A. Koops2, Brian J. Irwin3, Jennifer E. MacNeil4, E. Scott Millard5 and Edward L. Mills6
2 Great Lakes Laboratory for Fisheries and Aquatic Sciences Fisheries and Oceans Canada 867 Lakeshore Road Burlington, ON, L7R 4A6 Canada p: 905-336-4559 f: 905-336-64327 e: KoopsM@dfo-mpo.gc.ca 3 Cornell Biological Field Station Cornell University 900 Shackelton Point Road Bridgeport, NY, 13030 USA p: 315-633-9243 f: 315-633-2358 e: bji4@cornell.edu 4 Department of Biology University of Waterloo 200 University Avenue West Waterloo, ON, N2L 3G1 Canada p: 519-888-4567 f: 519-746-0614 e: jmacneil@rbg.ca 5 Great Lakes Laboratory for Fisheries and Aquatic Sciences Fisheries and Oceans Canada 867 Lakeshore Road Burlington, ON, L7R 4A6 Canada p: 905-336-4702 f: 905-336-64327 e: MillardS@dfo-mpo.gc.ca 6 Cornell Biological Field Station Cornell University 900 Shackelton Point Road Bridgeport, NY, 13030 USA p: 315-633-9243 f: 315-633-2358 e: elm5@cornell.edu Abstract: The Great Lakes ecosystems have been perturbed by a number of stressors, such as changing nutrient loadings, changes in exploitation pressures, and increasing abundances of non-native species. Over the past 30 years, both the Bay of Quinte (Lake Ontario) and Oneida Lake (New York) have experienced similar ecosystem changes going through increased phosphorus loadings leading to eutrophication, followed by phosphorus control and reduced phosphorus concentrations, increased water clarity, increased benthification and macrophyte abundance, invasion by exotic species (particularly zebra mussels, Dreissena polymorpha), the arrival and increased abundance of double-crested cormorants (Phalacrocorax auritus), and declining walleye (Sander vitreus) stocks. The Bay of Quinte and Oneida Lake are particularly attractive ecosystems within which to study these impacts due to the wealth of data on their food webs. Three time periods were identified from long-term data for each ecosystem (prephosphorus control, post-phosphorus control, and post-zebra mussel invasion). Three approaches were used to investigate the combined effects of oligotrophication, benthification and exotic invaders on key fishes in the Bay of Quinte and Oneida Lake, with special attention paid to walleye and yellow perch (Perca flavescens). The three approaches were (i) comparative ecosystem modelling using Ecopath with Ecosim, (ii) age-based estimation modelling of walleye and path analysis of yellow perch growth focusing on Oneida Lake, and (iii) stable isotope analyses to elucidate the feeding relationships in key fishes of the Bay of Quinte and Oneida Lake. Each of these approaches provided unique pieces of information about the ecosystems and how they changed. Where there is overlap the conclusions are consistent across approaches. Productivity changes and exotic invertebrates together have led to ecosystems that are more benthic, though the Bay of Quinte less so than Oneida Lake. Diets of fishes such as walleye and yellow perch have changed, particularly in Oneida Lake where yellow perch diets have shifted away from direct overlap and competition with zebra mussels. From the population specific modelling applied to Oneida Lake, it is apparent that ecosystem changes have affected the growth and mortality of yellow perch and the mortality of sub-adult walleye. While many of the impacts on these two ecosystems have been similar, the Ecosim results examining potential explanations for the decline of walleye differed. In the Bay of Quinte, Ecosim results suggest that a combination of increased fishing pressure and food web impacts from the invasion of zebra mussels played a role in the decline of walleye, whereas Ecosim results for Oneida Lake suggest that a combination of trophic impacts from zebra mussel invasion and increased predation from cormorants played a role in the decline of walleye in Oneida Lake. |