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Monday, January 29 • 2:00pm - 2:20pm
SALMONIDS: Shifts in Lake Trout (Salvelinus namaycush) Diets in Lake Michigan: An Annual and 5-year Assessment

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AUTHORS. Miles Luo, University of Michigan, School for Environment & Sustainability; Charles Madenjian, US Geological Survey, Great Lakes Science Center; Jim Diana, University of Michigan, School for Environment & Sustainability; Matthew Kornis, U.S. Fish & Wildlife Service, Green Bay Fish and Wildlife Conservation Office; Charles Bronte, U.S. Fish & Wildlife Service, Green Bay Fish and Wildlife Conservation Office

ABSTRACT.                 Recent surveys have shown that prey fish communities in Lake Michigan have been steadily changing, highlighted by declines in both the quantity and quality of Alewife (Alosa pseudoharengus). Although current food web models exist for both lakes, it has been unclear how the declining abundance of Alewife has affected the diets of predatory salmonids, such as Lake Trout (Salvelinus namaycush). Previous studies have shown that Lake Trout are heavily reliant on Alewife as a prey species in the northeastern of Lake Michigan. To evaluate shifts in diet composition of Lake Trout, we analyzed stomach contents of individual Lake Trout caught north and east of Frankfort, MI during gillnet surveys and fishing tournaments from May through October of 2016. We then compared the composition of 2016 diets to those found in the most recent similar survey conducted in 2011. We also sought to create a diet schedule to summarize changes in Lake Trout feeding patterns throughout the year. Overall, we found that Lake Trout diets mainly consisted of Alewife and Round Goby (Neogobius melanstomus). By weight, Round Goby percentages in Lake Trout diets greatly increased from 2011 to 2016. However, this diet shift was only seen May and June, while diets were still mainly comprised of Alewife in later months. Further statistical analyses showed that the gear type and survey location were far less important than the collection month in predicting diet composition. Although Lake Trout show some flexibility in the prey consumed in spring months, Alewife still appears to be the most important component of their diet. This continued reliance on declining Alewife populations has the potential to significantly alter the Lake Michigan food web and impact the viability of regional salmonid stocking programs. 

Monday January 29, 2018 2:00pm - 2:20pm CST