Midwest Fish & Wildlife Conference 2019

AUTHORS: Dan Traynor, Shawn Sitar – Michigan Department of Natural Resources Marquette Fisheries Research Station; Ji He, Michigan Department of Natural Resources Alpena Fisheries Research Station

ABSTRACT: Lake trout are the dominant piscivore in the upper Great Lakes and are a major focus in fisheries management.  Lake populations underwent catastrophic collapses in the middle of the 20th century but have recovered in Lake Superior due to diligent management actions.  Recently, lake trout recovery has improved in Lake Huron and there are indications that Lake Michigan may be following suit.  Although controls on fishing, sea lamprey suppression, and stocking of hatchery fish were instrumental in lake trout recovery, we pose that dietary flexibility also contributed to its success.  We analyzed the diet of a broad size range of lean and siscowet lake trout from spring and summer gill net surveys conducted in southern Lake Superior and western Lake Huron during 2005-2016.  In addition to categorizing prey items by taxa, we grouped prey items by habitat types to further describe dietary flexibility.  We found that lake trout diet compositions were diverse in both lakes Superior and Huron. Generally, the diet of leans and siscowets in Lake Superior were similar.  We observed ontogenetic diet shifts in both lean and siscowet lake trout with small fish feeding predominantly in the benthos expanding to the pelagic zone as fish grew larger.  Progress in lake trout recovery in Lake Huron coincides with collapses in alewife abundance and declines in Chinook Salmon populations.  We pose that lake trout success in rapidly changing ecosystems is partly due to its high dietary flexibility and declines in Great Lakes Chinook salmon are due to its strong reliance on pelagic prey such as alewife.