Foodweb dysfunction is one of the leading theories as to why lake trout are not successfully spawning in Lake Michigan.  At last count more than 180 exotic species now reside in the Great Lakes and their presence has irreversibly changed fish diets.  Lake trout historically consumed native chubs, sticklebacks and sculpins but now much of their diet consists of exotic alewives, gobies and smelt.  These changes, most notably the addition of alewives, have been linked with high egg mortalities in lake trout.  In an effort to further understand how foodweb dysfunction may limit reproductive success, Dale Hanson, biologist at the Green Bay National Fish and Wildlife Conservation Office, has teamed up with researchers from SUNY-Brockport and the Illinois Natural History Survey (ILNHS) to determine what lake trout and yellow perch feed on in the lake and how a fish's diet choices may relate to their reproductive success.  This work, funded  by the Great Lakes Fishery Trust, began this spring and will be completed in 2010.

In May, 2008 the Service collected lake trout, yellow perch, forage fish, invertebrates and zooplankton from Lake Michigan near Algoma, Wis. while the ILNHS obtained similar samples from the lake near Waukegan, Ill.  These "foodweb" samples will be analyzed at SUNY to determine the biological make-up of their fats, also referred to as lipids.  The lipids, which are found in all animals, contain various fatty acids and some of these are useful markers because they vary in size and create a fatty acid "signature" that is often unique among animals at the base of the foodweb.  These fatty acids move through the food web from prey to predator and therefore the animal diets can be reconstructed by comparing the fatty acid "signatures" among animals in the foodweb.  Additional supporting studies will be performed in the laboratory to relate lake trout and yellow perch egg survival rates with a specific diet.  

Ultimately, this research may enable biologists a practical, cost-effective method to determine the foodweb dynamics for specific regions within Lake Michigan and make inferences regarding egg survival based on the available prey base.