Harvey, C. J.. University of Wisconsin-Madison, cjharvey@students.wisc.edu
Kitchell, J. J.. University of Wisconsin-Madison, kitchell@macc.wisc.edu

The offshore food web of western Lake Superior was examined by analysis of the stable isotopes of nitrogen (15-N) and carbon (13-C). Samples from across the region imply a food web with a high degree of omnivory. Siscowet lake trout were the top predator and appeared to move from their hypolimnetic habitat to feed on prey in shallower waters. Exotic Pacific salmon were trophically distinct from native predators. In general, western Lake Superior's food web was dilute in 15-N relative to that of Lake Ontario, possibly as a result of lower human population in the Lake Superior drainage basin. Isotopic values of many species varied spatially. We tested for a potential point source of 15-N in western Lake Superior by sampling along a distance gradient beginning at the cities of Duluth and Superior. Only one species, slimy sculpins, exhibited strong enrichment of 15-N. Between-site differences in 15-N of select taxa demonstrated that rainbow smelt were the most mobile fish; their 15-N had low variance and indicated an integration of prey resources across a broad geographic region.
Day: Wednesday, Feb. 3
Time: 11:30 - 11:45am
Location: Eldorado Hotel
Code: SS32WE1130E