Size selective predation on Mysis diluviana in pelagic and benthic habitats of Lake Champlain

Mysis diluviana, a freshwater macroinvertebrate, plays a pivotal role in the food web ecology of Lake Champlain. Mysis serve as a primary food source for a variety of forage fish species in both benthic and pelagic habitats. These include Alewife (Alosa pseudoharengus), Rainbow smelt (Osmerus mordax), Lake trout (Salvelinus namaycush), and Slimy sculpin (Cottus cognatus). Understanding Mysis diluviana population dynamics is important in informing the maintenance of fish populations, and other fisheries management and restoration projects. Mysis populations have been measured using pelagic sampling techniques at night, due to extensive diel vertical migration, however recent studies indicate that Mysis exhibit partial diel vertical migration, in which a portion of the population remains benthic at night. This renders the resulting estimates from these population sampling methods incomplete. Additionally, sampling pelagic and benthic communities at night has shown differences in Mysis size distribution between the two habitats. Studies have indicated that Mysis sampled from pelagic habitat are consistently smaller than those sampled from benthic habitat. We hypothesize that the pelagic predator fish are selecting larger Mysis than benthic predator fish, skewing the average animal sizes in the two habitats. The purpose of this study was to test the size selective predation hypothesis by analyzing the diets of both benthic and pelagic fish that prey on Mysis. Lengths of fish from both habitats in Lake Champlain were analyzed compared to lengths of Mysis found in their stomachs. Mysis and fish were concurrently sampled from both habitats. Mysis were measured and counted for a size distribution estimate, to be compared with Mysis from the stomach dissections