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Eisenhower, Marc David

Wildlife and Fisheries Biology Program

2008

M.S.

We studied the interactions of Double-crested Cormorants (Phalacrocorax auritus) and fish in a constricted shallow basin near a cormorant nesting site (Young Island) in Lake Champlain, Vermont. Much of the basin was dominated by submerged aquatic vegetation (SAV), which led us to investigate how fish residing among SAV could affect cormorant foraging. We collected data on foraging flocks, individual birds and their stomach contents, the fish community, and SAV from May to September. Fish were most abundant in August and September; they did not migrate from the basin during times of high water temperature, low dissolved oxygen (DO), or the greatest densities of SAV. Although many fish species (N=28) were collected, yellow perch (Perca Jlavescens) comprised almost half of the fish community and were the major prey in cormorant stomachs. Double-crested Cormorants regularly foraged in the basin until early August when they began foraging in more distant areas. This shift occurred soon after the peak in SAV biomass and height, which covered essentially the entire area frequented previously by foraging birds. The lag time between the occurrence of peak SAV growth and the birds foraging in other locations is predictable based on the benefit:cost relation of foraging models.