EVIDENCE FOR YELLOW PERCH PREDATION ON BYTHOTREPHES-CEDERSTROEMI IN SOUTHERN LAKE-MICHIGAN

Zooplankton and yellow perch (Perca flavescens) were collected on 7 August 1990 in Lake Michigan at sites near Michigan City, Indiana, to determine abundance of Bythotrephes cederstroemi and to attempt to document possible predation by yellow perch. Zooplankton analysis revealed the concentration of Bythotrephes was highest in shallow near-shore water at 5 m (15/m3) but dropped sharply at 10 m (2/m3) and 15 m (1/m3) sample sites. Stomach analyses of 48 yellow perch ranging in length from 80 to 179 mm revealed four fish had empty stomachs, four had nearly empty stomachs, 17 had half-full stomachs, and 23 had full stomachs. Bythotrephes was the dominant prey item, occurring in 95% of the stomachs which contained food. Numbers of Bythotrephes ranged from 0-323 per stomach with a mean of 48 (SD = 59). Diptera larvae and pupae were also important food items during this time occurring in 77% of the stomachs containing food. Diptera and other zooplankton were relatively more important than Bythotrephes to yellow perch < 100 mm maximum total length but Bythotrephes was eaten by all of the fish greater-than-or-equal-to 100 mm and tended to be the major food item consumed by the larger fish. These data reveal Bythotrephes is an easily captured food source for yellow perch in extreme southern Lake Michigan.