EVALUATION OF COMPETITION BETWEEN AGE-0 YELLOW PERCH (PERCA-FLAVESCENS) AND GIZZARD SHAD (DOROSOMA-CEPEDIANUM) IN ONEIDA LAKE, NEW-YORK

Diet and growth of age-0 yellow perch (Perca flavescens) and age-0 giz zard shad (Dorosoma cepedianum) were compared during June-August 1990 and 1991. In both years, Daphnia dominated the zooplankton community i n June and early July but disappeared in mid-July and early August. Ag e-0 yellow perch consumed primarily Daphnia and copepods until the Dap hnia stocks were depleted then switched to benthic prey. Small age-0 g izzard shad primarily selected Daphnia and copepods while larger indiv iduals consumed fewer zooplankton and more phytoplankton. Data from 19 84 through 1993 indicated no direct effect of interspecific competitio n on growth rates of either species. The decrease in Daphnia populatio ns in years with abundant age-0 gizzard shad occurs later in the year than in years with abundant age-0 yellow perch, and we suggest that th is timing is crucial for the outcome of fish interactions. When Daphni a decline later in the season, larger age-0 yellow perch can switch to benthic prey and larger age-0 gizzard shad to phytoplankton; thus, th e outcome of these interactions differs from the depression of age-0 b luegill (Lepomis macrochirus) by competition from age-0 shad reported from many reservoirs.