INFLUENCE OF NEARSHORE STRUCTURE ON GROWTH AND DIETS OF YELLOW-PERCH (PERCA-FLAVESCENS) AND WHITE PERCH (MORONE-AMERICANA) IN MEXICO BAY, LAKE-ONTARIO

The growth diets of 969 yellow perch (Perca flavescens) and white perch (Morone americana) caught at 3.3 and 7.0 m depths were compared between two cobble/rubble shoals and two featureless sand sites in Mexico Bay, eastern Lake Ontario during 1981. The growth rate of both species was significantly greater for individuals captured over the cobble/rubble shoals. Females of both species were faster growing than the males, although only significantly so in the white perch. The seasonal diet and breadth of diet (H') of yellow perch and white perch were not substantially different with respect to substrate type. Diet overlap between substrate types was also equivalent for each species. Benthic invertebrates, primarily Gammarus spp., were the major prey of both species at all sites. Alewife eggs were the most important item for the white perch in mid-summer, and alewife juveniles were important to both species in the fall. Differences in growth patterns between cobble/rubble shoals and sand sites illustrate a subtle effect of habitat on these species.