Ontogenetic Shifts in Habitat, Diet, and Diel-Feeding Periodicity of Slimy Sculpin in Lake Ontario

Abundance, size, and diet of slimy sculpin Cottus cognatus in southeastern Lake Ontario were determined from 239 bottom trawls at depths of 35 m and 75 m in June and August, and at depths of 8–75 m in October 1984. Slimy sculpin less than 50 mm total length generally inhabited water shallower than 60 m; larger fish dominated catches at 75 m. The fish at 35 m fed mainly at night; those feeding at 75 m showed no diel-feeding periodicity. More slimy sculpin were caught at night than during day at depths of 60 m or less but day and night catches at 75 m did not differ significantly. Amphipods Pontoporeia hoyi formed the main prey of all slimy sculpin; opossum shrimp Mysis relicta were eaten more often by the larger fish in deeper water than by small fish in shallower water. Data suggest that young slimy sculpin shift from a shallow water habitat and nocturnal feeding to continuous activity in deeper water as they mature. The behavior of slimy sculpin in shallower water may reflect an attempt to avoid predators during day.