Oregon Sea Grant

Feeding selectivity was compared between slimy sculpin Cottus cognatus and deepwater sculpin Myoxocephalus thompsonii collected from southeast Lake Michigan during 1999–2002 to evaluate the hypothesis that differential prey selection contributes to long-term coexistence of these species. Study results indicated that slimy and deepwater sculpin select different prey types and sizes. Selection for the shrimp-like crustacean Mysis diluviana was consistently greater for deepwater sculpin than for slimy sculpin, whereas selection for the amphipod Diporeia spp. was higher for slimy sculpin than for deepwater sculpin when Mysis was the only other available prey type. Slimy sculpin also exhibited higher selectivity for chironomids (order Diptera, family Chironomidae) compared with deepwater sculpin. Patterns in food resource partitioning were consistent between sampling periods covering different locations, seasons and depths, as well as between locations with varying levels of Diporeia availability. This consistency suggests (1) that differences in food use by the two species are associated with intrinsic differences in food preferences or feeding behaviors and (2) that Diporeia declines had not fundamentally altered the resource partitioning dynamics of the two species as of 2002. The results also indicated that slimy and deepwater sculpin can partition food resources on the basis of prey size since deepwater sculpin tended to select larger Diporeia than slimy sculpin. Differences in prey selection may mediate competitive interactions between slimy and deepwater sculpin directly by reducing diet overlap in areas of sympatry or indirectly by causing these fish to select different depth habitats.