Predation on Mysis relicta by Slimy Sculpins ( Cottus cognatus) in Southern Lake Ontario

Abstract

Mysis relicta and Diporeia dominated the diet of slimy sculpins ( Cottus cognatus) caught at depths of 55, 75, and 95 m at two locations in southern Lake Ontario. Length of prey was positively correlated with length of slimy sculpin. At a given depth, mean length of slimy sculpins was greater at Rochester than at Nine Mile Point, and mean length increased with depth at both locations. Frequency of occurrence of Mysis in the stomachs of slimy sculpins increased with depth, whereas frequency of Diporeia generally decreased with depth. Diporeia dominated the slimy sculpin diet at 55 m, whereas Mysis dominated the diet at 95 m. Slimy sculpins, some as small as 30 mm long, fed successfully on Mysis in Lake Ontario. We suggest that extirpation of the deepwater sculpin ( Myoxocephalus thompsoni) and perhaps the coregonines ( Coregonus spp.) in Lake Ontario allowed slimy sculpins to expand into deeper areas where they could exploit Mysis. We also suggest that at depths ≥75 m in Lake Ontario, the current Mysis-benthivore link with slimy sculpins may be similar to the past when deepwater sculpins were present.