Fall diets of alewife, rainbow smelt, and slimy sculpin in the profundal zone of southern Lake Ontario during 1994–2005 with an emphasis on occurrence of Mysis relicta

Abstract

In Lake Ontario, factors including the collapse of the burrowing amphipod, Diporeia spp., changes in the distribution and composition of the prey fish community, and occurrence of exotic cladocerans Bythotrephes longimanus and Cercopagis pengoi have led to changes in predation pressure on the remaining native profundal macroinvertebrate, Mysis relicta. We conducted a diet study on three important prey fishes, alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax), and slimy sculpin (Cottus cognatus) in 2002–2005 at depths 75–130 m along the south shore of Lake Ontario to evaluate the current role of Mysis in the diets of these species relative to earlier studies and previously unpublished data from 1994–1995. Mysis have remained an important prey item for alewife, rainbow smelt, and slimy sculpin in the profundal zone of southern Lake Ontario through 2005, indicating that the population has been able to sustain itself following the collapse of Diporeia. Although the occurrence of Diporeia in prey fish diets was minimal in 2003–2005, Bythotrephes longimanus and Cercopagis pengoi played an important role in the diet of alewife and a minor role in the diet of rainbow smelt, and may actually serve to mitigate predation pressure on Mysis, particularly in years when they are very abundant. Conversely, without Diporeia, the benthic slimy sculpin was primarily reliant on Mysis as a prey item and would be most vulnerable to a decline in the Mysis population.

Keywords:

• Diporeia
• food web
• preyfish
• Great Lakes
• Bythotrephes longimanus
• Cercopagis pengoi

Acknowledgements

We thank the crew of the R/V Kaho and the biological staff of the Lake Ontario Biological Station. We thank O. Johannsson and K. Bowen from Department of Fisheries and Oceans Canada for sharing data on dry weights of Lake Ontario Mysis. We thanks M. Bur, B. Lantry, and two anonymous reviewers for providing comments that improved this manuscript. This article is contribution 1420 of the USGS Great Lakes Science Center and contribution 245 of the Cornell University Biological Field Station.