The Effects of Cool and Variable Temperatures on the Spawn Date, Growth and Overwinter Mortality of a Warmwater Fish in Small Coastal Embayments of Lake Ontario

Coastal embayments have been and will continue to be constructed in the Great Lakes, however, little is known about the warmwater fish that occupy these embayments. Using pumpkinseed as a model warmwater fish, we compare growth, spawn dates and overwinter survival in two embayments with higher and lower amounts of cold-water input from Lake Ontario. In 2007, the embayments differed by approximately 2-5°C until late-July. Smaller mature pumpkinseed (57-79 mm) occupied the cooler embayment and they delayed spawning until late-summer (July 18 – August 20), too late for their offspring to grow large enough to survive the winter. In 2008 both embayments had similar temperatures. In this year, larger pumpkinseed (75-149 mm) occupied both embayments and they spawned in early-June, allowing their offspring to grow large enough to survive the winter. Using water temperature records to predict daily growth rates, we calculate that many constructed embayments are too cold to produce successfully overwintering age-0 fish. Nevertheless, we find pumpkinseed age >1 in embayments too cold to produce age-0 pumpkinseed, indicating immigration from source embayments.