The effects of cool and variable temperatures on the hatch date, growth and overwinter mortality of a warmwater fish in small coastal embayments of Lake Ontario

► Warmwater fish ecology in coastal embayments of the Great Lakes is poorly understood. ► We use a warm and cooler embayment to evaluate warmwater fish thermal habitat quality. ► Cool temperatures delay pumpkinseed hatch and can prevent survival over the winter. ► The presence of age ≥ 1 pumpkinseed in very cold embayments suggests a metapopulation. ► 21-years of historical data confirm the findings from the two embayments.