Winter Warming Effects on Yellow Perch Reproduction and Recruitment by:

Climate change is expected to affect fish populations worldwide through a number of mechanisms. To help understand consistent, failed Lake Erie yellow perch (Perca flavescens) year-classes following warm winters during 1975–2010, we used a combined laboratory-experimental and population-modeling approach. We hypothesized that climate change would negatively affect yellow perch by 1) increasing bottom hypoxia (O2 < 2 mg/L) during summer, which can reduce energy reserves (fish condition) prior to winter, when ovaries develop for this species, and 2) increasing winter water temperature, which could increase basal metabolic rates during winter (i.e., reduce energy available for ovary development) and disrupt thermal requirements necessary for proper ovary development. Our laboratory experiment quantified the independent and interactive effects of winter duration (number of days < 5°C: levels = 50, 80, and 110 d) and energetic condition entering winter (high, low) on reproductive development, fecundity, spawning, egg hatching and quality, and larval quality of both domestic and wild adults. Results indicate that, relative to eggs produced by Lake Erie females in the short-winter treatment, those in in the long-winter treatment produced larger, higher quality eggs that contained more calories, total lipids, neutral lipids, and myristic acid (i.e., a saturated fatty acid) per egg. These higher quality eggs also experienced greater hatching success and produced larger larvae than eggs from Lake Erie females exposed to a short winter. While long winters positively affected egg and larval quality, we found no effect of female body-condition on reproductive output, quality, or hatching success in our experiment. Using relationships among winter duration, female size, total fecundity, egg mass, and hatching success that were derived from our experiment, as well as historical adult yellow perch age-structure and winter temperature data, we developed a statistical population model to determine if winter temperature could explain historical (1975-2010) variation in Lake Erie yellow perch year-class strength, through its effects on total larval production. Finding that this annual index of total larval production was able to explain a significant amount of variation in observed year-class strength, we then used our model to forecast future year-class strength given predicted mid-century (2046–2065) winter temperatures under three commonly used scenarios (high, 1B; moderate, A2; and low, B1) of projected greenhouse gas emissions. Analysis of probability distributions generated for each future scenario suggests that continued winter warming would lead to reduced egg hatching success, with the largest decline in hatching success predicted under the highest emission scenario. Taken together, our experiment and modeling indicate a novel mechanism by which climate change can affect reproduction and recruitment of yellow perch in Lake Erie and potentially of other cooland cold-water fishes that develop ovaries during winter.