Energetic costs of climate change: winter temperature and hypoxia effects on reproduction of an iteroparous, cool-water fish

Background/Question/Methods The frequency of hypoxic events and short, mild winters is expected to increase with continued climate change, potentially leading to unexpected consequences for aquatic ecosystems.  In the North American Great Lakes region, historical field data suggest that such changes may in part be responsible for poor recruitment of several ecologically and economically important fishes.  Herein, we test this hypothesis using Lake Erie yellow perch (Perca flavescens), a cool-water, iteroparous benthic species that develops ovaries during winter, as a model organism.  We developed a dynamic state variable model within a bioenergetics modeling framework to test whether recent poor recruitment of yellow perch may be linked to a synergistic energetic effects of summer bottom hypoxia (i.e., reduced energy reserves available during winter for gonad growth, resultant of habitat shifts into sub-optimal thermal and feeding conditions) and winter warming (via increased metabolism and subsequent reduction in energy available for gonad growth) on reproduction.  

Results/Conclusions

Our model calculated optimal energy allocation strategies for females representative of Lake Erie’s spawning yellow perch population during historically typical distributions of summer hypoxia and winter conditions.  We then simulated yellow perch energy allocation and reproductive potential using these strategies under both current and future (i.e., predicted by climate change models) environmental conditions, to gain insight into the potential bioenergetic costs of climate change.  We modeled energy allocation to structural growth, fat reserves, and gonads during winter given (1) energetic condition entering the winter (a function of extent of hypoxia during the previous growing season), (2) winter temperature regime, and (3) prey availability during the winter.  The optimal allocation pattern was that strategy that resulted in the highest expected lifetime fitness (i.e., total number of eggs produced).  Preliminary results indicate that short winters result in similar amounts of energy allocated to ovaries as in long winters; however, when condition entering the winter is poor and winter prey resources are low, reproductive development is abandoned during both warm and cold winters.