Explaining variation in life history timing across a species range: Effects of climate on spawning time in an exploited marine fish

The capacity of a species to tolerate and/or adapt to environmental conditions will shape its response to future climate change including climate extremes. Of the many life-history processes affected by climate change, timing of reproduction greatly influences offspring success and resulting population production. Here we explore temporal and spatial changes in spawning time for Atlantic cod (Gadus morhua) across the species’ range (4 to 80°N). We estimate spawning time using a physiologically relevant metric that includes information on fish thermal history (degree days, DD). First, we estimate spawning DD among years (within populations) to show recent changes in spawning time can be explained by local changes in temperature. Second, we employ spawning DD to identify temperature independent trends in spawning time among populations that are consistent with the evolutionary history of the species. Combined, these results shed light on the adaptive capacity of the species in the face of changing climate. We use our results to estimate expected spawning time under future climate regimes, and discuss the implications for codecology and management across the species’ range, and in the greater ecosystem