Do lake-specific characteristics mediate the temporal relationship between walleye growth and warming water temperatures?

Walleye (Sander vitreus) population declines have been linked to climate change, but it is unclear how the growth of this cool-water species may be affected by warming water temperatures. Because warming rates vary among lakes, it is uncertain whether lake characteristics may mediate the temperature effects on walleye growth or may vary as a result of differences in lake habitat or productivity. In this study, we (i) quantified walleye annual growth from 1983 to 2015 in 61 lakes in midwestern United States; (ii) estimated the relationship between annual early life growth (ω; mm·year^–1) and water growing degree days (GDD); and (iii) identified lake characteristics affecting log_e(ω)–GDD relationships. On average, ω estimates significantly increased with increasing GDD; however, this relationship varied in direction and magnitude among lakes. We estimated an 84% posterior probability of a negative effect of water clarity on the log_e(ω)–GDD relationship, suggesting that water clarity may mediate the effect of warming water temperatures by affecting the magnitude and direction of the log_e(ω)–GDD relationship. Our results provide insights into the conservation of cool-water species in a changing environment and identify lakes characteristics in which walleye growth may be more resilient to climate change.