Answering Growing Questions of Bluegill’s Past – Connecting Changing Body Size to 69 Years of Environmental Changes

Abstract

The differential impacts of climate and anthropogenic stressors on body size and growth are trends of interest for many ecologists studying climate change impacts. These stressors are known to be co-occuring in nature, so untangling the response of body size from one or the other causes is difficult to do without long-term datasets, which are often difficult to access. Recent digitization efforts have now opened the door to new analysis possibilities by providing historical growth data from 1950 to 2019 at 1069 inland lakes in Michigan. I combined historical data with data from recent monitoring efforts to examine changes in mean bluegill length at age. In this study I find juvenile bluegill (Lepomis macrochirus) ages one to four have experienced losses in mean body length, while mature adults ages six to eight have seen gains in body size over the same time period. Using Boosted Regression Tree models, I was able to delineate trends in growth that could be attributed to increasing temperatures and length of growing seasons, and morphological characteristics of the lakes, while also accounting for the impacts of other stressors such as land-cover changes, increasing human populations, and assemblage changes at the same time. These models explain between 22% and 61% of deviance in bluegill growth.