Influence of Winter Starvation on the Distribution of Smallmouth Bass among Wisconsin Streams: A Bioenergetics Modeling Assessment

I used a bioenergetics model to test whether overwinter starvation of age‐0 smallmouth bass Micropterus dolomieu , a representative warmwater species, could account for their scarcity in coldwater streams of Wisconsin. I modeled 84 combinations of food consumption rate, maximum daily mean summer temperature, and winter duration that encompassed the range of conditions likely to be encountered in Wisconsin streams, and ran simulations for the specific thermal regimes in four coldwater, one coolwater, and two warmwater Wisconsin streams where smallmouth bass population status was known. The model predicted that starvation mortality was unlikely at the highest food consumption rates, the warmest summer temperatures, and the shortest winters. Mortality increased with decreasing food consumption rates, decreasing maximum summer temperatures, and increasing winter duration. Starvation mortality was predicted to be negligible in the two Wisconsin warmwater streams, which had self‐sustaining smallmouth bass populations, and to be generally minor in the coolwater and three of the four coldwater streams, all of which lacked smallmouth bass. Only in the coldwater stream with the lowest maximum summer temperature and longest winter, a stream that also lacked smallmouth bass, was mean starvation mortality predicted to consistently exceed 30%. I conclude that, by itself, overwinter starvation of age‐0 smallmouth bass is unlikely to limit the occurrence of smallmouth bass in most Wisconsinˈs coldwater streams. The model also predicted relatively slow growth of age‐0 smallmouth bass in Wisconsin coldwater streams. Reduced growth could make age‐0 smallmouth bass susceptible to other sources of mortality (e.g., predation, displacement) and might contribute to their scarcity in coldwater streams.