Potential Effects of Climate Change on Growth of Smallmouth Bass in Streams of the Central U.S

Smallmouth bass (Micropterus dolomieu, SMB) is a widespread species with broad distribution throughout the eastern and central U.S. and introduced populations in many regions beyond its native range.  Prior studies have shown that SMB distribution is expected to shift with predicted changes in climate, but little is known about how these changes will mechanistically affect the performance of populations.  We modeled the population-level impacts of projected climate change on growth of stream dwelling smallmouth bass along a north-south gradient in the central U.S.  We used regional climate projections and stream temperature models to generate scenarios for thermal habitat change in areas in the northern range (e.g., Minnesota) to the southern range (e.g., Missouri).  We modeled climate change based on downscaled global climate models and compared growth from current year (2010) and future (2040) projections.  Bioenergetics model simulations (based on SMB growth and diet data from published literature, agency reports, and databases) revealed how these changes may affect growth and consumption within populations.  In northern populations such as in the Upper Mississippi Basin, summer temperatures are expected to warm by approximately 2°C (currently peak near 23°C), and growth potential is predicted to increase if not limited by prey availability.  In more southern populations such as in the Missouri Ozarks, similar increases in summer temperatures are expected, but the models indicated that growth potential would decrease where stream temperatures more frequently exceed 27°C.  Our results suggest that SMB populations will respond differently to climate change along the latitudinal gradient.  Due to the direct implications for survival, reproductive fitness, and species interactions, a better understanding of how SMB growth rates will respond to climate change is vital for the management and conservation of the species.