Navigating a Thermally Heterogeneous World: Smallmouth Bass in Spring-Fed Rivers

Smallmouth bass (SMB) often exist in streams that are subject to thermal variation in both space (groundwater inputs) and time (natural seasonal/diel variation and climate change).  How fish deal with these challenges is not fully understood and is the focus of our presentation.  Our objectives were to determine movement of SMB that use thermal refuge and project differences in growth and consumption for fish with different movement strategies.  Further, we wished to compare potential SMB growth under various climate change scenarios.  We implanted radio transmitters and temperature archival tags in 29 SMB in a spring-fed Ozark stream to determine movement patterns and inform bioenergetics models for growth and consumption.  We also developed a predictive stream temperature model and used forecasted temperatures developed under various climate change scenarios to examine the number of positive and optimal growth days for SMB. The longest observed movement of SMB in our system was 42.5 km, and the bioenergetics models showed potential growth differences for various movement strategies.  Course-scale shifts in species distributions induced by climate change will likely occur, but fine-scale shifts may also occur in thermally heterogeneous systems forcing SMB to occupy different sections of stream to experience optimal temperature conditions.