Springs As Thermal Refugia: Movement and Habitat Use Patterns of Smallmouth Bass in an Ozark River

The Ozarks hosts a diverse fish community and endemic species due to karst features creating numerous thermal/physical habitats. Shifts in temperature and flow due to climate or land use change could affect fish abundance/range through reduction of habitat heterogeneity. However, springs may mitigate these effects. In 2011, we examined the use of springs and the timing of movement to/from these habitats by Smallmouth Bass near Big Spring in the Current River, Missouri. We found movement between the spring and the river was driven by temperature. During winter, smallmouth bass inhabited the warmer water of Big Spring, and by March, moved into the river once temperatures were similar to the spring. Most fish moved less than 16 km from Big Spring. Twenty fish moved downstream of the spring with the largest movement of 51 km. Ten fish moved upstream of the spring with four moving more than 53 km. When river temperatures dropped below that of Big Spring in autumn, fish began returning to the spring. Our data suggests that springs act as winter refugia for Smallmouth Bass and possibly other centrarchids. It is critical that springs be protected to maintain thermal habitat heterogeneity needed for native fishes in Ozark rivers.