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

The Ozarks hosts a diverse fish community and several endemic species due to karst features creating numerous thermal/physical habitats. Shifts in temperature and precipitation due to climate change could affect fish abundance and range through reduction of habitat heterogeneity; however, springs may mitigate these effects. In 2011, we examined the use of large springs and the timing of movement to/from these habitats by an indicator species, 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 of these moving more than 53 km. When river temperatures dropped below that of Big Spring in autumn, fish began returning to the spring.  Data on temperatures in springs and rivers coupled with fish movement data within these habitats will be crucial for detecting the effects of climate change on these thermal refugia.