Local Stream Temperature and Drainage Network Topology Interact to Influence the Distribution of Smallmouth Bass and Brook Trout in a Central Appalachian Watershed

ABSTRACT

We developed and validated a predictive model of water temperature that could be applied to mapped stream segments in a West Virginia. USA watershed. We then tested the hypothesis that local water temperature and the topology of stream thermal networks interact to determine the distribution of two fishes known to differ in their thermal preference—smallmouth bass (Micropterus dolomieu) and brook trout (Salvelinus fontinalis). Two measures of regional thermal topology were constructed—mean distance to the nearest five coldwater stream segments and distance to the nearest warmwater stream segment. Consistent with expectations, brook trout were more likely to be found in colder streams, and smallmouth bass were in warmer streams. However, brook trout distributions were statistically independent of the regional thermal context suggesting that regional thermal conditions have less influence on brook trout than local thermal conditions in this system. In contrast, there was a significant effect of stream network topology on the distribution of smallmouth bass. Bass were often present in coolwater streams located in close proximity to warmwater mainstems but not in coolwater streams highly isolated from warm water. Furthermore, sympatry in these two species was associated with cool- and coldwater streams located in close proximity to warmwater streams. These findings indicate that overall fish assemblage response to thermal conditions may be the result of species-specific responses to both local thermal conditions and the regional topology of cold, cool, and warmwater streams.