Influences of Instream Features on the Dispersal Patterns of Darters

Understanding the dispersal dynamics of stream fishes will aid in the management of populations and in the designation of critical habitats for threatened species.  Movement studies to date have determined species- and stream-specific movement rates and home ranges, failing to elucidate the biotic and abiotic variables that could cause these parameters to vary.  To determine the influence of instream features on dispersal patterns, we studied the movements of three darter species throughout an upland Virginia watershed during the summer of 2001.  In early summer, we marked fishes at 24 sites using batch elastomer tags.  We chose sites that differed in land-use, stream size, and predator abundance.  In late summer, we recaptured fishes and tested for relations between dispersal patterns and measured instream features.  Of 589 recaptured individuals, only 26 (4%) dispersed from the riffle in which they were marked.  Emigration rate was highest at sites where considerable riffle shrinkage occurred during the summer, whereas predator abundance and stream size had no measurable effects.  Median dispersal distance was 92.4m (range 39.6 - 248.8m).  These data indicate that darters are relatively sedentary during the summer, but are capable of long-distance movement through inhospitable habitats when conditions become less favorable.