Movement and Recolonization of Potomac Sculpin in a Virginia Stream

Abstract

Movement patterns of benthic fishes have not been widely studied, but an understanding of those movement patterns may be necessary in assessing the full effects of habitat fragmentation and the need to restore connectivity in fragmented watersheds. We evaluated nonspawning movement of 3,353 marked Potomac sculpin Cottus girardi over a 1-year period on a 3.14-km segment of a third-order stream. In addition, we conducted a fish removal experiment at the pool–riffle sequence scale (90 m) to evaluate the effects of fish density on movement and recolonization rates. The majority of recaptured Potomac sculpin stayed within 30 m of their original capture location throughout the study (81% at 30 d; 64% at 75 d; 53% at 363 d). Upstream (US) movement was greater than downstream (DS) movement at 30 d (US 17%; DS 3%), 75 d (US 30%, DS 6%) and 363 d (US 32%, DS 15%). After 75 d, 10% of the fish that moved upstream moved more than 250 m (21% after 363 d). The maximum distance moved was 1,711 m in 75 d. There were no significant differences in mean total length between recaptured Potomac sculpin that either moved or did not move or between upstream and downstream movers. The presence or absence of fishes in adjacent 30-m habitat sections influenced upstream, but not downstream, movement of Potomac sculpin. After 30 d, Potomac sculpin population densities and size structure were similar between fish removal and reference sections. We found our results to be similar to those of other studies, which found that, on average, freshwater sculpin are sedentary. However, we identified great dispersal capabilities (>250 m) for a small percentage of Potomac sculpin. The long dispersal distances suggest that this typically sedentary species may need greater habitat connectivity than previously assumed.