Movements of mottled sculpins (Cottus bairdii) in a Michigan stream: how restricted are they?

We monitored 94 mottled sculpins (Cottus bairdii) marked with passive integrated transponder (PIT) tags to examine seasonal movement patterns. High detection efficiency (mean +/- standard error = 0.76 +/- 0.03) of PIT-tagged fish was obtained with a portable antenna. Nighttime searches were more effective than daytime relocations in summer, and smaller fish (<65 mm) were detected more readily than larger fish (>= 65 mm). Sculpins used erosional habitats more than depositional habitats, particularly during summer and nighttime. Search attempts within a 150 m reach showed that displacement, mean movement distance, and home range did not differ significantly between summer and winter, suggesting that season did not strongly influence movement. Additionally, movement metrics were unrelated to sculpin size. However, supplementary searches of a larger reach (700 m) showed that 16% of PIT-tagged fish moved more than 100 m over 1 year, with a maximum displacement of 511 m, and mobile fish typically displayed upstream bias. Although most mottled sculpins in our system were relatively sedentary, a small proportion of individuals moved further than previously reported for other systems.