Movement Patterns of Japanese Fluvial SculpinCottus polluxin a Headwater Stream

Abstract

AbstractMovements of the Japanese fluvial sculpinCottus polluxwere studied over a 2‐year period using a mark‐recapture technique in two reaches (100 and 300 m) of a small, temperate stream system, the Fujii River, Japan. Of 321 recaptures, 62 fish (19.3%) moved across at least one riffle (i.e., were “mobile”). Fish moved distances of up to 192 m (median = 4 m). Distance moved (m) by all fish correlated positively with the recapture interval (d) in both years, illustrating the importance of the temporal dimension for movements. Mean daily distance moved (m/d) in the high‐flow year was greater than that in the low‐flow year. The high‐flow year, which had a higher frequency of peak flow events, had a higher frequency of mobile fish than did the low‐flow year, suggesting that interannual variation in movements is related to streamflow. Fish size and growth did not differ between mobile fish and residents in the high‐flow year; however, mobile fish were larger and grew more slowly than residents in the low‐flow year. Patterns of movement from multiple recaptures showed evidence for round‐trip movements at channel unit and reach scales, but no fish completed round‐trip movements by crossing a small weir (<0.5 m in height). These results emphasize the importance of maintaining fish passage and pool‐riffle sequences throughout the stream course to prevent isolation of subpopulations by weirs, culverts, and road crossings. Physical barriers to Japanese fluvial sculpin movements could be mitigated by placing a ramp of cobbles downstream of the barriers.