Movement and Growth of Translocated Coastrange Sculpin and Prickly Sculpin in Two Urban Lake Washington Tributaries, Washington

Abstract

Abstract Urbanization and other forms of land conversion have led to dramatic changes in freshwater ecosystems. We assessed the movement and growth of Coastrange Sculpin Cottus aleuticus and Prickly Sculpin C. asper, two species that are considered migratory based on their potamodromous and amphidromous life history strategies. We determined critical aspects of their ecology in two urban streams where they are rare or absent. Both species were collected near the stream mouth or in Lake Washington, implanted with passive integrated transponder (PIT) tags, and translocated to an upper stream reach where their downstream movements and growth were monitored. Detections at stationary antennas indicated most downstream movements occurred from January to April, as has been observed in other Pacific Northwest systems. About 80% of the translocated sculpins remained in the study reach for at least 2 months before moving downstream and 10% remained more than a year. Smaller Prickly Sculpin generally remained in the study reach longer than larger Prickly Sculpin; however, no size effect was observed for Coastrange Sculpin. Most downstream movements occurred during low and moderate streamflow levels during each season for both streams; however, downstream movements occurred at relatively higher flows compared to the cumulative distribution of observed flows during most seasons. Both species appeared to grow well in the study streams; although, Prickly Sculpin growth rates were approximately double that of Coastrange Sculpin. Coastrange Sculpin often inhabit riffles where increased fine sediments and embeddedness from urbanization may impact them more than Prickly Sculpin, which typically inhabit pools. The overall survival and growth of both species in the two highly urbanized streams was better than expected. This study suggests that the lack of sculpins in some urban streams may be a result of stream barriers to movement rather than poor habitat conditions.