Distribution, Density, and Size of Migratory and Fluvial Sculpins in Relation to Barriers in Puget Sound Lowland Streams

Abstract

We examined the effects of potential barriers on populations of migratory sculpins (Coastrange Sculpin Cottus aleuticus and Prickly Sculpin C. asper) and fluvial sculpins (Riffle Sculpin C. gulosus, Shorthead Sculpin C. confusus, and Torrent Sculpin C. rhotheus). Barriers can alter sculpin distribution because migratory sculpins have pelagic larvae that drift downstream to calm waters and juveniles and adults migrate upstream. We compared sculpin populations upstream and downstream of a barrier in 19 lowland streams in the Puget Sound region, Washington. Within each stream, we examined the farthest downstream barrier that would be most likely to impact the upstream movements of migratory sculpins. All study streams had populations of migratory sculpins in stream reaches downstream of the barrier. In 8 of the 19 streams with a barrier, at least one species of fluvial sculpin was also present. We also documented the relative distribution of migratory sculpins and fluvial sculpins in one reference stream without a barrier. In all streams examined, the density of migratory sculpins upstream of the barrier was lower than that downstream of the barrier and the differences were statistically significant. In 12 of the 19 streams, migratory sculpins were not present upstream of the barrier. In streams with fluvial sculpin populations, fluvial sculpins were usually rare downstream of barriers and were statistically less abundant than upstream of the barrier. The migratory sculpins collected upstream of barriers were statistically larger than those collected downstream of barriers. In the reference stream, migratory sculpin species dominated the lower stream reaches and were gradually replaced by fluvial sculpin species in more upstream reaches. Overall, barriers appear to have an important effect on the distribution of both migratory sculpins and fluvial sculpins, which should be taken into account when assessing habitat modifications and fish communities in Puget Sound lowland streams.

Received November 4, 2016; accepted March 25, 2017 Published online June 12, 2017

ACKNOWLEDGMENTS

We would like to thank U.S. Fish and Wildlife Service (USFWS) employees Travis Hedrick, Rebecca Anderson, Julie Weaver, Kaylee Moser, Michelle Pena-Ortiz, Tim Grun, Rachel Brooks, Alex Bell, Zachary Moore, Michael Elam, Keith Sweeney, Tracy Leavy, and Scott Sanders for their assistance with the field data collections. Funding for this project was provided by King County, the U.S. Environmental Protection Agency, and the USFWS. Suggestions by Denise Hawkins (USFWS), Pat DeHaan (USFWS), Robert Mollenhauer (Oklahoma State University), George Pess (National Oceanic and Atmospheric Administration Fisheries), and two anonymous reviewers greatly improved earlier versions of the report. The findings and conclusions in this manuscript are those of the authors and do not necessarily represent the views of the USFWS.