Large Wood and Instream Habitat for Juvenile Coho Salmon and Larval Lampreys in a Pacific Northwest Stream

Abstract

The influences of large wood on Pacific salmon are well-studied, but such studies on nonsalmonid species such as lampreys are uncommon. To address this need, we evaluated the potential effects of large wood on larval lampreys (Pacific Lamprey Entosphenus tridentatus and potentially Western Brook Lamprey Lampetra richardsoni) as well as on juvenile Coho Salmon Oncorhynchus kisutch in a small, coastal, Oregon stream. Our objectives were to (1) identify instream habitat characteristics associated with the presence of larval lampreys and abundance of juvenile Coho Salmon and (2) evaluate how these characteristics were associated with instream wood. To address habitat use, we quantified presence of larval lampreys in 92 pools and abundance of juvenile Coho Salmon in 44 pools during summer low flows. We focused on a study reach where large wood was introduced into the stream between 2008 and 2009. Results indicated that presence of larval lampreys was significantly associated with the availability of fine sediment and deeper substrate. The abundance of juvenile Coho Salmon (fish per pool) was strongly associated with pool surface area and to a weaker extent with the proportion of cobble and boulder substrates in pools. Pools with wood, regardless of whether they were formed by wood, had significantly greater coverage of fine sediment, deeper substrate, and greater pool surface area. Taken together, these results suggest that instream wood can provide habitat associated with the presence of larval lampreys and greater abundance of juvenile Coho Salmon.

Received September 11, 2016; accepted March 25, 2017 Published online May 31, 2017

ACKNOWLEDGMENTS

We thank all the volunteers and technicians (Ben Ramirez, James Pearson, and Levi Pienovi) who worked on this project. This project was made possible by funding and support from the U.S. Bureau of Land Management, the Columbia Habitat Monitoring Group, the National Science Foundation Graduate Research Fellowship Program, Oregon State University, the Partnership for the Umpqua Rivers, and the U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center. Insightful comments from three anonymous reviewers and M. Fitzpatrick improved earlier drafts of this paper. Authorizations for this work included an Animal Care and Use Permit (ACUP 4211) issued by the Oregon State University Institutional Animal Care and Use Committee and a Scientific Take Permit (number 16841) issued by National Marine Fisheries Service and Oregon Department of Fish and Wildlife. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.