Graduation Date

Summer 2021

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Fisheries

Committee Chair Name

Darren Ward

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Alison O'Dowd

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Mark Henderson

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Affiliation

Community Member or Outside Professional

Subject Categories

Fisheries

Abstract

In the Pacific Northwest, the human-caused reduction of quality and quantity of freshwater rearing habitat is a limiting factor for Pacific Salmon populations. Beaver dam analogues (BDAs) increase suitable rearing habitat for juvenile salmonids and promote the restoration of critical stream processes. Installing BDAs is an increasingly popular alternative to more intensive restoration techniques, due to the relatively low cost and effort required to install BDA structures. However, widespread installation of BDAs has been slowed by regulatory agencies’ concerns that BDAs may impede fish passage. Few studies have empirically assessed the extent to which BDAs impede fish passage, and no studies have elucidated physical factors (e.g., jump height, pool depth, water velocity, etc.) that affect passage. This knowledge gap in the scientific literature warrants further investigation to discern the suitability of BDAs for future restoration and/or to improve suitable fish passage conditions. Accordingly, I quantified the ability of Coho Salmon (Oncorhynchus kisutch) and steelhead trout (O. mykiss) to bypass beaver dam structures by conducting field experiments on existing BDAs and controlled hatchery experiments. All barriers tested in the field had some level of successful passage, but passage was variable. Even the smallest Coho Salmon tested in the field could pass barriers of 36.5 cm. During the early, middle, and late summer experiments, the passage rates were 76%, 73%, and 21%, respectively. Low passage rates observed during the late summer were likely affected by fish behavior and natural adaptations to low-flow environmental conditions rather than just the barriers imposed by the BDAs; these factors should be considered when evaluating BDA fish passage. Passage rates changed with short-term changes in stream flow and available passageways. In general, passage of BDAs in the field was not limited when side channels or weir flow jump points were connected and accessible to fish. During the hatchery experiments, juvenile steelhead trout were able to pass the BDA-like structures that were constructed in the Humboldt State hatchery raceway. I tested jump heights of 24 cm, 34 cm, 40 cm and 44 cm, and passage rates were 76%, 55%, 45%, and 36%, respectively. When steelhead trout were smaller (~55 mm on average), jump height had a clear impact of passage success, but the passage rates were much more similar by the end of the trials when fish were larger (~82 mm on average). Given the benefits of BDAs and the leaping ability of juvenile salmonids, a jump height of about 30 cm might be a reasonable target for ensuring BDA fish passage.

Citation Style

Chicago Manual of Style 17th edition

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