Michael H. Gessel

Development of successful fish passage structures for downstream migrants requires knowledge of their behavioural response to accelerating flow

Fish have evolved intrinsic flight responses, allowing pre-emptive avoidance of potentially threatening situations. To direct downstream migrant fish away from deleterious conditions at dams and other barriers, mechanical devices such as travelling screens and fish bypass systems are often installed. However, field observations suggest that if these structures create areas of rapidly accelerating flow, they do not effectively guide the fish. We studied the avoidance behaviour of actively migrating fall Chinook salmon (Oncorhynchus tshawytscha) smolts in controlled experiments of low-, medium-, and high-flow accelerations. We measured the response velocity (VR) and the velocity gradient (VG) over body length. Although VR varied significantly with flow conditions and increased with increasing water temperature, the median VG at the instant at which smolts displayed an avoidance response was similar over the range of accelerating flows tested. Results from this study present the first quantitative informatio...

Juvenile Salmonid Guidance at the Bonneville Dam Second Powerhouse, Columbia River, 1983–1989

Abstract Studies of fish guidance with submersible traveling screens (STS) were conducted at the Bonneville Dam second powerhouse, Columbia River, during the 1983-1989 seaward migrations of yearling (age-1) and subyearling (age-0) salmonids Oncorhynchus spp. In 1983, the initial measurements of fish guidance levels were less than 25% for yearling and subyearling chinook O. tshawytscha and coho O. kisutch salmon and approximately 33% for steelhead O. mykiss, compared with expected levels greater than 70% for all species. Modifications based upon hydraulic models and field research were made to the trashracks, STSs, and face of the powerhouse. With these modifications, yearling chinook and coho salmon guidance levels greater than 75% were sometimes attained, but maximum steelhead guidance was less than 70%. Guidance of subyearling chinook salmon during the spring migration was as high as 60% but during the summer migration remained below 30%. Even with major modifications to the second powerhouse, fish guid...