An Engineered Natural Channel for Coho Salmon Rearing
David L. Smith, Tom W. Bumstead, and Ernest L. Brannon
Abstract.—Side channels are recognized as an important habitat component for stream resident species such as coho salmon Oncorhynchus kisutch. The objectives of this study were to (1) design, construct, and monitor a natural-like channel for rearing coho salmon, and (2) demonstrate an alternative rearing technique that could be incorporated into hatchery operations. Data on migration, growth, habitat use, and ultimately return rates were collected. A 286-m-long channel containing riffles, pools, ponds, alcoves, and abundant large woody debris was constructed. Discharge was set at 0.1 m3/s and was adjustable from 0 to 0.3 m3/s. Channel width averaged 1.2 m and had a surface area of 971 m2. Invertebrate drift was supplemented with a prepared diet. Fifty thousand eyed coho eggs were incubated in the channel. The resulting fry were enumerated at the tail works and allowed to emigrate so that fish residence in the channel was volitional. Out-migration was high initially, dropped in the summer, and spiked over a 3-d period in the fall before slowing during winter followed by a distinct spring out-migration. Habitat use was quantified through visual counts, snorkeling, and underwater video. Densities of fish were approximately seven times higher than comparable natural habitat. Smolts leaving the channel in the spring equated to 1.5 fish/m2, which is higher than most comparable natural habitat. We concluded that engineered channels could volitionally support numbers of fish at densities higher than in natural habitat, that fish behavior in them was comparable to wild fish, and that engineered channels could be used by hatchery programs thus contributing to hatchery reform.