Effectiveness of habitat manipulation for wild salmonids in Wyoming streams

Habitat manipulation is commonly used to enhance habitat and stocks of fluvial trout of the genera Oncorhynchus, Salmo, and Salvelinus, but questions have been raised about the effectiveness of such work. Consequently, I analyzed wild trout abundance, biomass, and habitat before and after habitat manipulations among 30 projects done by the Wyoming Game and Fish Department. Abundance and biomass of trout increased following habitat manipulation among most of the projects. Excessive angler harvest prevented an increase at three projects, and drought hindered fish response in a fourth stream. At a fifth project, the trout population decreased after intense cattle grazing degraded project structures. Instream structures proved durable. Only one project, which featured wire trash catchers in a fourth-order mountain stream, suffered failure of habitat manipulation devices. Cover for trout and residual pool depth significantly increased following projects, whereas eroding banks significantly decreased. Both timber and log check dams consistently produced good pools, but rock check dams did not. Mean per project cost statewide was US$39,230/mi. These results demonstrate that well-built, properly located, and properly maintained instream structures can provide better habitat and increase stocks of trout in carefully selected reaches, thus satisfying public and agency expectations for fishery improvement and gaining time to correct watershed problems.