The Fish Trap

Bycatch mortality from gillnets and other conventional harvest techniques impedes the recovery of Endangered Species Act (ESA)-listed salmonids and commercial fishing opportunities when ESA-take limits are exceeded.

To benefit wild salmon, threatened ecosystems, and coastal fishing communities, Wild Fish Conservancy and local commercial fishermen conducted a post-release survival study in the Lower Columbia River Sub-basin to evaluate the potential of an alternative commercial gear—specifically, an experimental pound net trap—as a stock-selective, sustainable harvest technique. Expanding upon the 2016 pilot study, a modified trap was constructed and operated under a variety of tidal stages, light levels, and weather conditions between August 26th and September 29th, 2017.

Utilizing a mark-recapture methodology with Passive Integrated Transponder (PIT) tags, post-release survival from the trap was estimated by comparing tag detections at upstream dams to that of a control source of fish; total catch, catch-per-unit-effort, and covariates of recapture probabilities were analyzed. Preliminary results demonstrate that pound net traps can effectively target commercially viable quantities of hatchery-reared Fall Chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) while reducing immediate and post-release bycatch mortality of ESA-listed species relative to conventional commercial gears.

Throughout the 33-day test fishing period, the experimental trap captured and released 7,129 salmonids. Relative post-release survival ranged from 94% for steelhead trout (Oncorhynchus mykiss) to 99% for Chinook salmon. These results suggest that fish traps may provide a sustainable alternative to conventional commercial gears, enabling efficient harvest of targeted salmon stocks and recovery of ESA-listed stocks mixed within salmon fisheries.

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