The Fish Trap from North Fork Studios on Vimeo.
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.
