Trapping Effects and Fisheries Research: A Case Study of Sockeye Salmon in the Wenatchee River, USA

Trapping facilities are regularly used to achieve a variety of fishery research and management goals. Though care of sampled organisms is a central tenet of most agencies, the effects of trapping on fish behavior are seldom quantified. We used passive integrated transponder technology to calculate passage delay and blockage of adult Sockeye Salmon at a facility where all spring-migrating fishes were trapped for research between 2008 and 2010. Median passage delay ranged from 0.4 to 8.7 days, and 8% to 38% of the return (2,387 to 21,090 adults) was precluded from reaching upriver spawning habitat. A protocol limiting trapping to less than 24 h per week was implemented in 2011 and median delay decreased to 6 min, with the result being that nearly all fish were able to ascend to spawning grounds for two consecutive years. The annual variation in delay was unrelated to run size or river flow, indicating that research activities requiring intensive trapping operations had inadvertently blocked tens of thousands of adult salmon from reaching spawning tributaries. We use this case study to advocate the adoption of a precautionary approach where trapping of adult migratory fishes is proposed but the effects are unknown.