Gill‐Net Fishing Effort Predicts Physical Injuries on Sockeye Salmon Captured near Spawning Grounds.

Nonretention in gill‐net fisheries for Pacific salmon Oncorhynchus spp. can be relatively high and can cause a variety of impairments to nonretained fish, which often lead to immediate or delayed mortality. We sought to improve the understanding of the association between gill‐net escapement and injuries incurred by upriver‐migrating salmon by examining the relationship between gill‐net fishing effort in the Fraser River, British Columbia, and the frequency and severity of gill‐net injuries to migrating Sockeye Salmon Oncorhynchus nerka. Adult Sockeye Salmon were intercepted at a location approximately 335 km from the mouth of the Fraser River and assessed for gill‐net injuries. Gill‐net fisheries targeting Sockeye Salmon operated throughout the first 320 km of the Fraser River main stem starting at the mouth of the river. A generalized linear mixed model was used to identify the role of gill‐net fishing effort, fork length, and sex on the probability of an individual fish sustaining a gill‐net injury. Predicted probabilities of gill‐net injury ranged from 12% to 46% across all levels of fishing effort, suggesting that gill‐net injuries were more prevalent among individuals that encountered high levels of fishing effort. However, fishing effort did not seem to influence the severity of gill‐net injuries. Our results suggest that estimates of fishing effort may be useful in predicting the probability of gill‐net injury to migrating fish, which could help managers estimate en route mortality and more accurately predict spawner escapement. [ABSTRACT FROM AUTHOR]