Fishery-related injury in target species is rarely quantified but may be an important source of mortality in heavily exploited stocks, with consequences for management where stocks are maintained at explicit targets. Many Pacific salmon gill net fisheries are managed for escapement. While most fish intercepted by the fishery are harvested, many disentangle from nets and are counted as part of the aggregate escapement of viable spawners, regardless of their condition. If a significant portion of the run enumerated at escapement towers fails to spawn, such escapement estimates confound analyses of the relationship between spawning stock size and future recruitment. Where delayed mortality in escaped stocks is constant, this loss may be implicit in the stock-recruit function. In fisheries where effort is variable, however, dependent on run size, run timing and size of fish, fishery-related delayed mortality should be explicitly considered. We characterized fishery-related delayed mortality in sockeye salmon (Oncorhynchus nerka) to better inform escapement estimates in terms of viable spawners. Sampling multiple discrete spawning populations in Bristol Bay, Alaska, we estimated the incidence and severity of injuries in fish returning to natal streams and applied a mark-recapture likelihood model to determine the effects of such injuries on pre-spawning mortality.

Results/Conclusions

Our findings suggest that gillnet injuries are common (18%) and inhibit spawning in most (54%) injured fish. Severity of gillnet injury was strongly associated with fungal infection and reduced longevity and stream residence time, with 42% of gillnet marked fish never entering spawning areas. Gillnet injury also delayed stream entry and inhibited the development of morphological traits associated with sexual maturity. Gillnet injury disproportionately impacted large males and may compound harvest-related selective pressures that disadvantage a lifehistory of longer ocean residence. We found that stock-recruit models that recalibrate estimates of effective spawning populations by discounting actual spawners according to fishing intensity generally provide more accurate estimates of production in recruits per spawner. These results suggest that escapement figures for exploited stocks of salmon that do not account for fishery-related mortality likely overestimate the true number of viable spawners. The effects of such unaccounted mortality may have important implications for the designation of optimal escapement targets in exploited populations, the estimation of spawner-recruit relationships, and evolutionary processes driven by fishery selection.