Benefits and limitations of increasing the stock-selectivity of Pacific salmon fisheries

Abstract

Population diversity can stabilize ecological dynamics and increase resilience to future environmental change. In exploited systems, however, management goals to preserve diversity may be in tension with harvest objectives. For example, fisheries managers may forgo opportunities to sustainably harvest abundant populations to reduce risks to less productive populations. Increasing the stock selectivity of fisheries is one management lever that may allow for both conservation- and catch-based objectives to be met. We developed a model that simulates the dynamics of a Pacific salmon stock aggregate and its fishery to evaluate how changing allocations between mixed- and single-stock fisheries influences management performance. We focused on relatively generic management strategies that may be implemented in a range of salmon fisheries. Additionally, we examined how the relative performance of mixed- and single-stock fisheries may change under alternative ecological and management scenarios. We found that increasing single-stock fishery allocations increased aggregate abundance and improved the status of some stocks relative to their conservation benchmarks. However, these improvements did not occur uniformly–relatively abundant, productive stocks exhibited no change, or even declines, in conservation performance as single-stock fishery allocations increased. Furthermore, differences in performance between mixed- and single-stock fisheries were reduced when productivity was uniformly low, when the mixed-stock fishery was managed conservatively, or when mortality during freshwater migrations was high. While single-stock fisheries can increase the probability that conservation-based objectives will be met, they are not a panacea and may only be effective when specific conditions are met.