Biodiversity seems, naturally, like a good thing but when it comes to fisheries management, it can involve competing trade-offs.

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A new study, by researchers from the Salmon Watersheds Lab and the Department of Fisheries and Oceans, reveals the trade-offs of fish biodiversity—its costs and benefits to mixed-stock fisheries—and points to a potential way to harness the benefits while avoiding costs to fishery performance.

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Many Pacific salmon fisheries catch fish that come from multiple stocks (management units), often representing locally-adapted populations, in so-called mixed-stock fisheries. Fish are intercepted in the ocean as they migrate along the coast, returning to different rivers to spawn.

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The study used computer models of hypothetical fisheries and case studies of three actual sockeye salmon fisheries, including BC’s Fraser River fishery, to explore how fish biodiversity within mixed-stock fisheries influences both fishery performance and conservation risks.  

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“Our paper highlights that biodiversity in fisheries can provide benefits by stabilizing catches from year to year, much like a diverse stock portfolio provides more stable returns to the investor,” says lead author, Professor Jonathan Moore. “But this comes at the cost of increases in the risk of extinction to individual populations and decreases in the amount that fisheries can harvest without risking long-term sustainability.”

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This is because the mixed-stock fisheries are harvesting populations that can have different levels of productivity; some are considered ‘strong,’ with high adult spawner returns and high population growth rates, while others are ‘weak’ and more at risk of being fished to low levels or extinction.

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Dr. Moore says, “In any given major salmon watershed, like the Fraser, there may be more than a dozen different populations that have different productivities and whose returns vary asynchronous from year to year. This remarkable salmon diversity is challenging for sustainable fisheries management.”

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How then can fisheries be sustainable, in places like the Fraser River, conserving or rebuilding stock diversity while also benefiting from it?

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When fisheries can target fish from individual productive stocks while avoiding catching unproductive, weak ones, they can avoid many of the pitfalls of mixed-stock fisheries. This high degree of management control can allow fisheries to maintain high harvest rates while reducing the conservation risks.

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Media: SFU News.