A new study, led by researchers at Simon Fraser University and the Department of Fisheries and Oceans, reveals the trade-offs of fish biodiversity – its costs and benefits to mixed fisheries – and points to a potential way to exploit fish. benefits while avoiding costs for fishing performance.
Many Pacific salmon fisheries capture fish from multiple stocks (management units), often representing locally adapted populations, in so-called mixed fisheries. The fish are intercepted in the ocean as they migrate along the coast, returning to different rivers to spawn.
The study used computer models of hypothetical fisheries and case studies of three actual sockeye fisheries, including the Fraser River fishery in British Columbia, to explore how fish biodiversity within mixed-stock fisheries influences both fishing performance and conservation risks.
“Our article points out that biodiversity in fisheries can offer benefits by stabilizing catches from year to year, just as a diversified stock portfolio offers more stable returns to the investor,” says the principal investigator of the article, SFU Biological Sciences Professor Jonathan Moore. “But this comes at the cost of an increased risk of extinction for individual populations and a decrease in the amount that fisheries can harvest without risking long-term sustainability.”
This is because mixed stock fisheries kill populations that may have different levels of productivity; some are considered “strong”, with high returns of adult spawners and high population growth rates, while others are “weak” and more at risk of being fished at low levels or of extinction.
Moore says, “In any major salmon watershed, like the Fraser, there can be more than a dozen different populations that have different productivities and whose yields vary asynchronously from year to year. ‘other. This remarkable diversity of salmon is a challenge for the sustainable management of fisheries.
A way forward for mixed fisheries
How then can the fishery be sustainable, in places like the Fraser River, by conserving or replenishing and benefiting from the diversity of stocks?
When fisheries can target fish from individual productive stocks while avoiding capturing unproductive and weak stocks, they can avoid many pitfalls of mixed fisheries. This high degree of management control can allow fisheries to maintain high harvest rates while reducing conservation risks.
“Whether it’s the use of genetic stock identification to inform in-season fisheries management or the resurgence of terminal salmon fisheries by First Nations, there are many ways salmon fisheries could increase their ability to target specific stocks, ”says Moore.
When opportunities for increased management control are not available, fisheries managers face the difficult task of balancing the need for crops that support fishermen with the risks of overfishing weak stocks. Often fishing rates are lowered to reduce conservation risks, but this comes with a trade-off between potential missed opportunities for high catches of fish from thriving stocks.
“In situations where there is no opportunity for increased management control, there is no single right answer and it is therefore essential that the nature of the trade-off between harvesting mixed stocks and the risks conservation is understood, so that decision-making is as informed and transparent as possible, ”says Brendan Connors, DFO research scientist and co-author of the article.
Although the paper focuses on the very diverse Pacific salmon fisheries, it has broad implications for mixed-stock fisheries in general, ranging from inshore salmon to deep-sea longlines to bottom trawl fisheries.
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