Why is Bristol Bay’s salmon run so resilient?

By Rod Fujita and Merrick Burden

Editor’s note: This is the fifth in a multi-part blog series, Fisheries for the Future, examining the impacts from climate change on global fisheries and the opportunities to address these emerging challenges. Throughout the series, we’ll be investigating how climate change will impact the world’s supply and distribution of fish and what we can do to ensure the most sustainable future for ourselves and our planet. Learn more about this work: Resilient Seas

Bristol Bay, Alaska, supports the largest sockeye salmon fishery in the world. The annual salmon run is often described as one of the greatest wildlife migrations on Earth. This salmon run has a large economic impact, generating over $280 million directly to fishermen and supporting about 14,000 seafood-related jobs. This is in addition to the important subsistence and cultural role it plays for many communities in the region. Bristol Bay salmon have remained abundant for over a century despite intensive fishing and climate change. Why?

Diversity matters a lot for the resilience of salmon stocks and fisheries. Five major rivers drain into Bristol Bay, and each river system contains a number of tributaries with high levels of habitat complexity. There are also five distinct salmon species that return to the system at various times of the year. Within each species and river system, there are many genetically distinct subpopulations. This diversity in habitats, run timing and genetics seems to be critical for hedging against catastrophic declines in salmon abundance.

In the Bristol Bay watershed, natural disturbances occur fairly frequently. Trees and rocks fall into rivers, altering small patches of habitat. Earthquakes and floods change large swaths of habitat pretty dramatically. Very high temperatures have been recorded in some habitat patches, perhaps reflecting climate change impacts. In some cases, certain habitats don’t change much in response to disturbance, but in other cases habitat quality — and hence salmon survivorship and abundance — has declined drastically within habitats. Sometimes, an entire river system becomes less amenable to salmon production and so the run size decreases in that river. Nevertheless, regardless of the scale of disturbance, the system as a whole — and the salmon within it — has remained very productive.

One factor that contributes to the ecological resilience of this system seems to be that the habitat patches undergo change and adaptation naturally. For instance, habitat areas will accumulate materials and energy and become relatively stable. This is followed by a disturbance of some kind (earthquake, high water, etc.) and a subsequent release of the accumulated materials and energy. The system then reorganizes itself — sometimes basically the same habitat reappears in the same place and sometimes new habitats are created elsewhere. Importantly, the habitat patches undergo these cycles at different times. Of equal importance is the lack of anthropogenic stresses (other than climate change) that disrupt the natural processes that form habitat and give rise to the complexity, diversity and variation necessary for resilience.

It would be impossible for humans to manage the extremely heterogeneous habitat patches that make up the habitat mosaic of the Bristol Bay watershed better than nature does. Instead, the state and local communities oppose activities that would reduce heterogeneity (pollution, dams, levees, etc.) and habitat quality. The community is united in resisting development (like the Pebble Mine) that would disrupt the natural processes that shape diversity and productivity in the system. However, recent developments at the federal level have drastically increased the risk of mine development in spite of local opposition. Such a development poses an enormous risk to the continued ability of the Bristol Bay ecosystem to support the abundance of salmon we have come to know and expect.

Notwithstanding the threat posed by a development like the Pebble Mine project, the Bristol Bay watershed is managed primarily to maintain natural processes and structures to support the salmon run and the associated fishery, which is the main source of employment, revenue, culture and sustenance for the entire region.

It is possible that there are several trade-offs associated with this kind of management. One trade-off might be high volatility in some places in exchange for the resilience of the salmon population as a whole. For example, in 2018 Lake Beverly (only 0.01% of global salmon habitat) produced 13% of global wild salmon yield. Other trade-offs exist where some salmon yield may be forgone when fishery restrictions are put in place in order to meet upriver salmon escapement goals (the number of fish that must escape the fishery and return to inland habitats to spawn each year in order to maintain desired yields over the long term).

Alaska strives to achieve its salmon population sustainability goals in several ways. They use habitat carrying capacity models, set escapement goals, project population size, monitor the exploitable population in real time, engage in in-season management measures, adjust season length, limit effort and make other changes to control fishing mortality.

This comprehensive management strategy requires the capacity to plan, project into the future, monitor performance of the fishery and rapidly adjust management measures — all hallmarks of a management system that helps foster resilience. It also reflects some degree of humility and an acknowledgement of the limits of predictability, meaning that management measures are not set based just on model projections, but rather on a combination of projections and real-time fish counts.

There are several other aspects of this social-ecological system that may contribute to its resilience. The strength of the salmon run is very salient and observable by all, providing feedback to fishery stakeholders about the efficacy of management and their own fishing practices. There is also a collective memory of the overfishing, stock depletion and fishery collapses resulting from a more shortsighted management approach enacted prior to statehood in 1959. The fact that the current management system focuses on salmon escapement is associated with abundant runs for decades following statehood. This helped engender faith and trust in the current management system and contributed to the enshrinement of these management principles in the state’s constitution.

The ecological resilience of the Bristol Bay system appears to be related to the high degree of genetic diversity within the salmon meta-population, habitat patchiness and un-synchronized adaptive cycles that occur within the habitat patches. Policymakers add to the resilience of the system by ensuring that salmon management focuses on sufficient numbers of salmon returning each year to spawn, rather than on maximizing yield. There is widespread trust in this management approach due to recent successes and a memory of early fishery failures due to more shortsighted approaches. Our experience here gives us one example of what ecosystem resilience looks like, and how that resilience can be supported by the people who depend on the resource most.

Stay tuned for more stories of fisheries resilience in this series. We are looking forward to working with stakeholders to help ensure that future fisheries and fishing communities are resilient to climate change.

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