Why the 'Portfolio Effect' Makes Bristol Bay Worth Protecting

Why the 'Portfolio Effect' Makes Bristol Bay Worth Protecting

In January, a proposed Pebble Mine in the heart of Bristol Bay, Alaska, appeared to have its fate sealed by an Environmental Protection Agency veto. The mine and the veto are old news by now (here’s an overview if you’re not up to speed), but the minerals and the threat of mining aren’t going anywhere.

Pebble is bound to resurface eventually, but when it does, it’s worth knowing why mining in Bristol Bay is a bad idea—from a biological and conservation standpoint. That’s not to say all mining is bad—the United States needs minerals, metals, and oil to run—but the common, “wrong mine, wrong place” slogan in the fight against Pebble was remarkably well-supported by a robust scientific basis.

If anyone knows a thing or two about the issue, it’s Daniel Schindler, a University of Washington-based professor who’s dedicated his career to field research in Bristol Bay. “People have the general viewpoint that Alaska’s so big that there’s no way we could really screw it up,” Schindler told Science magazine in the midst of the controversy in 2019.

What is ‘The Portfolio Effect?’

Indeed, the vastness of Alaska is difficult to comprehend, but look closely at Bristol Bay—the world’s single largest producer of sockeye salmon—and a different story comes into perspective. It’s one that was first fully laid out in a paper published by Schindler and his colleagues in 2010 in the scientific journal Nature. It introduces an idea called “the portfolio effect” to describe why the Bay consistently kicks out millions of sockeye annually—to the tune of 40 million on average—and powers a $2 billion commercial fishing industry.

The basic idea is that biological diversity stabilizes ecosystems. The authors use the metaphor of a portfolio of stocks: a diversity of asset buffers against market fluctuations, resulting in a portfolio that’s resilient and stable. The same could be said for Bristol Bay sockeye. It all boils down to spreading the risk—buffering against naturally-occurring or human-caused threats. This occurs at multiple scales: Bay-wide, within a single river system, and in the genetic diversity of the salmon themselves.

A Diverse Portfolio

At the largest scale, Bristol Bay is composed of nine major rivers. In any given year, a single river might have great production, cranking out millions of sockeye salmon, or be a total bust. The reasons for annual fluctuations are numerous: spawn timing, water conditions, outgoing juvenile migration, and a plethora of others. But with nine rivers producing fish, some are on the upswing and some are on the downswing annually. Together, they balance each other out, resulting in a fairly consistent overall run size. There are still a couple of anomaly years, where things align for all-time highs or all-time lows (2022 set a record high of 79 million fish; 1973 a record low of 2.5 million), but generally things are stable, and major shifts tend to occur over the course of decades or centuries, rather than on a year-to-year basis.

Broken down further is the river-wide scale. In almost all cases, sockeye salmon need freshwater lakes to reproduce—juveniles spend up to two years rearing in them before migrating to the ocean. Most river systems in the Bay contain several lakes apiece and dozens of smaller tributary creeks that are prime spawning grounds. Similar to the Bay-wide perspective, the salmon productivity of the lakes and creeks fluctuate annually but together buffer the river systems in which they’re contained. In the research paper, the authors predict that if the bay were composed of a single population of salmon, rather than dozens of smaller ones, there would be over two times the annual fluctuations in overall run size.

At an even finer scale is the diverse life history of sockeye salmon. The fish can spend either one or two years in freshwater, and then one, two, or three years in the ocean. That means a juvenile sockeye hatching out of an egg has six possible options (technically, females only have five), although it’s thought to be genetically predetermined at the individual level. This diversity is an evolutionary-derived strategy for guarding against risk. Should poor conditions in freshwater or the ocean kill the entirety of a year-class, that generation’s siblings are still alive in other areas of the watershed or the ocean. Therefore, an annual return of sockeye is actually a mix of fish born across a two to five-year period.

Big Picture Protections

Coming back out to the bigger picture, “natural ecosystems are remarkably resilient, if given the chance,” Schindler said. “So the conservation message is: give it a chance. Maintain the places that are expansive, and maintain the variation in those systems, whether it’s the habitat variation or the genetic variation.”

Bristol Bay is already one of the most highly-exploited natural ecosystems in Alaska. It’s living proof that ecosystems can function even with a heavy human impact.

“Nature is not fragile. It is resilient if you give it a chance,” Schindler said. But the key to resilience is intact habitat, and lots of it. Eat away at small chunks here or there—the proposed footprint of Pebble was only 1% of the Bay—and that diversity of habitat starts to wane. It might not result in huge, immediate impacts, but development preempts development, and before long, the cumulative sum of losses is significant.

In the Nature paper, the authors conclude, “The portfolio effects in the Bristol Bay sockeye stock complex are a characteristic of a landscape with a largely undisturbed habitat, natural hydrologic regimes and neither invasive species nor artificial propagation of salmon in hatcheries, combined with sustainable fishery exploitation.” This is a stark contrast with southern, coastal salmon populations in Oregon, Washington, and California where runs are a shadow of their former size, due to the cumulative effects of heavy fishing, habitat loss, energy development, and hatcheries.

When it comes to Bristol Bay, the science is clear. We still have the chance to protect it from the same fate as the Pacific Northwest, but it requires keeping the region as intact and unperturbed as possible.

Feature image via Tosh Brown.

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