This summer, Bristol Bay set a record for the largest sockeye run: 65.86 million salmon returned. That’s much higher than the pre-season forecast of 50 million salmon, and the run hasn't finished yet.
But why Bristol Bay is such a sockeye hot spot poses a puzzle for scientists.
“The question of why so many sockeye have returned to Bristol Bay the last seven or eight years is a bit of a mystery to I think most people, if not everyone,” said Daniel Schindler, a professor and ecologist in the school of Aquatic and Fishery Sciences at the University of Washington.
Schindler is also the principal investigator at the Alaska Salmon Program — a research project that has documented the watersheds surrounding parts of Bristol Bay since the late 1940s.
This was Schindler’s 25th year exploring and researching the Wood River system, one of the nine rivers feeding into Bristol Bay.
As part of the job, he spends most of his days from mid-June through mid-September walking a couple miles up and down obscure creeks and rivers, counting salmon as they return to their spawning grounds.
By the end of July, only a fraction of sockeye have returned to spawn.
“I mean this looks like a lot of fish but the peak is still about 10 days away,” Schindler said while tallying sockeye on a July afternoon.
But not every area of Alaska is seeing a lot of fish.
This summer, communities along the Yukon River saw some of the lowest Chinook and chum runs on record. Several communities have even appealed for federal aid through fishery disaster declarations.
With access to decades of data, Schindler and his colleagues are trying to make sense of what sets Bristol Bay apart.
One factor, he said, might be water temperature.
Western Alaska is one of the fastest warming places on earth, and scientists have had to re-scale their charts over the last decade to adapt.
“Climate warming seems to have actually benefited Bristol Bay sockeye — warmer temperatures, more food, more growth opportunities and they are still in the sweet spot of water temperatures that are still profitable,” Schindler said.
Video courtesy of Daniel Schindler.
Other parts of the state aren’t as lucky. Ocean waters are a few degrees warmer in the Gulf of Alaska, and that slight difference has challenged fish populations south of Bristol Bay.
Schindler said another possibility for Bristol Bay’s success is the area’s large and intact habitat. The surrounding watersheds are uninterrupted by roads, dams and other development.
“That's one of the reasons Bristol Bay is so unique, is that all of that habitat diversity is still here, and all of that genetic diversity in the salmon and life history diversity is still here,” he said. “And it's interesting scientifically, but it's also important for the fishery, because all of that diversity stabilizes how many fish come back from year to year.”
It’s normal for fish populations to fluctuate. And while at some point, Bristol Bay will likely see a smaller run, Schindler said he remains optimistic.
“It's hard to believe the 50 to 60 million fish per year that we've been seeing — never mind the 64 million fish that we've seen this year — is going to continue at that level forever," he said. "But if we look into a crystal ball for the next century and look at the fact that the world is warming, there is no reason to believe that Bristol Bay salmon populations won't continue to flourish even under substantially warmer temperatures."
But Schindler admits the ocean is a complex place full of many unknowns that scientists still don’t fully understand.
“Really the question is how much more warming these systems can withstand before they get too warm like California and other places in the Pacific Northwest,” he said.
Schindler plans to return to Bristol Bay each summer to count the salmon and better understand how the warming climate is impacting the world's largest sockeye salmon fishery.
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