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Fraser River fishermen may have an Alaskan volcano to thank for this summer’s supercharged sockeye salmon run that ended up being the biggest in nearly a century.

The eruption of Kasatochi, an Aleutian Island volcano, fertilized a vast area of the north Pacific Ocean by spewing out huge amounts of iron-rich ash, according to new research presented to the Cohen Commission into sockeye stocks.

It’s one of the more intriguing ideas to arise in the hearings now underway in Vancouver.

The judicial inquiry into the collapse of the 2009 sockeye run, when just over a million fish returned, has been forced to also try to make sense of why almost 30 times more sockeye came back this year.

Kasatochi’s ash fell at precisely the right time in the summer of 2008 to create huge algae and plankton blooms that provided Fraser sockeye with a tremendously rich food source, researchers told the commission.

“There was a massive increase,” Dr. David Welch testified last week. “It was a very large eruption.”

Welch tabled satellite imagery of the ash plume and the resulting plankton bloom, which he said could well be responsible for the tremendous productivity of the Fraser sockeye run that came back this year.

The run size is estimated at 34.5 million, although officials expect the final count to drop to around 29 million.

Crucially, the eruption happened just as a major storm system was pounding Kasatochi, helping disperse the ash over a wide area of the Gulf of Alaska.

The summer timing also helped – long hours of northern sunshine grew more plankton than otherwise.

And it all happened as young sockeye from the Fraser were arriving in that part of the ocean, just in time to gorge on the fish food bonanza at a critical stage of their growth.

Scientists stress there are many other factors that could have contributed to the unusual return.

But the theory is a signal this summer’s salmon bounty was likely a fluke and not a lasting rebound – volcanic eruptions can’t be counted on for consistent help.

Sockeye returning to the Adams River northeast of Kamloops.

Also at issue in the inquiry is how far fishery managers should go in trying to protect the biodiversity of Fraser sockeye – essentially whether the weakest stocks should be sacrificed if strong runs returning to certain tributaries can sustain fishing.

The commercial fleet is sometimes ordered to stop fishing to avoid endangering weak runs like Cultus Lake sockeye, which return intermingled with more abundant stocks like the Adams River run.

Rob Morley, Canadian Fishing Co. vice-president and chair of the Fisheries Council of Canada, suggested a better way to conserve Cultus sockeye might be to ban all recreational activity on the popular boating and swimming lake.

“We are under-harvesting Fraser sockeye significantly,” he told the commission.

“If the aim is to maximize all stocks, nobody would be allowed to harvest any sockeye.”

Other witnesses argued even the tiniest runs should be defended.

The Fraser River needs a “diversified portfolio” of individual sockeye runs, the inquiry heard, because no one knows for sure which stocks will be best genetically equipped to survive future environmental conditions, such as the impacts of climate change on either the ocean or inland rivers.

It’s a sensitive point for First Nations advocates, who want to ensure a supply of salmon can be caught by local bands throughout the entire watershed.

“If some of these go extinct it means a lot to our people,” said Dr. David Close, an aboriginal fisheries expert. “We have to be very careful.”

SFU salmon expert Dr. John Reynolds warned B.C.’s wild sockeye may also be increasingly in competition for food with hatchery-raised salmon from Russia and Japan that also feed in the north Pacific.

Reynolds said both countries are dramatically increasing hatchery production.

Sockeye aren’t the only fish that have been in trouble on the Fraser.

Coho salmon were in crisis in the 1990s, Close noted, prompting severe fishing restraint.

And in more recent years, he said, a once “unimaginably abundant” run of eulachon – an oily smelt-like fish harvested by First Nations – has all but vanished.

Justice Bruce Cohen, in an interim report released Friday, said this year’s “extraordinary” rebound was in contrast to the “steady and profound” decline of sockeye over the past two decades.

The commission has so far received 153 written submissions, most addressing aquaculture issues.

Hearings are scheduled until late December.

This week, current and former managers with Fisheries and Oceans Canada are testifying about the structure of the department.

Kasatochi volcano

 

 

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