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NW Fishletter #282, December 10, 2010

[4] From Boom To Bloom? Federal Scientists Discount Volcano Theory

NOAA Fisheries scientists aren't impressed with a Canadian theory that suggests this year's return of 30 million sockeye to the Fraser River was helped by a 2008 volcanic eruption in Alaska.

"We're not buying into that," said Ed Casillas, an ocean researcher based at the NMFS Science Center in Seattle.

Casillas said there is no evidence that salmon stocks on our side of the border showed any off-the-chart returns like the Fraser run, which was the best since 1913, when the river was nearly blocked by a dynamite blast during railroad construction and has been recovering from that blow ever since.

In 2008--when most of this year's return of Columbia River spring chinook and those Fraser sockeye went to sea--ocean conditions off the West Coast were the most productive for salmon that oceanographers had seen in their entire careers, and waters in the Gulf of Alaska were the coldest in the last 50 years.

However, the volcano theory came to light after a Canadian commission began soliciting testimony into causes of the Fraser run crash in 2009, when about 1.5 million returned--only 10 percent of what was expected.

But the huge return to the Fraser this year has confused the issue even more. And a cursory look at salmon returns in Alaska shows no unusual spikes in returns this year, either. But there is evidence from satellite photos that the eruption helped to seed a huge plankton bloom in the Gulf of Alaska with iron from the falling ash.

Researchers have known for years that when strong westerly winds are blowing across the North Pacific, iron-laden dust from the Gobi Desert can be carried all the way to the Gulf of Alaska, where it falls into the ocean and boosts plankton growth.

NOAA Fisheries researcher Bill Peterson said the volcano theory "is not that far-fetched." He said the issue was discussed at a scientists' confab last month.

A Canadian report on 2008 ocean conditions found that "surface phytoplankton and zooplankton concentrations were the highest in a decade of observations across the Gulf of Alaska in August and September 2008. The cause is as-yet uncertain, but injection of iron by winds or currents is suspected (iron is a limiting nutrient in this region), along with higher levels of nitrate and silicate in spring."

Kasatochi volcano
Kasatochi volcano--before and after August 2008 eruption, courtesy USGS

The June 2009 report noted that "several volcanoes erupted in summer 2008 in the Aleutian Islands, so volcanic dust is a possible source of iron, but it is not easily spread over the entire gulf by winds alone. Unusual currents in the summer of 2008, which could have transported either volcanic or oceanic iron from the Alaskan Peninsula into mid-gulf, are described in the report on flow in the North Pacific Current."

NOAA oceanographer Peterson said it takes about a month for the kind of zooplankton fish like to eat to materialize from the plant-like phytoplankton that had covered the Gulf.

However, he said, by September, the zooplankton drops down into the deep ocean for the winter, and salmon stop feeding on it until the next summer, when it rises again toward the surface. So, the August plankton blooms would have occurred fairly late for salmon to have gained much benefit.

Peterson said it probably had some positive effect, but it would be hard to prove, judging from other salmon returns. But the retired fisheries professor who suggested the link between the Fraser sockeye boon and the volcanic boom thinks otherwise.

Prof. Timothy Parsons, from the University of British Columbia, told NW Fishletter by email that he believes the Alaska and Columbia River runs were not affected because "they feed much more in a coastal regime which has lots of iron. These runs can certainly vary but under a different set of rules to the open ocean fish."

Parsons' volcano theory is based on a recent paper in Geophysical Research Letters, by Roberta Hamme and others, linking the August 2008 eruption to a huge phyotoplankton bloom later that month.

He has sent his comments to the commission looking into the 2009 run failure.

"It has been presumed previously," said Parsons, "that all the West Coast salmon just went out to the Gulf and fed randomly--not true--very few if any fisheries biologists ever go to sea! If they did, they would have collected salmon at sea and using radioisotopes they might show (as we did) that like all other migratory animals, salmon go and come to specific locations in the Gulf. Hence Columbia River salmon are probably not feeding in the same place as various stocks of the Fraser."

But high-seas-salmon tagging reports show a considerable overlap in areas where immature sockeye from Bristol Bay and other Alaska stocks and B.C. sockeye are found, said University of Washington researcher Kate Meyers.

She noted that immature Bristol Bay stocks actually had a higher offshore distribution than the Canadian sockeye, according to a report that included data from 1995--the latest available on the Fraser stocks.

Other Canadian scientists agree, including retired DFO biologist Brian Riddell, now executive director of the Vancouver, B.C.-based Pacific Salmon Foundation.

Riddell said there isn't much evidence showing the sockeye runs don't share the larger, open part of the Gulf of Alaska.

Though the different stocks may not be in the same place at the same time, if the volcano was a big factor, he said there should be more evidence of it in other fish returns.

Riddell pointed out that northern B.C. sockeye runs showed no evidence of it. He said it's likely the Alaska volcano, and an earlier eruption in Russia, improved productivity for many salmon stocks in the Gulf, but it wasn't likely that the Fraser sockeye got more help than other runs.

Another Canadian scientist, Randall Peterman of Simon Fraser University, told Nature.com recently that 15 of 18 salmon populations sharing Gulf waters showed no unusually high returns this year, although three did. He said it was more likely that the large return occurred because of higher survival near the coast.

Prof. Parsons said he doesn't hold to the idea that the salmon's early life is the most important factor in determining its overall survival, unlike other well-known DFO scientists, such as Dick Beamish and the late Bill Ricker, Canada's pioneer salmon scientist who developed the Ricker Curve used to estimate fish populations. -B. R.

The following links were mentioned in this story:

Report on 2008 Ocean Conditions

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