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VANCOUVER — Volcanic eruptions, giant squid and sea lice have all been invoked to explain the wild swings in one of Canada's most valuable fisheries.
Now scientists have raised the spectre of a mysterious virus killing huge numbers of Pacific salmon before they reach their spawning grounds.
"The mortality-related signature reflects a viral infection," a team of federal and university researchers reported Thursday in a study into the collapse of British Columbia's famed Fraser River sockeye runs.
The compromised salmon that appeared to have a viral infection at sea — a phenomenon co-author Scott Hinch at the University of British Columbia describes as "dead fish swimming" — were 13.5 times more likely to die before spawning than healthy fish.
The study, published Thursday in the journal Science, does not identify a microbial culprit, but suggests the virus may be associated with leukemia and lymphoma.
"There is no doubt there is some form of pathogen involved," Hinch said.
But he says it's not yet known just what it is, when and where the fish are being infected or how much other factors, such as the remarkable rise in river water temperatures seen in the past decade, are contributing to mortality.
Some observers speculate the possible virus may be linked to fish farms, but others say it could be a natural, but until now unrecognized, threat to Pacific salmon.
"There are so many questions to get to the bottom of this and, unfortunately, so few funds to tackle them," says Hinch, noting the tracking systems used to follow salmon for the study are in a "tenuous" state as they don't have assured long-term funding.
"Management agencies are not stepping up to deal with that, in my view," says Hinch, whose previous work helped document how, in bad years, 40 to 95 per cent of Fraser sockeye died before they had a chance to spawn.
Federal fisheries officials, who are responsible for managing wild salmon that support fisheries worth over $1 billion a year, declined requests for interviews.
Federal scientist Kristina Miller, who was unavailable for interviews before deadline, led the four-year-long study. The sleuthing operation involving 15 researchers who took tissue samples in 2006 of adult salmon, many of them still hundreds of kilometres out at sea, and then tracked the fate of more than 150 fish as they headed for and then up the Fraser.
Ocean-tagged salmon showing the gene signature linked to viral infection were 13.5 times more likely to die before spawning, and river-tagged salmon with the same signature of viral infection were 50 per cent more likely to die before spawning.
The Fraser sockeye runs have been in decline since the early 1990s and in 2009 only about one million salmon returned, instead of the more than 10 million expected, prompting Prime Minister Stephen Harper to appoint an ongoing judicial inquiry into the cause of the collapse.
Then, in a stunning turn in 2010, about 30 million sockeye swam into the Fraser, the biggest run seen in almost 100 years. Some scientists say the boom of 2010 was caused by a volcanic eruption in Alaska in 2008, which fertilized the sea and stimulated growth of plankton the fish feed on.
Despite 2010's record return, the Fraser runs are still widely considered to be in a precarious state due to problems that have been linked to overfishing, mismanagement, the spread of sea lice from fish farms and even a recent migration into B.C. waters of hungry Humboldt squid.
The possible viral infection is a new and worrying twist.
"It's very disconcerting,'' says Brian Riddell, a former top federal fisheries scientist who is now CEO and president of the Pacific Salmon Foundation, a non-profit group working to restore salmon stocks.
He says the possibility that Fraser River sockeye are being infected with a virus associated with leukemia and lymphoma is a "big red flag."
He says a "dedicated research effort" is now needed to identify the possible virus and its source.
"It could be something that has just naturally occurred, but there is no reason to think that it couldn't be something that was brought in," adds Riddell, who says investigators need to look at possible links to B.C.'s aquaculture and salmon-farming operations.
Alexandra Morton, a researcher and environmental activist who has studied salmon for years, agrees, saying "this is huge."
"DFO (Department of Fisheries and Oceans) should be turning every stone," says Morton.
James Winton, chief of the fish health section at the Western Fisheries Research Center in Washington State, says the study shows the power of new genetic tools.
"It is a great example of how these new technologies can find things that we didn't know were there before," says Winton.
He says Miller, who led the new study, is very skilled at using the new techniques, which her team used to compare genetic profiles of fish that survived the trip to spawning ground and those that didn't. Although no single mechanisms appeared to be responsible for all salmon deaths in the river, statistical analysis of data revealed a consistent group of genes that were turned up or down in a high proportion of fish that didn't survive.
The study says many of these genes are involved in biological pathways known to be associated with viral activity.
The viral signature was evident in many of the fish long before they entered the river — some were sampled at sea hundreds of kilometres from the river. It suggests the infection may be related to "dysfunction," which could explain why so many sockeye now enter the Fraser weeks early, when river temperatures are higher than those to which the fish are adapted.
Add it all up and the scientists suggest that the "elevated mortality" they documented "is in response to a virus infecting fish before river entry and that persists to the spawning areas.?"
Winton suspects the virus is natural, but says "somebody ought to look at the fish farms to see if they find this particular virus signature in farmed fish."
But he and the other scientists say there are plenty of other factors at play, including rising water temperatures, changes in the food availability due to the scale of industrial fishing in the ocean, competition and interaction with salmon from Alaska and Japan in the Gulf of Alaska, which may also be carrying and sharing viruses.
"It introduces a whole a bunch of questions about just how extensive this is," Riddell says, "but then (the record salmon run in) 2010 has got to give you some hope."
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http://www.canada.com/health/Dead+fish+swimming+virus+hurting+Pacific+salmon/4104926/story.html#ixzz1AyjIbUvW
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Topic: Genes contribute to sockeye salmon mortality in Fraser River: UBC and DFO study (Read 3750 times)