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Huge sockeye run a mystery, not a trend, scientists say
Panel calls return a blip, recommends large multidisciplinary study on fishery
By Randy Shore, Vancouver Sun
September 15, 2010
http://www.vancouversun.com/technology/Huge+sockeye+mystery+trend+scientists/3526918/story.html
Scientists studying a 20-year decline in the Fraser River sockeye run say this year's miraculous abundance of fish is likely a blip and not a sign the fishery's problems are over.
Sockeye face myriad threats during their four-year life cycle, from food shortages, hungry sea lions and toxic algae to viruses, bacteria and sea lice, according to Simon Fraser University Prof. Randall Peterman.
Peterman is chairman of a panel of 11 experts from the U.S. and Canada assembled by the Pacific Salmon Commission to probe the available data on the decline of the Fraser River sockeye. The panel's report was released last week.
For this year's sockeye run, "all the different sources of mortality lined up to be favour-able at every life stage of the fish," Peterman said.
"Predation mortality, pathogens, starvation, all these things seem not to have been very important for the return this year. It was miraculously positive."
During the 1970s and 1980s, for every fish that spawned in the river, about six adult fish would return four years later. In recent years, after 20 years of steady decline, the number of fish returning for each spawner has dropped below one, culminating in 2009 when only 1.5 million sockeye returned despite predictions that 11 million fish would enter the river.
This year, 34 million sockeye returned to the Fraser.
"This year, productivity levels returned to about seven adults per spawner," Peterman said. "That's a dramatic turnaround, but one point does not make a trend."
Peterman noted that salmon biologists are expected to make good predictions on sockeye returns two years after the fish enter the ocean with very little data about what happens once they enter "the blue box," while weather forecasters with weather stations, satellites and thousands of data points at their disposal hesitate to make predictions beyond five days.
"There's lots going on in the ocean -- what you call a black box, I call a proverbial blue box -- that we cannot track," Peterman said.
At a three-day workshop in June, the panellists and 25 other scientists worked through a variety of hypotheses to explain the long-term decline in sockeye returns in the Fraser and identify factors that seem most likely at play.
Two frustrations emerged.
First, the evidence points to a multiplicity of causes, some of which interact with one another. Food shortages or other stressors during the early life stages of the fish in fresh water could make the fish more susceptible to parasites or viruses that kill the fish much later in life. But while 16 of 18 sockeye populations in the Fraser are suffering weak returns, populations for which data exist appear quite robust during freshwater life stages.
Pollutants in the river from human activity might also weaken the fish. Pink salmon, which are running strong in the Fraser, may be eating the juvenile sockeye as they migrate to the ocean. Maybe.
"There are a number of processes interacting, probably in the marine environment, but we're not exactly sure," Peterman said.
The second frustration: There are massive holes in the evidence.
"We cannot distinguish among the possible hypotheses more finely because we don't have the data," he said. "It could be anything from shortages of food, increasing predation by growing populations of marine mammals (Steller sea lions, white-sided dolphins, humpback whales and harbour seals), or increased pathogens that are causing this mortality inside the Strait of Georgia."
The panel has recommended the commission undertake a large-scale multidisciplinary study -- likely to be led by the Department of Fisheries and Oceans -- to collect data on pollutants, pathogens, predation and other known threats to the health of the sockeye at coordinated times and locations to create a comprehensive data net.
Read Randy Shore's blog, the green man, at vancouversun.com/randyshore
rshore@vancouversun.com
Panel calls return a blip, recommends large multidisciplinary study on fishery
By Randy Shore, Vancouver Sun
September 15, 2010
http://www.vancouversun.com/technology/Huge+sockeye+mystery+trend+scientists/3526918/story.html
Scientists studying a 20-year decline in the Fraser River sockeye run say this year's miraculous abundance of fish is likely a blip and not a sign the fishery's problems are over.
Sockeye face myriad threats during their four-year life cycle, from food shortages, hungry sea lions and toxic algae to viruses, bacteria and sea lice, according to Simon Fraser University Prof. Randall Peterman.
Peterman is chairman of a panel of 11 experts from the U.S. and Canada assembled by the Pacific Salmon Commission to probe the available data on the decline of the Fraser River sockeye. The panel's report was released last week.
For this year's sockeye run, "all the different sources of mortality lined up to be favour-able at every life stage of the fish," Peterman said.
"Predation mortality, pathogens, starvation, all these things seem not to have been very important for the return this year. It was miraculously positive."
During the 1970s and 1980s, for every fish that spawned in the river, about six adult fish would return four years later. In recent years, after 20 years of steady decline, the number of fish returning for each spawner has dropped below one, culminating in 2009 when only 1.5 million sockeye returned despite predictions that 11 million fish would enter the river.
This year, 34 million sockeye returned to the Fraser.
"This year, productivity levels returned to about seven adults per spawner," Peterman said. "That's a dramatic turnaround, but one point does not make a trend."
Peterman noted that salmon biologists are expected to make good predictions on sockeye returns two years after the fish enter the ocean with very little data about what happens once they enter "the blue box," while weather forecasters with weather stations, satellites and thousands of data points at their disposal hesitate to make predictions beyond five days.
"There's lots going on in the ocean -- what you call a black box, I call a proverbial blue box -- that we cannot track," Peterman said.
At a three-day workshop in June, the panellists and 25 other scientists worked through a variety of hypotheses to explain the long-term decline in sockeye returns in the Fraser and identify factors that seem most likely at play.
Two frustrations emerged.
First, the evidence points to a multiplicity of causes, some of which interact with one another. Food shortages or other stressors during the early life stages of the fish in fresh water could make the fish more susceptible to parasites or viruses that kill the fish much later in life. But while 16 of 18 sockeye populations in the Fraser are suffering weak returns, populations for which data exist appear quite robust during freshwater life stages.
Pollutants in the river from human activity might also weaken the fish. Pink salmon, which are running strong in the Fraser, may be eating the juvenile sockeye as they migrate to the ocean. Maybe.
"There are a number of processes interacting, probably in the marine environment, but we're not exactly sure," Peterman said.
The second frustration: There are massive holes in the evidence.
"We cannot distinguish among the possible hypotheses more finely because we don't have the data," he said. "It could be anything from shortages of food, increasing predation by growing populations of marine mammals (Steller sea lions, white-sided dolphins, humpback whales and harbour seals), or increased pathogens that are causing this mortality inside the Strait of Georgia."
The panel has recommended the commission undertake a large-scale multidisciplinary study -- likely to be led by the Department of Fisheries and Oceans -- to collect data on pollutants, pathogens, predation and other known threats to the health of the sockeye at coordinated times and locations to create a comprehensive data net.
Read Randy Shore's blog, the green man, at vancouversun.com/randyshore
rshore@vancouversun.com
ollutants in the river from human activity might also weaken the fish. Pink salmon, which are running strong in the Fraser, may be eating the juvenile sockeye as they migrate to the ocean. Maybe.
