No single force stands out as the main culprit behind the die-off of millions of Fraser River sockeye salmon in recent years, according to findings tabled at the Cohen Commission.
A new report analyzing cumulative impacts on sockeye suggests the fish most likely died at sea, not in the Fraser itself or one of its tributaries.
It points to ocean conditions and climate change as two “likely” factors that may have contributed to the long-term stock decline, particularly as juvenile sockeye migrate out from the mouth of the river to Queen Charlotte Sound and beyond into the open Pacific.
“It is very likely that poor marine conditions during the coastal migration life stage in 2007 contributed to the poor returns observed in 2009,” the cumulative impacts report says.
It notes water temperatures were much cooler in 2008, and the better conditions for salmon may have been part of the reason for 2010’s surprisingly large run.
Climate change and ocean conditions may also play a role further out at sea, it says.
“Some important predators appear to be increasing in numbers and some prey are decreasing,” it notes, rating that as a “possible” contributor to declines.
The report was prepared by consultants ESSA Technologies Ltd. and lead author David Marmorek testified at the commission earlier this week.
His role was to distill the findings of a dozen other scientific reports conducted for the commission to probe separate potential threats to sockeye.
The report found no conclusion is possible on the impact of pathogens and diseases in the sockeye decline.
It cited widely diverging scientific opinions of the inquiry’s two researchers who studied the possible role of salmon farms.
They found diseases from the farms might play a role but completely disagreed in interpreting the actual evidence.
ESSA’s report did note they agreed sea lice, escaped Atlantic salmon and waste from the farms were all unlikely to play a significant role.
It’s also unlikely, the report found, that Lower Mainland land use or upriver factors ranging from logging and mining to agriculture or hydroelectric projects were primary drivers of the decline.
Similarly, pre-spawn mortality of returning sockeye caused by habitat changes or contaminants were unlikely factors.
There are plenty of unanswered questions that were beyond the scope of the commission’s technical reports and therefore weren’t considered by their teams of researchers, Marmorek noted.
Large releases of hatchery fish may compete with salmon for food or attract predators to the same area, he suggests.
That may also be a factor with pink salmon.
The report notes there’s evidence pink salmon from Alaska and Russia compete alongside Fraser sockeye in the North Pacific and could cause food shortages that hurt sockeye numbers in years with large numbers of pinks.
It also raises the question of whether the 2008 eruption of an Alaskan volcano naturally fertilized the ocean with ash and boosted food supplies, leading to the supercharged return of 30 million sockeye in 2010.
Marmorek calls for more research on various salmon stressors, particularly in the early ocean stage.
The Cohen inquiry is in its final days of hearings, with senior officials now taking the stand from the Department of Fisheries and Oceans.
A final report is due next year.
The judicial inquiry led by retired Judge Bruce Cohen was called by the federal government after less than 1.5 million sockeye returned in 2009, far fewer than the more than 10 million expected.