A federal judicial inquiry that is trying to find out why sockeye salmon in the Fraser River are in decline has been told that whatever is killing them, it is not one of the usual suspects.
While mining, logging, hydro projects and other industrial developments in the watershed are degrading habitat quality, none of them can be blamed for the precipitous drop in sockeye stocks, states a science report done for the Cohen Commission of Inquiry Into the Decline of Sockeye Salmon.
Marc Nelitz, lead author of a study that looked at the impact of a variety of human activities, said while the number of adult sockeye has dropped dramatically over two decades, the survival of juvenile salmon has remained stable.
"The collection of all that evidence leads us to conclude it's unlikely the freshwater environment is playing a role," Mr. Nelitz said Thursday, testifying to the Cohen commission.
The report did not reach a definitive conclusion, but Mr. Nelitz said "the weight of evidence" clearly indicates whatever is killing the fish is doing so outside the Fraser environment.
"Based on the evidence it seems most likely that changes in the physical and biological conditions in the Strait of Georgia have led to an increase in mortality during marine life stages," the report states. "Specific mortality agents include lack of food, freshwater and marine pathogens, harmful algal blooms and other factors."
The report did say it is possible "a non-lethal stressor in the freshwater environment is causing mortality during a later life stage," but if so, it wasn't identified.
Mr. Nelitz, a systems ecologist with the environmental consulting firm ESSA Technologies, said the research team looked at the impact of forest harvesting activities, the effect of a massive pine beetle infestation that has altered hydrology by killing off vast tracts of forest, the storage of log booms in the estuary, large- and small-scale hydro projects, urbanization, agricultural development and water use.
It has long been known those activities degrade fish habitat to varying degrees - but the relatively steady survival rate of young salmon in the Fraser eliminates them all as suspects in the mystery the Cohen commission is trying to unravel.
Bruce Cohen, a British Columbia Supreme Court justice, was appointed by Prime Minister Stephen Harper after only about one million sockeye returned to the Fraser in 2009, when more than 10 million fish had been expected. That marked the low point in 20 years of decline, although there was a dramatic and unexpected rebound last year, when more than 28 million sockeye returned, providing the biggest run since 1913.
The Cohen commission, which has ordered a dozen scientific reports and is holding evidentiary hearings in Vancouver, is trying to figure out why sockeye stocks are so unstable, and why they have been declining for so long.
Mr. Nelitz said the study did not look at the cumulative impact of activities along the Fraser, nor did it examine saltwater habitat. Those issues are under separate study.
The report said more information is needed on the early life stages of salmon, and it called for better estimates of juvenile abundance, for more information on the survival rates of young salmon over winter, and for studies on the period when smolts migrate down the Fraser and go out to sea.