The shocking collapse of sockeye stocks in the Fraser River in 2009 was not an isolated event, but was part of a long downward trend in salmon productivity spread over a large area, from Alaska to Washington State, a new scientific study concludes.
"This observation that productivity has followed shared trends over a much larger area than just the Fraser River system is a very important new finding," states the report, filed Wednesday with a federal commission investigating the decline of sockeye in the Fraser.
It suggests that whatever devastated the Fraser's sockeye runs -only about one million of an anticipated 10 million fish returned to spawn - has also afflicted many other sockeye populations, from those in Lake Washington, near Seattle, to those in Yakutat, Alaska, more than 2,000 kilometres to the north.
Researchers Randall Peterman and Brigitte Dorner say it is possible "a coincidental combination of processes such as freshwater habitat degradation, contaminants, pathogens, predators, etc.," have coincidentally affected the populations in many rivers at the same time.
But they suggest a more likely explanation is that something that has an impact over a large area of ocean, where correlated sockeye stocks overlap, is the cause.
"Examples of such large-scale phenomena affecting freshwater and/or marine survival of sockeye salmon might include (but are not limited to) increases in predation due to various causes, climate-driven increases in pathogen-induced mortality, or reduced food availability due to oceanographic changes," the researchers state.
Using data that reaches back to the 1950s, the study looked at 64 populations of sockeye in Washington State, B.C., and Alaska. It found almost all of those stocks have been in decline for two decades. Stocks in Alaska's Bristol Bay and in the Harrison River, a tributary of the Fraser, are the only populations that have gone against the downward trend.
Dr. Peterman, a professor and Canada research chair in fisheries risk assessment at Simon Fraser University, and Dr. Dorner, a specialist in salmon ecology and fisheries management with a private firm, Driftwood Cove Designs, were contracted by the commission to examine sockeye productivity in the Fraser River. They weren't tasked with investigating possible causes, but rather were to identify trends or patterns in population changes over time.
The researchers say that whatever is causing sockeye populations to decline afflicts the fish in the postjuvenile stage because productivity remains high in the early stages of life. Fish are surviving from eggs to fry, but appear to be dying in massive numbers after they have turned into smolts and headed out to sea.
The paper is one of 12 scientific research projects contracted by the Cohen Commission of Inquiry into the Decline of Sockeye Salmon in the Fraser River. Among the other subjects under study are diseases and parasites, marine ecology, the impacts of salmon farms and the effects of climate change.
B.C. Supreme Court Justice Bruce Cohen was appointed by Prime Minister Stephen Harper after the collapse of the Fraser's sockeye run in 2009. A final report is due by June 30, 2012.