Researchers Find Decreasing Trends in Salmon Spawning

A new study of productivity of 64 sockeye salmon populations
concludes that the number of adult sockeye salmon produced per spawner has been
decreasing over the last decade or more along the West Coast of North America.

The report by Randall Peterman and Brigitte Dorner was published
recently in the Canadian Journal of Fisheries and Aquatic Sciences. It says that
this widespread decrease in productivity, from Washington state north through British
Columbia and Southeast Alaska, has important implications for management of salmon
stocks and requires research into its potential causes to help determine future
management strategies.
Peterman is a professor and Canada research chair in fisheries
risk assessment and management at Simon Fraser University’s School of Resource and
Environmental Management, in Burnaby, British Columbia.
He noted in an email response to a query on the study that biologists
in several fisheries management agencies, including the Alaska Department of Fish
and Game, provided data to the researchers.
Peterman said it is possible that the downward trends in productivity
across the sockeye stocks south of central Alaska are the result of a variety of
causes, such as freshwater habitat degradation or contaminants, that have each independently
affected many small regions. Still, he said the large spatial extent of similar
time trends in productivity for over 25 stocks has occurred in both relatively pristine
and heavily disturbed habitats.
This, he said, suggests that shared mechanisms are a more likely
explanation, such as high mortality owing to predators, pathogens or poor food supply
across Washington, British Columbia, Southeast Alaska and the Yakutat region of
Peterson and Dorner analyzed productivity in 64 sockeye salmon
populations. They found that the decline in productivity of Fraser River sockeye
salmon in British Columbia was not unique to that river system, and that productivity
has also declined rapidly in many other populations since the 1990s.
The authors also found that the region with downward trends in
productivity has spread further north over the past two decade, an observation they
said is consistent with large-scale changes in climate-driver oceanographic patterns
that were previously implicated as drivers of sockeye productivity.
The study, “A widespread decrease in productivity of sockeye
salmon populations in western North America,” appears in the August issue of Canadian Journal of Fisheries and Aquatic Sciences.