Wednesday, July 18, 2012

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 Alaska.

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.

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