July 12, 2012 | Vol. 39, No. 28

Study attempts to explain low salmon numbers

The amount of mature sockeye salmon present in the waters of Southeast Alaska and other areas of the Pacific Northwest has been on a downward spiral recently according to a study published last week in the Canadian Journal of Fisheries and Aquatic Sciences.

The study states that the, “widespread decrease in productivity has important implications for management of salmon stocks and requires research into its potential causes to help determine future management strategies.”

Dr. Randall Peterman, a professor in fishery science and management at Simon Fraser University in British Columbia, said there could be many reasons for the tremendous decline in salmon available to both commercial and subsistence fishermen.

“It is possible that the downward trends in productivity across the sockeye stocks south of central Alaska result from a variety of causes, such as freshwater habitat degradation or contaminants that have each independently affected many small regions,” Peterman said. “However, the large spatial extent of similar time trends in productivity for over 25 stocks has occurred in both relatively pristine and heavily disturbed habitats.”

Peterman added that other, shared causes are more likely to explain why the low numbers of salmon have become so prevalent.

“Shared mechanisms are a more likely explanation, for example, high mortality owing to predators, pathogens, or poor food supply that occurs across Washington, B.C., Southeast Alaska, and the Yakutat region of Alaska,” he said.

Sixty-four sockeye salmon populations were analyzed in the study and found that productivity has also declined rapidly in many other populations since the 1990s.

Other regions in area – especially Southeast Alaska – have shown downward trends in productivity, which has spread further north over the past two decades.

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