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Fraser River salmon shortage representative of West Coast trend: report

The decrease of spawning success rates in wild sockeye salmon observed in B.C.'s Fraser River is part of a widespread decrease of salmon abundance along the West Coast, according to a report published this morning in the Canadian Journal of Fisheries and Aquatic Sciences.

Randall M. Peterman, one of the authors of the report, said data on 64 groups of sockeye salmon from Washington State, B.C., and southeastern Alaska led authors to conclude that the downward trend in sockeye productivity in the Fraser is not unique to the area.

Productivity is defined as the number of adult salmon produced per spawning salmon. Peterman said the decrease is "much more widespread on the West Coast than anyone anticipated."

According to Peterman, in the region from Washington State up to southeast Alaska, 24 out of 37 populations of salmon showed a decrease in productivity over the last two decades.

Peterman says the causes of the downward trend are still unknown, but that it is unlikely to be due to small-scale disturbances such as habitat destruction since the decrease has happened simultaneously over pristine as well as disturbed habitat.

Possible causes to be researched are disease (both natural and from fish farms), increased predation, and increased competition for a smaller food supply, according to Peterman.

Peterman says one of the most important findings of the report is that region of productivity decline has spread north over time. By comparing data from as far back as 1950 with more recent numbers, the analysis found that over time, many more populations of sockeye farther north have had a consistent downward trend in productivity. The analysis also shows that decreases are generally greater toward the south.

Peterman says this finding is consistent with previous observations that oceanographic conditions are "driven by climate," and that warmer waters tend to be associated with less food for young salmon in the ocean and increasing instances of large predators, both of which could account for the productivity decreases.

Peterman says that now it's up to other researchers to test various ideas and figure out what is causing the decline. Peterman said the tests should look at the patterns presented in his analysis and take into account the geographic extent of the decline in order to understand the causes.

"If the mechanisms are due to things that we can control, such as human induced pathogens from fish farms, or from predators that we might have some control over, then we might have some management strategies addressing those issues," Peterman said. "However, if the conditions are caused by climate driven oceanographic patterns, then we may not be able to do anything."

Peterman said the implications in the latter case would mean "we have to work extra hard" to reduce stresses on salmon caused by harvest rates, change in habitat, water quality, or anything else that could affect survival rates.

Peterman stressed that the success of the analysis was due to researchers in the past who were given the budget to do "diligent monitoring" from 1950 through the 2000s.

"I want to emphasize that the current budget cutting environment that we're in, in government, is not conducive to understanding what the causes are of these changes," he said.

Hanah Redman is completing a practicum at The Tyee.

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