North Pacific 'overcrowded' with salmon as population soars

October 3, 2010

More pink, chum and sockeye salmon are in the North Pacific than have ever been seen before, around twice as much as in the 1950s, a Canada-U.S. research team says in a just published article on historical trends.

Around 718 million adult salmon returned to their freshwater homes in 2005, the most recent year that figures were available, the research team says. The evidence indicates the ocean is becoming "overcrowded with salmon," said Randall Peterman, the Canada Research Chair in Fisheries Risk Assessment and Management, and a member of the research team.

The research team, however, sees trouble on the horizon.

The robust adult salmon population has been boosted by the annual release of about five billion juvenile salmon from hatcheries, mostly in Japan and Alaska, Prof. Peterman of Simon Fraser University said Sunday in an interview.

Adult hatchery salmon now account for at least 20 per cent of the total adult salmon production and continue to rise. For some salmon, the percentage is significantly higher. In Asia, 76 per cent of all adult chum salmon from 1990 to 2005 came from salmon hatcheries.

Unless international agreements are developed to manage production levels, hatchery fish may dominate the ocean, Prof. Peterman said.

The research offers a startling contrast to recent headlines indicating the disappearance of salmon. A federal commission of inquiry is currently investigating the decline in the salmon population on Canada's West Coast.

Both perspectives are valid, the research study says. Prof. Peterman said the international trend toward increased abundance is not reflected in every region of the North Pacific. Even though the total number of wild pink, chum and sockeye salmon in the North Pacific is at a historic high, the population in areas such as B.C.'s Fraser River remains of concern, he said.

"Indeed, many pink, chum and sockeye salmon are at very low levels and that is true for the Fraser sockeye salmon in particular," he said. "But if you look across the North Pacific, to Asia and other parts of North America, the total salmon abundance is quite high. Conditions have improved for wild salmon to the point we are seeing record numbers of pink salmon. This is something that most people don't recognize," Prof. Peterman said.

He declined to speculate on the significance of the unprecedented high number of salmon - 34 million - that returned to the Fraser River this year. "One year does not make a trend," he said, adding that the health of the Fraser River salmon was a separate issue.

Increased survival rates, possibly as a result of few predators or more food, were major factors in addition to the hatcheries contributing to the increase in populations, Prof. Peterman said. But the research team was concerned about the competition developing between hatchery salmon and wild salmon, he added.

Hatchery salmon will stray into wild streams and interbreed, he said. "It degrades the fitness of the wild population. The wild population has a store of genetic material that enables them to respond to a variety of situations, like climate change."

Although the hatchery fish would likely dominate the wild stock, they may then struggle to survive if conditions change. Hatchery salmon generally are not as successful as wild salmon in responding to fluctuating conditions such as climate change, he said. Hatchery fish may produce offspring that are less able to withstand factors that affect their survival, he said.

Canadian salmon hatcheries are not major suppliers, Prof. Peterman also said. However, the significant release of juveniles from Alaska's hatcheries affects populations outside their borders.

B.C. salmon migrate into the Pacific Ocean and to the Gulf of Alaska. Intermingling with hatchery fish from Japan and Alaska is a big problem. "Unilateral actions by various hatcheries is having detrimental affect on salmon everywhere," he said.

Carla Shore, spokeswoman for the Cohen Commission investigating the decline of the Fraser River salmon, said Sunday the commission was not researching hatcheries as one of the causes for the decline. However, if credible evidence is available, the commission will look into it, she said.

The article is available in the peer reviewed online October edition of Marine and Coastal Fisheries: Dynamic Management and Ecosystem Science.

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