Sunday, August 9, 2009

El Nino Stengthening, Could Mean Changes for Ocean Productivity

Strengthening El Nino conditions in the Pacific likely mean that this winter will be mild and dry compared the norm. El Nino also bring warmer sea surface temperatures to the North Pacific and can result in lower ocean survival for salmon. La Nina conditions, or cool ocean temperatures coupled with good upwelling conditions the last two years have resulted in good survival and growth for outmigrant smolts and promise to bring banner returns of Pinks, Coho and Chinook to the Pacific Northwest over the next couple of seasons. While high returns are always encouraging it is vital that managers and policy makers understand the cyclical nature of salmon returns when considering harvest fisheries or increased hatchery releases. More information in the Columbia Basin Bulletin.

A perfect example of this is on the Oregon Coast where ODFW hopes to open a harvest fishery this fall for ESA listed Coho Salmon. Spawning Coho salmon returning this fall outmigrated during some of the most favorable ocean conditions in a decade and as a consequence the return is predicted to be a few thousand fish above the escapement goal. What will managers say however when the runs again drop to a fraction of the escapement goal in 4 years when ocean conditions are not as good? How will it look to have harvested a stock of listed fish in the one year they actual returned in relative abundace. Keep in mind the escapement goal for Oregon Coastal Coho is probably less than 10% of the historic return.

High escapement years allow fish to colonize new areas which may have long been devoid of fish. In years of high escapement fish with more marginal, or less productive lifehistories, entry timing, and spawning areas return in much higher than normal. Diversity in a salmon population drives abundance over the long term, and protects the population from collapse when environmental conditions change. Present day Coho salmon populations are much less diverse than historic populations and only in recovering that diversity will we be able to recover any semblance of a historic population.

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