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Cold Ocean Means More Salmon

by Bill Rudolph
Columbia Basin Bulletin, February 7, 2008

Ocean temperatures off the Northwest Coast have remained below normal and may stay that way for the rest of the year, judging from the continued cooling of waters near the equator, the Climate Impacts Group (CIG) from the University of Washington reported last week.

That means La Nina conditions should stick around for some time to come, boosting basic biological productivity in nearby waters, good news for juvenile salmon who will be heading for the ocean in a few months.

(An official La Nina episode is defined as any five-month period when sea-surface temperatures in the middle of the equatorial Pacific remain half a degree C below normal).

The last official La Nina occurred from September 2000 to March 2001. Before that, a stronger La Nina took place between June 1998 and June 2000, coming off a very powerful El Nino that ended officially in March 1998.

By 1999, ocean conditions had improved drastically off the Pacific Coast, with salmon populations increasing in kind, with return rates for many salmon runs improving by an order of magnitude or more.

Lately, coastal sea surface temperatures (SSTs) have been at least 1 degree C below normal along the Washington coast, and at least 2 degrees C below normal along the Oregon and much of the California coast, according to the CIG's latest report.

"This pattern of colder than normal west coast SSTs is consistent with the cold ENSO conditions that have dominated the equatorial Pacific in the last several months," they said.

However, they also said the cooler conditions are slowly heading toward a warmer state, according to the latest numbers that make up the Pacific Decadal Index that tracks long-term warming and cooling trends.

"The existing pattern of colder than normal SSTs along the west coast of North America and on the equator, and warmer than normal SSTs in the central north Pacific is characteristic of the cold polarity of the PDO phenomenon. The amplitude of this pattern in September, October, November, and December was -0.36, -1.45, -1.08, and -0.58, respectively, indicating that the PDO has diminished in strength since October."

But the La Nina that has appeared seems to be stronger than some scientists had anticipated, "with mean October-November-December SSTs 1.48 degree C below the 1971-2000 normal in the Nino 3.4 region (5N-5S, 170-120W), the coldest SSTs at this time of the year since 1988 and the 6th coldest in the 58 year record."

These conditions may stick around for awhile. The NOAA Earth System Research Laboratory experimental SST forecast calls for the PDO pattern to remain negative for the rest of the year.

Nearby ocean temperatures began cooling again in 2006 after two hot years in a row. Canadian researchers measuring SSTs off Vancouver Island found that 2004 and 2005 summer water temperatures were "two of the four warmest in almost 50 years of sampling along this line." But since mid-August of 2006, SSTs have been below normal.

The changes should benefit salmon stocks up and down the West Coast, where it was reported last week that 2007 fall chinook returns (natural and hatchery) to the Sacramento River were near an all-time low. Only 90,000 returned, when the objective was 122,000 to 180,000 fish. About 317,000 natural and hatchery chinook reached the Sacramento in 2006.

The 2007 Sacramento return was the lowest since 1973, and jack counts were only about 10 percent of average, which likely means another extremely poor run for this year.

Some critics blame water diversions in the river for the poor return, but ocean conditions were poor when the fish went to sea in 2005. A lack of tiny shrimp in the waters off San Francisco led to a huge die-off among seabirds in 2005 and 2006.

Fishermens' groups are already talking about getting another relief package from the federal government similar to $64 million in aid that helped out many commercial fishermen and related businesses in California and Oregon after drastic harvest cuts were implemented in 2006 to help the weak chinook run on the Klamath.

But these days the Klamath seems to be doing just fine. About 50,000 wild fall chinook returned to spawn there last fall, twice the number from the previous year, and better than any of the three years before that.

Up the coast, Columbia River fall chinook numbers were down considerably last year from the recent past as well, with fall chinook counts at Bonneville Dam at less than half the 10-year average. Poor ocean conditions in 2004 and 2005 were likely responsible for the downturn.

Jack counts for Bonneville tules took a 40-percent jump in 2007, which should signal a much-improved fall run. Jack counts for the upriver bright run are also better, which has managers expecting an above-average run back to the famous Hanford Reach.

Spring runs in the Columbia are expected to make a huge bounce back from improved ocean conditions, as well. This year's spring chinook run above Bonneville could be way up there--possibly the third highest since 1938, when the dam was completed. In December, Columbia Basin harvest managers released their preliminary number--269,000 springers above Bonneville--three times the size of the 2007 run.

More potentially positive news: one NMFS researcher told NW Fishletter that it's not uncommon for another La Nina to follow a year behind the first one.

Related Sites:
The Pacific Northwest Climate CIGnal

Bill Rudolph
Cold Ocean Means More Salmon
Columbia Basin Bulletin, February 7, 2008

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