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Seesaw Shift Seen in Salmon Runs in Pacific NW, Alaska

by Associated Press
Seattle Times - January 16, 2003

ANCHORAGE -- As king salmon swarmed into the Columbia River last year, Alaska salmon harvests dropped to their lowest levels in more than a decade.

The two regions are connected through a complex, seesaw relationship, oceanographer Hal Batchelder said this week during a marine-science conference.

In Alaska, the 2002 statewide catch of about 130 million fish was the lowest since the late 1980s. At the same time, the Columbia saw its largest run since 1938, climaxing a four-year surge in returning fish. The Gulf of Alaska and the Columbia River are connected across 1,000 miles of ocean in a relationship that hinges on vast cycles of currents, temperatures, winds, storms, melting snow, river runoff and the saltiness of the sea.

The seesawing effect in salmon populations may have resulted from the cooling in the Northeast Pacific in the late 1990s, possibly triggering a shift in which animals thrive and which don't, Batchelder said. A warming trend in the late 1970s had the opposite effect. Alaska salmon runs shot up and Pacific Northwest returns crashed. The nature of marine life throughout the region changed.

But figuring out what triggered the shift, possibly part of a 100-year cycle, is more difficult. The details are complex, but speakers kept emphasizing how the Gulf of Alaska, with its location and huge inflow of fresh water, is especially sensitive to climate shifts.

At the conference, University of Alaska Fairbanks scientist Thomas Weingartner talked about how the spinning of the Aleutian-low storm system helps create upwelling of cold, salty water. That nutrient-rich water is necessary to trigger the annual blooms of plankton and tiny sea life during spring's sunny days.

Biologist Suzanne Strom of Western Washington University described how that plankton bloom occurs only when the right conditions converge just the right mixing of the ocean's layers, just the right amount of sunlight. Those tiny animals and plants then form the basis of a complex food web that feeds juvenile fish like pink salmon.

Ted Cooney, a University of Alaska Fairbanks researcher who studied the ecosystem of Prince William Sound, explained how researchers gradually came to a more sophisticated understanding of the relationship between pink salmon and plankton in the past 25 years. Predators play a big role.

Scientists once thought salmon thrived when they found enough food. But pollock and herring, trying to eat the same food, can turn on the young salmon and eat them up. In the end, no simple mechanism controlled salmon survival in Prince William Sound.

The five-day Science in the Northeast Pacific symposium was organized by the Exxon Valdez Oil Spill Trustees Council staff.

Associated Press
Seesaw Shift Seen in Salmon Runs in Pacific NW, Alaska
Seattle Times, January 16, 2003

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