CORVALLIS, Ore. - To anyone who has ever felt the slam of a chinook hitting a trolled herring, the words are music to the ears: "ideal ocean conditions for salmon."

Now the question is, how long will these productive conditions last?

Since 1999, the Pacific Ocean off Oregon has cooled and become full of "boreal copepods," more commonly seen off the coast of Alaska and harbingers of productive waters off Oregon. Feeding on these northern zooplankton are herring, anchovies and sardines - all baitfish seen as critical to salmon survival.

Scientists think the ideal ocean conditions are a product of a "climate regime shift" that has seen an intensification and enlargement of the low pressure system off Kodiak Island every winter for more than 20 years suddenly shift westward in 1999. But they aren't sure how long it is going to last.

"What this does is create some real dilemmas for fish assessments," said William Peterson, an oceanographer for the National Oceanic and Atmospheric Administration, and a courtesy professor at Oregon State University. "This is the third year of really good ocean conditions. So, should managers bump up the catch rate of salmon? Of groundfish? Or hold steady? The science just isn't there yet."

Peterson readily admits that scientists have "no idea" how long the climatic conditions resulting in this salmon utopia will last.

"In a sense, we already have been successful because the Pacific Fisheries Management Council and other stock assessment folks now recognize that fish populations are affected by climate, not just the catch rate," Peterson pointed out. "And there are more subtle ties that need to be studied."

Black cod, for example, live at 600-foot depths, but will spawn in the upwelling zone on the continental shelf. Any shift in the upwelling, zooplankton species, or baitfish populations may have an impact on their life cycles.

The biggest impact, however, may be on coho salmon, says NOAA's Richard Brodeur, who also is on the faculty of OSU's College of Oceanic and Atmospheric Sciences and the Department of Fisheries and Wildlife.

"Coho come back to spawn as three-year-olds," Brodeur said. "They go out to the ocean as yearlings in the spring and return the following fall, but the first few months at sea are critical. They really respond to changes in the ocean conditions and the abundance of baitfish improves survival rates.

"Since many of these baitfish produce millions of offspring, all it takes is a 2- or 3-percent change in survival to make a huge difference in their population size," Brodeur said.

Oceanographers from OSU, NOAA, and other institutions will make a series of cruises off the Oregon coast during the next two years to monitor salmon survival rates, zooplankton populations and ocean conditions. Satellite data beamed to OSU's supercomputer network will provide more information.

"To be honest, we don't know what will happen next," Peterson said. "Everyone has theories and some are out there. One model even suggests that this could be a positive offshoot of global warming - that as the land mass warms and creates a deep low pressure, it will interact with the high pressure on the ocean and create more upwelling.

"It will be another 10 years before we know on that one. It's just another idea on the table."