The scientists looked at weather patterns in the North Pacific Basin over the past century. Then they compared them to records of salmon catches from Alaska and the Pacific Coast states. Weather patterns due to El Niño in recent decades was very important. But when the scientists focused on weather records going back to 1900 from the region north of Hawaii in the Pacific Basin, they found something new. The records showed that air pressure at sea level and in sea surface temperature changed in the same way over periods lasting from 10 to 30 years. They called this change the Pacific Decadal Oscillation.
For about the last 20 years, there has been a large pool of cooler-than-average surface water in the central North Pacific Ocean, with a narrow belt of warmer-than-average sea surface temperatures near the west coast of the Americas. These phenomena, the researchers believe, are distinctive features of the positive phase of the PDO.
The scientists also saw that Alaskan salmon harvests are plentiful during the positive PDO and that far fewer fish are caught during the negative phase. But the change is not the same all along the coast. When fish are plentiful in the Gulf of Alaska, they are scarce along the coasts of Washington, Oregon, and California. We don't quite know how all this works, and oceanographers, meteorologists, and fisheries experts, are all working together to learn more. How important are fishing, blocking of salmon rivers by dams, and changes in weather patterns? Maybe you can help.