The El Nino of the North and Salmon

Like most creatures, salmon are a tough lot to predict. Some years, so many salmon return to a hatchery that fisheries managers give them away in parking lots. Other years, fishing boats are halted at the docks because biologists find too few fish in the ocean to support an opening.

Though predicting salmon runs is harder than predicting the weather, researchers have noticed a trend: when Alaska wins, the Pacific Northwest loses. Some biologists and oceanographers think they might know why.

Flipping through old issues of fishing journals, Steven Hare of the International Pacific Halibut Commission was struck by the correlations he saw between Alaska and Pacific Northwest fisheries. In 1915, a reporter in Pacific Fisherman wrote that Bristol Bay salmon packers returned to port early due to a lack of fish. At the same time, the chinook salmon run up the Columbia River that borders Oregon and Washington was the best in 25 years. In 1939, the Bristol Bay salmon run was touted as "the greatest in history," while the chinook catch down south was "one of the lowest in the history of the Columbia."

The salmon disparity occurred again in 1972, then most recently in 1994, when Alaska fisherman broke a record for salmon harvest while Washington and Oregon managers were forced to close the chinook fishery on the Columbia because so few fish were returning. The current woes of Pacific Northwest salmon fishermen are not due to salmon's preference for a northern life; Alaska and Pacific Northwest salmon rarely mingle, and many are of different species. So why the correlation between good years here, bad years there?

Ocean conditions must affect the fish. That's the theory of Hare and Nathan Mantua, an atmospheric scientist at the University of Washington. Simply put, the Gulf of Alaska and Bristol Bay since 1977 have been better places for salmon to be than the northern Pacific off the coast of California, Washington and Oregon. In the twenty years before 1977, years when Alaska's fisheries were struggling, the northern Pacific were the better waters for salmon.

The researchers think the pattern has to do with a climate phenomenon similar to El Nino. Instead of El Nino's recurrence pattern once every two to five years, the one that may affect salmon has phases that last 20 to 30 years. This Pacific Decadal Oscillation, as the researchers call it, has its strongest effect in the North Pacific Ocean, while El Nino's more widespread effects originate closer to the equator.

The Pacific Decadal Oscillation may be controlled by the position of the Aleutian Low, a major feature of the North Pacific climate centered just offshore of the Alaska Peninsula. The intensity of the Aleutian Low affects the mixing characteristics in the upper ocean, which in turn affect the creatures salmon feed upon. When the Pacific Decadal Oscillation favors Alaska salmon, waters in the north are a bit different than waters off the West Coast of the Lower 48. The northern ocean's salinity, density, and temperature allows phytoplankton, tiny creatures that depend on light, to thrive, as do the zooplankton that eat them and the salmon that eat the zooplankton.

Researchers call the climate pattern an oscillation because it flips back and forth; Alaska salmon may benefit for 20 to 30 years, but then the Pacific Northwest will be the better place for salmon. Though researchers cannot predict when the pattern will next oscillate--meaning good times for Pacific Northwest fishermen and lighter nets for Alaskans--they feel there is definitely something significant in the Pacific Decadal Oscillation, the El Nino of the North.

For the next week, I will visit the flourishing salmon, zooplankton and phytoplankton of the Gulf of Alaska. Tom Weingartner, an oceanographer with the Institute of Marine Science of the University of Alaska, has invited me on board the R/V Alpha Helix. After setting sail from Seward, I will follow scientists around with my notebook. Hopefully, I'll spend a very small amount of time hanging over the railing of the Alpha Helix, then return to dry land with a few columns.