FAIRBANKS, Alaska -- For two straight years, returns of sockeye salmon to Bristol Bay, the world's largest wild red salmon fishery, have been below state forecasts. Salmon returns to the Kenai Peninsula, the Yukon- Kuskokwim River, and elsewhere in Alaska also have fallen short of expectations.
The declines come as a shock to fishermen and policy makers, but not to some scientists who study the North Pacific Ocean. Their studies of year-to-year and long-term changes in the ocean suggest the salmon declines are, in part, the result of natural ocean cycles.
"It was bound to happen," says Milo Adkison, an assistant professor of fisheries at the University of Alaska Fairbanks School of Fisheries and Ocean Sciences. "You get large year-to-year variations and you also get shifts in salmon abundance that can run for a couple of decades. Salmon productivity itself is connected to conditions in the ocean that operate on similar time scales.
Adkison says research being done at the University of Alaska Fairbanks suggests the changes in fish and shellfish abundance, called regime shifts, occur about every 20 years. It's been about that long since Alaska's salmon stocks rebounded from historic lows. Adkison says a regime shift might be underway, but it's still too early to tell.
"Because there is such a large inter-annual variability, you have a hard time knowing that you're in a new regime until you've seen five years of bad returns in a row or five years of good returns in a row," says Adkison.
UAF assistant professor of oceanography Tom Weingartner also isn't ready to say a regime shift is underway, but he has noticed dramatic changes in the ocean.
"Certainly over the last year we have been influenced by El Nine," says Weingartner. "Whether or not that is occurring in conjunction with a regime shift, I don't know. Our Canadian colleagues noticed in the Gulf of Alaska that nutrients necessary for phytoplankton production were depleted from the surface layer of the ocean. That has not been observed before in the Gulf of Alaska. Another thing that has been noticed is a change in the phytoplankton species composition in the Bering Sea."
Don Schell, the director of UAF's Institute of Marine Science, has been studying bowhead whales to determine how plankton productivity in the ocean is changing. Bowhead whales eat millions of tons of plankton every year, the energy from which is converted to carbon in the whale's baleen. His measurements of plankton carbon in whale baleen indicates that plankton abundance in the Bering Sea has declined significantly during the last 5 years.
"The implication is that the Bering Sea has decreased in productivity by 35 to 40 percent since its peak in 1965 or so," says Schell. "Now a 40 percent decline in the carrying capacity of the ecosystem is going to have profound effects on the top consumers, and I think that is in part what we are seeing now. It implies that there is a bottom-up change occurring."
While scientists know much about changing ocean conditions, predicting such changes far enough in advance to help improve salmon forecasts is still years away. But it is one goal scientists are working toward. Fisheries scientists and oceanographers from throughout the Pacific Rim will meet September 30 to October 3 in Anchorage to exchange research on how to use ecosystem data to better manage fisheries. The conference, Ecosystem Considerations in Fisheries Management, is part of the Lowell Wakefield Fisheries Symposium series sponsored by the Alaska Sea Grant College Program. Several chapters and divisions of the American Fisheries Society are scheduled to hold joint meetings with the ecosystem symposium.
To learn even more about what scientists say about this year's salmon declines, go online at www.uaf.edu/seagrant and click on "Hot Topics."
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