Radio Script
1999

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New Breakthroughs Hold Promise for Improving Predictions of Alaska Salmon Returns
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STORY: Alaska's salmon have been managed successfully because they are harvested based on the number of fish that return to rivers, estuaries, or lakes to spawn. When fewer come home, fishing is cut back, and vice versa. But predicting returns one year to the next involves a lot of guesswork, and sometimes those guesses are well off the mark. When predictions are too high, it causes economic pain to fishermen and processors who prepare for each season based on predicted returns. When predictions are too low, fishermen and processors have problems taking advantage of the overabundance, such as in this year's Bristol Bay sockeye fishery.

Developing a numerical model that will help accurately predict the survival of salmon was the primary goal of the Sound Ecosystem Assessment project. Everything from life cycle information to predation, water temperature, and currents was investigated in developing a model.

Local salmon hatcheries provided a good test for the prediction formula because salmon released by the hatcheries that survive their time at sea return to hatcheries, allowing scientists to accurately monitor the survival rate of each year's production.

Precise numbers of salmon fry released by area hatcheries were entered into the model. Prince William Sound Science Center Director Dr. Gary Thomas says the model's results were then compared to the actual numbers of salmon that returned to the hatchery to spawn.

THOMAS: "...and we got just a fantastic fit between those measurements--which are just perfectly logical, but unfortunately had never been done before--and the survival of these pink salmon."

Thomas says the model may prove to be the first for predicting marine survival of Pacific salmon, a key to addressing the urgent questions regarding carrying capacity and the effects of climate change on salmon. Inputs for the formula were developed using acoustics, to effectively see--like fish do--what's going on underwater. By-products of the research were the discovery of a huge pollock population in the sound, and the finding that pollock and herring congregate separately in large numbers near shore during the winter. The pollock discovery resulted in a new area commercial fishery. And Thomas says the identification of the overwintering locations could change the way humans manage and fish for both species.

THOMAS: "This opens up the window of actually going in and using in-season management practices for marine fish. And if you think of all the classic problems of marine fish--the fishing of multiple species, so you have all the bycatch problems; the fishing of mixed stocks of the same fish; the problems with getting the fisheries oriented along the coastline, where Alaskan communities can get to it; and probably the last but not least is fishing the fish when they are most valuable. By starting to fish, orient the commercial fisheries to these wintertime aggregations, you solve all these problems." [Prince William Sound Science Center Director, Dr. Gary Thomas.]

Herring have always been important to Prince William Sound fishermen, but the fish's population has been depressed since the early 1990s. Thomas says the development of a survival model for herring has lagged because there is no convenient way to test it like the hatcheries provide for the salmon formula. While sound herring numbers have remained low, the science center has watched the sound's pollock population grow from a measured 40 thousand metric tons in 1994 to 100 thousand tons most recently. Thomas speculates that pollock have prospered under the current warmer climate regime, and that the higher-oil-content, easier-to-prey-upon herring have dwindled, leaving dependent predators like marine mammals and sea birds to decline with them.

OUTRO: From the Sea Grant Program at the University of Alaska Fairbanks, this is Arctic Science Journeys. I'm Dan Bross.