Yukon River smokehouses should be filled this summer with oil-rich strips of king salmon - long used by Alaska Natives as a high-energy food to get through the long Alaska winters. But they're mostly empty. The kings failed to show up, and not just in the Yukon. One Alaska river after another has been closed to king fishing this summer because significant numbers of fish failed to return to spawn. The dismally weak return follows weak runs last summer and poor runs in 2007, which also resulted in emergency fishing closures. "It is going to be a tough winter, no two ways about it," said Leslie Hunter, a 67-year-old store owner and commercial fisherman from the Yup'ik Eskimo village of Marshall in western Alaska. Federal and state fisheries biologists are looking into the mystery. King salmon spend years in the Bering Sea before returning as adults to rivers where they were born to spawn and die. Biologists speculate that the mostly likely cause was a shift in Pacific Ocean currents, but food availability, changing river conditions and predator-prey relationships could be affecting the fish. People living along the Yukon River think they know what is to blame: the pollock fishery. The fishery - America's largest - removes about one million metric tons of pollock each year from the eastern Bering Sea. Its wholesale value is nearly $1 billion. King salmon get caught in the huge pollock trawl nets, and the dead kings are counted and most are thrown back into the ocean. Some are donated to the needy. "We do know for a fact that the pollock fishery is slaughtering wholesale and wiping out the king salmon stocks out there that are coming into all the major tributaries," said Nick Andrew Jr., executive director of the Ohagamuit Traditional Council. "The pollock fishery is taking away our way of living." Since 2000, the incidental number of king salmon caught has skyrocketed, reaching over 120,000 kings in 2007. A substantial portion of those fish were bound for western Alaska rivers. If those fish had lived, an estimated 78,000 adult fish would have returned to rivers from the Pacific Northwest to Western Alaska. Efforts to reduce by-catch are not new. In 2006, by-catch rules were adopted allowing the pollock fleet to move from areas where lots of kings were being inadvertently caught, thereby avoiding large-scale fishing closures. Then, 2007 happened, and it was back to the drawing board. Last April, the North Pacific Fishery Management Council, the organization that manages ocean fish, passed a hard cap on the pollock fishery. Beginning in 2011, the portion of the fleet that participates in the program is allowed 60,000 kings a year. If the cap is reached, the fishery shuts down. Those who don't participate have a lower cap - 47,591 fish. The loss of the kings is devastating village economies. These are the same Yukon River villages where spring floods swept away homes, as well as boats, nets and smokehouses. There's no money to buy anything, Andrew said. "It is crippling the economy in all of the rivers where we depend on commercial fishing for income," he said. By-catch plays a role but is not the only reason for the vanishing kings, said Diana Stram, a fishery-management plan coordinator at the council. Herman Savikko, an Alaska Department of Fish and Game biologist, agreed. He pointed to changing ocean currents, plankton blooms and even the carnivorous nature of salmon. River conditions could be changing, too, he said. A lot isn't known about what happens to king salmon in the ocean, Savikko said. "Once the fish enter the marine environment it just is a big black box," he said. In a good year, Kwik'pak Fisheries L.L.C. in Emmonak on the lower Yukon employs between 200 and 300 people. This summer, only about 30 people have been hired. Kwik'pak is the largest employer in the region. General manager Jack Schultheis said when the king fishery was shut down, the summer chum salmon run was curtailed as well, even though a good number of chums were returning to the river. The lower Yukon villages are economically devastated, he said. Fishermen used to get between $5 million and $10m. from the fishery. Last year, it was $1.1m. That means instead of making between $20,000 and $30,000 in the 1970s, fishermen are making just a few thousand dollars now, and that is in villages where fuel costs $8 a gallon, milk is $15 a gallon and a T-bone steak costs $25, he said. It's hard to see the villages in such economic hardship, but the Yukon should be managed conservatively until the problem of the disappearing kings is better understood, Schultheis said. "For 50 years, it was an extremely stable fishery," he said.