Fish counters in green rain slickers patrol a narrow channel of glacier-fed river, keeping close tabs on the thousands of salmon that migrate upstream to spawn.

Elsewhere along the coast, observation teams slosh through waterways in waders, carrying rifles to ward off aggressive bears. Still others monitor the migration from low-flying planes, or take inventory at fish weirs and atop counting towers placed strategically throughout the wilds of Alaska as part of an elaborate surveillance of returning fish.

At the first hint of a decline in salmon numbers, the Alaska Department of Fish and Game is quick to shut down coastal fishing grounds and order fishermen to pull in their nets and lines.

State officials do this without protest from fishermen. Rather, they work together, to protect not just a prized fish, but an economic bonanza and a leading source of private-sector jobs in the state.

"We don't want to catch fish this year, but in future years too," said Juneau fisherman Jev Shelton, who remembers when the collapse of Alaska's salmon fisheries from overfishing was declared a national disaster about 50 years ago.

Threatened with the loss of one of its top industries, Alaska began limiting the number of boats and fishermen, restricting the size of their catches, and giving fishermen a stake in the long-term viability of salmon and other fish.

If only the rest of the world had learned from Alaska's response to the crisis. Today, records show that 90% of the big fish — tuna, cod and swordfish — are gone from the oceans. If the serial depletions continue unabated, a group of scientists recently predicted, major seafood stocks will collapse by 2048.

Alaska's policy shifts are still an exception. By and large, ocean fishing, especially in international waters, remains a free-for-all with too many boats chasing too few fish.

Only about 6% of the global fish catch is certified as "sustainable," meaning that fish are not pulled from the ocean faster than they can reproduce and are not caught in ways that destroy other sea life or undersea habitat. Much of it comes from Alaska.

Though other U.S. regions and nations have been reluctant to rein in their fishing fleets, help has emerged from an unexpected quarter.

Wal-Mart Stores Inc. has pledged within three to five years to sell nothing but wild-caught seafood that meets standards for sustainability set out by the nonprofit Marine Stewardship Council. Founded in 1997, the council grants a blue and white label to fish that stand up to independent certification.

Wal-Mart's shift in policy has rippled through the global seafood trade. The National Fisheries Institute, the seafood industry's principal lobby, has become a booster of the sustainable seafood movement after years of resistance.

McDonald's is now nudging its suppliers to come up with sustainably caught fish for its Filet-O-Fish sandwiches, which consume 110 million pounds of Alaskan pollack, New Zealand hoki and other whitefish from around the globe.

Meanwhile, Darden Restaurants, the parent of Red Lobster, is taking similar steps, as is the Compass Group, America's largest food-service provider to corporate and university cafeterias.

In turn, commercial fisheries are seeking certification, for flounder caught off Japan, herring in the North Sea, Chilean hake and albacore off California.

"This is supply-chain pressure of the best kind," said Rupert Howes, chief executive of the London-based Marine Stewardship Council. "The Wal-Mart commitment is actually catalyzing commitments from other retailers around the world. We have a major Japanese retailer that wants to launch MSC-labeled products."

Yet there could be even more risks for precarious fish stocks as megagrocers such as Wal-Mart enter the seafood market, creating increased demand for the types of fish that the sustainable seafood movement is trying to save.

"That's what fundamentally undermines the market-based approach," said Daniel Pauly, a fisheries scientist at the University of British Columbia. "You create more customers for fish and invariably increase the pressure on the stocks."

Pauly and other critics believe it's too late for the market alone to protect fish when the world's population is growing and two-thirds of the world's commercial stocks are already being fished at or beyond their capacity.