The largest return of sockeye salmon in almost a century is expected to swim up British Columbia's Fraser River this year, after an unexplained collapse in 2009 prompted a public inquiry.

The Pacific Salmon Commission, a joint Canadian-U.S. body that helps regulate the West Coast salmon fishery, has increased its stock assessments after recent test catches suggested a larger-than-expected return.

A notice posted to the commission's website Tuesday predicted the total Fraser return this year will be 25 million fish -- the largest since 1913.

The optimistic forecast stands in stark contrast to last year, when the commission predicted 10 million fish would swim up the Fraser and only 1.5 million showed up.

The federal government has ordered a public inquiry into the decline of sockeye runs on the Fraser, which is scheduled to begin evidentiary hearings next month.

Barry Rosenberger of the federal Fisheries Department says the estimate represents a combination of runs along the Fraser.

Salmon spend four years at sea before returning to the river.

"We had 4.7 million spawners around the Fraser River, so that's a fairly good escapement," said Rosenberger. "Clearly, they must have had good marine survival in their fresh-water life stages, so we've got a fairly good return going on from that spawn four years ago."

The federal fisheries minister, Gail Shea, issued a written statement welcoming the news of strong returns, pointing out that commercial, recreational and native fisheries have all been able to open for the first time in four years.

"2010 is turning out to be a banner year for Fraser River sockeye salmon," said Shea. "Several fishery openings for Fraser River sockeye have already occurred in 2010 and more are planned."

It's still not clear why last year's salmon return suffered such a drastic collapse, with theories ranging from water temperature in the Fraser or in the ocean, new predators at sea, changes in the food supply or the environmental impact of fish farms, to name a few.

Former B.C. Supreme Court judge Bruce Cohen has been appointed by the federal government to figure out what caused the collapse.

A discussion paper released in advance of procedural hearings in June said the inquiry will examine everything from fish biology to the organization of the Department of Fisheries and Oceans.

Cohen will have the power to compel testimony and will then make recommendations to Ottawa.