The long journey towards finding out why British Columbia's sockeye salmon have suffered a steady decline, culminating in a devastating collapse last year, began Monday as the commissioner of a public inquiry acknowledged the complex task ahead.

Judge Bruce Cohen told a Vancouver courtroom he was well aware of the contentious debate already swirling about just what is killing the fish.

But he said the commission will only find out how to preserve the Fraser River sockeye if all sides are prepared to work together.

"I remain cautiously optimistic that while principled and reasonable people may disagree on the process or the path to achieving a result, that nevertheless with a collaborative effort, answers can be found and recommendations achieved to address the concerns of everyone involved in the process," Cohen said.

Ottawa ordered the inquiry last year after only a tenth of the 10 million sockeye predicted to swim up the Fraser River actually showed up.

The unexpected collapse forced the closure of the commercial fishery for the third, consecutive year and followed decades of diminishing returns that have been blamed on everything from global warming to overfishing to West Coast fish farms.

All of those theories will be explored at hearings that are expected to continue into the spring, likely lasting much longer than initially scheduled. Cohen's final report is officially due in May of next year, but his findings and recommendations will almost certainly be released much later.

The issue has been further complicated by this year's record returns, with 35 million salmon returning to the Fraser -- a stark and unexpected contrast with the previous season.

On Monday, the hearings began with a basic primer on the life cycle of the Fraser River sockeye, which is actually comprised of hundreds of separate stocks that spawn along the watershed.

Three scientists explained the life cycle of the various sockeye stocks, starting their lives in the freshwater lakes connected to the Fraser before migrating out to sea, returning as adults two or three years later to spawn.

Karl English, the former president of LGL Research Associates Ltd., explained the different routes around Vancouver Island the various stocks take when they return to the Fraser.

He described their journey up the river, which for some can stretch more than 1,000 kilometres to their spawning grounds. The fastest sockeye can travel up to 50 kilometres per day, often passing through fast-running channels and dangerous rapids with changing water temperatures.

"Despite all those challenges, these sockeye have an incredible ability to swim upstream at speeds in freshwater equivalent to what they're doing in the ocean," said English.

"Mother nature has some pretty amazing, talented fish"

More than two dozen lawyers representing 21 different groups will be crowded into the courtroom for the hearings, with each able to cross-examine witnesses and eventually make their own submissions to the inquiry.

The hearings will include the results of up to a dozen research projects by leading salmon biologists and aquatic scientists, as well as reviewing decades of studies that have already been conducted into the sockeye.

The commission's lawyers have also received tens of thousands of documents disclosed by the federal government.

Cohen has already held 10 public forums in various locations and visited more than a dozen sites including First Nations communities to observe their fisheries, land- and ocean-based salmon farms, and the spawning grounds themselves.

The B.C. Supreme Court judge has released a 22-page discussion paper outlining the inquiry's broad plan to examine everything from the organizational structure at the federal Fisheries Department to the possible effects of salmon farming.

The commission is expected to release an interim report on Friday, which will primarily review existing research and set the stage for the commission's research going forward. The interim report will not make any findings of fact or recommendations.

Ernie Crey, fisheries adviser to the Sto:lo First Nation, said he's confident the inquiry will produce the answers everyone is looking for.

"I think this justice is impartial as humanly possible -- I think everyone will get a fair audience, the evidence they present will be listened carefully to," Crey said in an interview Friday after the hearings wrapped up for the day.

"What I'm looking for in the end is a final report that tells us the fate of last year's sockeye salmon run. Why did it collapse so dramatically? Because if we fail to identify the cause or causes, chances are it'll be repeated in a future year."