Gillnetters wait for their opening to catch the prized Fraser River sockeye near Steveston, B.C., in August 2006. (Chuck Stoody/Canadian Press)

Scientists and others are scrambling to determine what happened to millions of sockeye salmon that defied their predictions and failed to return to the Fraser River this summer, leading to the closure of all the sockeye fishing on the river for the third year in a row.

After two of the leanest years on record, scientists had predicted a healthy return of sockeye in 2009. But the most recent numbers show this year's Fraser River sockeye run is only expected to be 600,000 fish, about seven per cent of the original prediction of 8.7 million, making it perhaps the worst return on record.

The original prediction was largely based the strong spawning year in 2005 and the salmon's four-year life cycle, but was considered to be accurate only 50 per cent of the time.

Fishermen devastated

Irvin Figg, the president of the United Fisherman and Allied Workers union, said news of the closure is devastating for commercial fishermen, and it has been made worse by news that the other summer big run on the Skeena River on the Central Coast also might not open to commercial fishing this year, hitting many fishermen with a double-whammy.

"It's depression, and a certain amount of anger, and the anger comes from not knowing what the heck is going on. You know, is this the end of an era? I hope not," said Figg.

Figg wants the federal government to pay for more studies to uncover why so few sockeye are returning to their spawning grounds.

In 2008 and 2007, DFO also closed the Fraser River to both commercial and recreational sockeye fishing because of the low returns. To the south, the U.S. also cancelled commercial salmon fishing off the California and Oregon coasts last year.

Ecologist questions causes

Ecologist Craig Orr, who studies sockeye as the executive director of Watershed Watch Salmon Society, said the cause of what is now three years of low returns is unclear.

"Whether it's as juveniles leaving the system, or as adults returning, they are not getting the food in the high seas. Canada needs to get its act together and get some real investigation going on what's happening to these fish," said Orr.

Some experts blame warmer ocean and river temperatures, and declining food supplies in the open oceans for the failing salmon runs.

But warmer water temperatures can't fully explain the demise of so many fish, said Orr, who is calling for a full investigation of the impact of fish farming and sea lice on wild stocks.

Scientists, environmentalists, politicians and fish farmers have been arguing for years about the impact salmon farms are having on young salmon fry, with many opponents of fish farms predicting sea lice from the industrial operations would decimate wild salmon stocks.