OTTAWA — Prime Minister Stephen Harper said Thursday the federal government will convene a judicial inquiry to investigate the disappearance of millions of sockeye salmon from B.C.'s Fraser River fishery.

The sockeye salmon migration from the Pacific Ocean to the Fraser hit a record low last summer — the second summer in the last three that that has happened — and that has commercial fishermen and environmental activists worried about the very survival of the species. Officials say more than nine million fish appear to have simply disappeared, prompting the closure of the sockeye salmon fishery to both sport fishermen and commercial fishermen.

"We are very concerned about the low and falling returns of sockeye salmon in British Columbia," Harper said in the House of Commons.

Trade Minister Stockwell Day, who is also the regional minister for B.C., will be in Vancouver Friday to name the judge who will head the inquiry and to announce the inquiry's terms of reference.

The government will ask the inquiry, which will have the legal power to compel witnesses to testify, to begin its work early in the new year and report back to the government by May 2011.

"For weeks, the NDP and B.C. communities, fishers and grassroots activists have been calling on this government to establish a judicial inquiry. My office has been literally flooded with petitions calling on this government to stop its shallow public relations exercise and act. The hard work and activism finally paid off," said Peter Julian, an NDP MP.

The timing of the government's announcement has raised some eyebrows as the Conservatives and NDP are locked in a tough byelection fight in a New Westminster, B.C., riding. The Fraser River is that riding's northern border and the state of the fishery is a hot issue in B.C.'s Lower Mainland. Voters in the riding of New Westminster-Coquitlam, as well as those in two vacant ridings in Quebec and one in Nova Scotia, go to the polls Nov. 9. New Westminster voters will be choosing a successor to NDP MP Dawn Black who quit to successfully run for the B.C. legislature. The Conservatives, though, held the riding before the 2006 general election.

In convening the inquiry, the Conservatives say they are fulfilling a campaign promise made during the 2006 general election while Vancouver-area NDP MPs like Julian say they've been calling for an inquiry for weeks.

Government and industry groups have been mystified by the loss of the salmon. Just 1,723 tonnes of sockeye were harvested this year. In 2000, more than 8,800 tonnes of salmon were harvested.

Meanwhile, the sockeye salmon fishery in Alaska, Japan and Russia is booming.

Fishermen in B.C.'s Lower Mainland have been at a loss to explain the disappearance, suggesting the contributing factors could range from overfishing — aboriginals and Alaskans are often blamed, frequently for no reason — to federal conservation policies, to a natural disaster.

Officials with the federal Department of Fisheries and Oceans have been zeroing in on climate change as a contributing factor, which has warmed up the normally cool Fraser River. Sockeye salmon feed mostly on plankton that thrives in cool waters.

The temperature of the Fraser River in August was 18.8 C, a full 1.1 degrees warmer than the historical average.