VANCOUVER, British Columbia (AP) _ More than 2 million salmon are swimming in circles off the south British Columbia coast instead of heading home to their fresh-water spawning grounds, and fisheries officials are mystified.

Biologists say such a migratory delay has not occurred in the 70 years that records have been kept on salmon runs, and that future stocks of the internationally prized food fish could be affected.

Factors that biologists speculate could be involved include planetary climatic patterns, changes in the temperature of the North Pacific and a drought that for three years has reduced the snowcap on British Columbia's mountains and lowered river levels along the coast.

''The fish are reacting to something that is happening out in the ocean,'' Canadian fisheries official Fred Fraser said Thursday. ''We see changes in surface temperatures ... and they're getting pushed around all over the place. We really don't have a good handle on it.''

''The bottom line is we still don't know a lot about these things,'' said Pat Chamut, fisheries and oceans' director for the British Columbia region.

What is known is that almost 2 1/2 million pink and sockeye salmon that were supposed to have headed up the Fraser River to their home spawning streams three weeks ago have not.

Also failing to follow migratory schedules are about 100,000 large chinook salmon and another 100,000 coho, a comparatively small salmon.

Fisheries' forecasters estimated about 6 million sockeye would head home this year. Instead, more than 7 million of the red-fleshed salmon showed up.

Predictions that 700,000 chum salmon would begin arriving at the mouth of the Fraser by about Oct. 20 have been scrapped because of bizarre behavior of the other species.

At the mouth of the Fraser, where a mass of pink and sockeye are circling, every so often a few thousand of them spin away in a coil and head into the lower reaches of the river. They arrive a few days later at Hell's Gate, a narrow passage 90 miles inland where water rushes past at up to 25 mph.

So far, the salmon are getting through at a rate, sometimes exceeding 60,000 fish a day, that is sufficient to ensure a successful spawning season. Anxious fisheries officials say they that if the salmon run into more delays, they are considering airlifting them over difficult areas with helicopters.

Early Friday morning, fisheries' engineer Per Saxvik began an experiment involving a series of halogen lights strung along a difficult spot on the river to fool the fish into continuing their battle against the fierce current 24 hours a day.

Salmon do not run against rapids at night, unless there is a full moon.