The short-lived invasion of the salmon snatchers

It sounds like a dodgy premise for a B movie: An invasion of fierce, cannibalistic predators from the deep.

But when fisheries biologist Laurie Weitkamp explained the very real threat posed by an unprecedented Humboldt squid migration into northern waters, she had scientists with the Pacific Salmon Commission on the edges of their seats.

This summer, those same scientists were scratching their heads about the record high return of sockeye salmon on the Fraser River.

Now, the mystery deepens: It seems the Humboldt squid, the locusts of the ocean, have vanished from the Pacific north of California this year.

Ms. Weitkamp, of the Northwest Fisheries Science Centre in Oregon, first encountered Humboldt squid by chance one night off the Oregon coast seven years ago.

Crew members called her up on deck to see something odd: Huge numbers of sardines were churning the dark water. Then they saw what was causing the panic. "We were watching these five-foot squid coming up out of the depths, tentacles first, grabbing fish and then disappearing again."

For the scientists on board, it was thrilling to meet a real-life Kraken mythical monster. At the time, the Humboldt squid were almost unheard-of in such northern waters and she had a front row seat, watching the monsters explode up out of the depths in huge numbers to feed. "It just blew our minds."

Since then, Ms. Weitkamp has come to worry about what this shift might mean for the oceans.

"In some ways it's really scary. It's this huge biomass. They had one [test net]last year off the mouth of the Columbia River and they caught 40,000 pounds of squid in a single tow of the net."

Last year saw a population explosion; squid were washing up on the beaches of Tofino on Vancouver Island. The tropical cephalopods were turning up in commercial fishing nets in Alaska.

But this year, researchers have been searching for them - in vain. "This year is really weird. We haven't seen them at all. Zero," she said.

Bill Patton, a salmon biologist for the South Puget Sound, was in the room when Ms. Weitkamp made her presentation to the Pacific Salmon Commission in Portland last February. The scientists in the room had no doubt heard anecdotal reports about the squid migration.

"Everyone was taken aback. I'm sure fishermen would be just panicking," he said. "It's just another of many things that make us anxious about marine survival of salmon."

Her work has been rippling through the research community. Now the Cohen commission, the Canadian judicial inquiry into the 2009 collapse of the Sockeye salmon run on the Fraser River - is asking if the squids' unwelcome presence in northern Pacific waters may have played a part.

Buried beneath the debate over salmon farming, the Cohen commission has listed the Humboldt squid as a potential marine predator of the Fraser River sockeye.

John Payne, staff scientist for Pacific Ocean Shelf Tracking project, was part of a team that tagged two dozen Humboldt squid last year. He has a scar on his hand to remember their "monstrous" sharp beaks.

This year, the hunt for specimens has been difficult.

"Their behaviour is unusual. We don't really know what's going on. That's the mystery and that's why we are tracking them."

Earlier this year, fishery biologist John Field of the National Oceanic and Atmospheric Administration in Santa Cruz, Calif., confirmed for the first time that the Humboldt squid have developed a taste for salmon - with the discovery of otoliths, the ear bones of salmon, in their stomachs.

The Humboldt squid, which can grow to two metres in just two years, are opportunistic feeders: They'll eat each other and have been found with seabird feathers in their stomachs.

However. the Humboldt squid prefer smaller prey than a full-grown salmon. While they are feeding on juvenile salmon, he believes the more significant link between the squid and salmon populations may be ocean conditions.

Warming oceans have allowed the Humboldt to move north, but this year, temperatures in the Pacific have dropped, with lots of cold, subarctic water that is probably very high in oxygen, he said. Better for salmon, less appealing for the squid.

Confirming that link may help salmon researchers better understand the wild swings in salmon stocks - and the future of what was once both a profitable industry and a reliable food source.

Ms. Weitkamp expects her chance to study the squid isn't over. "Squid in general are designed to take advantage of temporary environmental conditions. And these Humboldt squid are the specialists. … I can only imagine they'll be back."