In the Bering Sea, near the edge the continental shelf, fishermen are trying to escape a predator that seems to outwit them at every turn, stripping their fishing lines and lurking behind their vessels.

The predators are pods of killer whales chasing down the halibut and black cod caught by longline fishermen. Fishermen say the whales are becoming a common sight — and problem — in recent years, as they've gone from an occasional pest to apparently targeting the fishermen's lines.

Fishermen say they can harvest 20,000 to 30,000 pounds of halibut in a single day, only to harvest next to nothing the next when a pod of killer whales recognizes their boat. The hooks will be stripped clean, longtime Bering Sea longliner Jay Hebert said in a phone interview this week. Sometimes there will be just halibut "lips" still attached to hooks — if anything at all.

"It's kind of like a primordial struggle," fisherman Buck Laukitis said about the orcas last week. "It comes at a real cost."

The whales seem to be targeting specific boats, fisherman Jeff Kauffman said in a phone interview. FV Oracle Captain Robert Hanson said juvenile whales are starting to show up, and he thinks the mothers are teaching the young to go for the halibut and black cod the fishermen are trying to catch.

Hanson, a fisherman who's worked in the Bering Sea since 1992, said the orca problem has become "systemic" in recent years. There are more pods present, he said, and the animals are getting more aggressive.

In a letter he sent to the North Pacific Fisheries Management Council last month, Hanson described a series of challenges he faced in recent years. On a trip to the continental shelf in April he said his crew was "harassed nonstop." He wrote that they lost approximately 12,000 pounds of sellable halibut to the whales and wasted 4,000 gallons of fuel trying to outrun them.

Another time he drove his boat out to the edge where he's allowed to fish, an isolated area near the Russian border. He fished for a day before a pod of at least 50 whales showed up, he said. He tried to fish, he wrote in the letter, but after two days he just "gave up."

"The pod tracked me 30 miles north of the edge and 35 miles west (while) I drifted for 18 hours up there with no machinery running and they just sat with me," he wrote.

Hebert, captain of the Aleutian Sable, said the orca plundering over the last five years is the worst he's seen in his 39 years of fishing in the Bering Sea.

Hebert said the whales seem to seek out the longliners. He's tried using sonars that emit a frequency designed to keep the whales away, but he said it's not strong enough to deter them. He would like to see pots, instead of hooks, introduced as a method for catching halibut, similar to how black cod were harvested in the Gulf of Alaska as a result of sperm whales targeting longliners.

Hebert, who estimates he's caught millions of pounds of fish in the Bering Sea, said if there are whales he simply doesn't fish anymore. It's not worth it, he said, to work so hard only to have your fishing lines stripped "100 percent."

"It's gotten completely out of control," he said.

Help on the way?

Killer whales targeting fishing vessels happens all over Alaska, including in the western Gulf of Alaska and Aleutian Islands. But it's more common on the Bering Sea's continental shelf, where a higher density of whales overlaps with halibut and black cod fishing grounds.

Studies show that at least 1,475 killer whales use Western Alaska waters.

Japanese fishermen first encountered thieving orcas in the 1950s. But research looking at exactly how much killer whales target Bering Sea fishermen only goes back to 1995, according to National Oceanic and Atmospheric Administration fisheries biologist Dana Hanselman.

A study published by Hanselman this year looked at black cod depredation by whales in Alaska. There was an increase in whales going after the fish between 2000 and 2008, but that has varied in later years, Hanselman said. But the reason for that could be that fishermen aren't targeting the fish as much for fear of whales going after their catch, Hanselman wrote in an email.

Killer whales are skilled hunters, NOAA fisheries biologist John Moran said. He said they can tell the sounds of different boats and even learn the sounds of the hydraulic system that lowers the fishing gear into the water.

"Grabbing a fish off a line is nothing," he said.

They're also highly social animals, he said, making it easy for the whales to quickly learn from others how to go after the fishing boats.

Laukitis, who is also a member of the North Pacific Fisheries Management Council, the regional management group that oversees federal fisheries in Alaska, recently introduced two motions at the council. One would allow the council to research the extent of the problem of killer whale depredation — or the plundering of fishing lines by whales — on halibut and black cod longline fishermen in the Bering Sea. The other would consider whether or not allowing pots to catch halibut would be a better option in keeping the whales away from the catch.

The motions passed unanimously. Laukitis said the council is taking a cautious approach to the issue to figure out the extent of the problem. He said fishing is known for risks, but that the whales present a new, frustrating challenge.