They're like pirates of sorts, but very, very large ones. Alaskan fishermen say they’re increasingly missing out on scores of fish they rely on to make a living because killer whales are making off with their catch.

A few years ago, orca sightings in the Bering Sea were rare, fishermen tell the Alaska Dispatch News. Now the whales are appearing in large numbers to clear fishermen's hooks and lines of cod and halibut.

"It's gotten completely out of control," says Jay Hebert, who’s spent four decades fishing in the Bering Sea. Not only are the whales undeterred by sonar meant to keep them away, Hebert says, but more whales are appearing with increased aggression.

Some fishermen believe the orcas target specific boats, which they follow for days. That comes as no surprise to NOAA biologist John Moran, who says orcas are adept at hunting, can recognize boats by the sound they make, and may also recognize the sound of a hydraulic system lowering fishing gear as a kind of dinner bell.

Moran adds orcas are known to pass on the skills they acquire, which explains why juvenile whales have been spotted around fishing boats. The National Post notes that orcas have been known to adapt their hunting strategies to particular regions within their "remarkably complex social structures." Fisherman have reported losses of up to 30,000 pounds of fish per day, plus the cost of fuel used trying to escape the hungry pods.

(An orca hunting frenzy was caught on film.)

This article originally appeared on Newser: Wily Orcas Are Tormenting Alaska Fishermen