Fishermen in Alaska have their guard up for gangs of unruly marauders hell-bent on stealing their catch. But unlike in tales of old, the pirates in this story lurk beneath the waves.

In rich Alaskan waters, orcas are learning to steal from their human neighbours, and the resulting conflict could have unforeseen consequences for the cetacean predators. A report in Alaska Dispatch News (ADN) describes fishermen exhausting their fuel supplies outrunning the whales, thousands of tons of fish disappearing from hooks and orca pods targeting specific boats.

Just last week, Sitka local Victor Littlefield and his son were out for a day of salmon fishing near southeastern Alaska's Little Biorka Island when an orca rammed their vessel and swam off with the anchor chain. 

"I was prepared for bears, injury and storm, but not prepared for that," Littlefield told the Sitka Sentinel. "I had no idea what to do. You just don't plan on killer whales attacking a boat."

Exactly what the anchor-abducting individual was after is up for debate, but the encounter fits a trend of increasingly bold behaviour in local killer whales. Other captains in the Bering Sea report being tracked over dozens of miles, and even being chased out of the area entirely. 

"It's gotten completely out of control," longliner Jay Hebert, who has fished region for nearly 40 years, told ADN.

A fishermen-targeting squadron of killer whales sounds far-fetched, but orca expert and marine mammal biologist Dr Naomi Rose explains this battle has been brewing for some time – and it's a sign of conflict that could have lasting effects on local wildlife.

"Fisheries are in competition with these highly intelligent predators for the same resources," she says. "That's it in a nutshell. Once the whales figure out they can get the fish for little effort, that's where they will go for a meal."

Adult orcas need to eat some 200,000 calories per day to survive, and these brilliant hunters employ an arsenal of crafty tricks to get that nutrition. Shark-eating killer whales funnel prey towards the surface, ray-eaters team up in hunting pairs, and orcas with a taste for mammals ram, drown or punt their targets.

One thing these tactics have in common, however, is that they all use up precious energy, so it's no surprise that Alaska's orca pods are capitalising on the fishermen's food-finding efforts. "You can't blame them for taking advantage of this easy-to-access resource!" says Rose.

The behaviour isn't unique to Alaska: fishing vessels in South Africa, for example, experience similar "depredations", the term used by scientists and wildlife managers to describe such "stealing" scenarios. Orcas in the area have been known to pluck organ hors d'oeuvres from the bodies of sharks caught on longlines, as well as brains from hooked billfish. Over in Hawaii, false killer whales regularly "tax" the bounty of tuna fishermen: 

It might not look like much, but by the time this animal came into focus, it had already removed three baitfish from their hooks.

Meanwhile, an ongoing tug-of-war has been playing out between sperm whales and the sable fishery for decades. "It's been difficult to resolve," explains Rose. "Whales are so smart, you see – pretty much anything the fishing fleet or managers do to try to restrict their depredations fails."

Many fisheries use acoustic deterrents (think underwater air horns) to prevent non-target species from coming too close, but in Alaska, that tactic seems to be backfiring. Washington resident Paul Clampitt, co-owner of the F/V Augustinetold ADN that orcas in the Bering Sea seem to be growing accustomed to the blaring sounds – even attracted to them. Essentially, the deterrents have become dinner bells for hungry predators. 

Scientists have observed this before in other species, including sea lions and their pinniped kin, as well as other cetaceans. "It's an unintended consequence if ever there was one!" says Rose.

She adds that repeated exposure to acoustic deterrents has the potential to damage whales' hearing. "Whales will persist in taking the fish off the lines, even at the risk of such damage, because the reward is so great," she says. It's possible, then, that such hearing loss partly explains what appears to be the orcas' increasing tolerance of these loud sounds.

Acoustic deterrents aside, the animals can also associate easy pickings with the noise produced by engines and gear alone. NOAA biologist John Moran notes that orcas can use sound to distinguish types of boat, and also recognise specific pieces of equipment, like the hydraulic arms used to lower nets and lines into the water. 

A sperm whale grabs the longline in an attempt to remove sablefish in the Gulf of Alaska

Thieving tendencies can be problematic for marine life in other ways, too. The allure of an easy meal can disrupt normal foraging patterns – and in some cases, young animals never learn to hunt properly. We've seen examples of this in bottlenose dolphins that beg food from tourists.

What's more, fishermen are forced to set additional gear to make up for catch lost to whales, which can ramp up fuel and crew costs by a whopping 80 percent. It also exacerbates fishing impacts.

"It makes [whales] the enemy of a powerful economic sector and puts a bull's-eye on their fins," says Rose. "That's a fight the orcas aren't going to win, in the end. For the whales, it's life or death. For people, it's economic – not precisely the same stakes, really, although of course people need to make a decent living. Still – if fishermen couldn't fish, they would eventually do something else. If whales can't fish … they die."

Unlike the monochrome killer whales, these problems are far from black and white. Alaska's North Pacific Fisheries Management Council plans to expand studies on orca depredations over the coming months, and a recently passed motion will allow officials to look at using crab pot-like fishing gear – which is less accessible to whales – to catch halibut.

Researchers elsewhere in the world are focusing on the secrets of sound – but instead of deterrents, they're looking instead at the noises made by the whales themselves. Echolocation produces specific vibrations on fishing line, and by better understanding it, we might find a way for fishermen to detect how many individuals – and of which species – are nearby, before they deploy any gear. 

This kind of research, however, can quickly get expensive. Like so many other conservation issues, finding solutions will come down to adequate resources.

"It's possible there are innovative ideas still to come for either mitigating the interactions as they currently exist or for new types of fishing gear," says Rose. "Perhaps these interactions aren't unavoidable – but so far innovative approaches have yet to bear fruit."



Top header image: jellybeanz/Flickr