Alaskan Sperm Whales Have Learned How to Skim Fishers' Daily Catch

Sperm whale. Whales are related to hoofed animals. Hiroya Minakuchi/Minden/National Geographic Creative

For longline sable fishers in the Gulf of Alaska, there are few omens of doom more chilling than the enormous shadow of a whale approaching their boat. That's because in the past several years, male sperm whales, the lone wolves of the ocean, have been behaving strangely. They have been teaming up to hunt fish right off fishers' hooks, and every year more whales are coming to eat from the fishing line buffet, leading some scientists to speculate that they're somehow communicating about the richness of the hunting ground and sharing tips. They're destroying thousands of dollars' worth of fishing gear, altering the population of sablefish and endangering their own lives with the chance of getting caught in lines.

It all started about 20 years ago, when the sable fishing season was extended from one or two weeks to eight months. Previously, the season was so short that sperm whales swimming in and out of the Gulf of Alaska hunting for food didn't have enough time to learn the habits of the fishers. Back then, depredation, the scientific term for when animals go around plundering food, wasn't a problem. But just five years after the season extension, the whales had become so adept at hunting off the longlines that fishers were starting to panic.

Since then, it's only gotten worse, says Linda Behnken, a 30-year commercial fishing veteran and executive director of the Alaska Longline Fishermen's Association. Today, Behnken and the North Pacific Fishery Management Council estimate that the costs of the damage to vessels targeted by whales, and the extra time and bait that go into attempting to meet fishers' quota after losing their catch, add up to more than $1,000 per ship, per day. "Most fishermen that have experienced whale depredation will tell you that [estimate] is low," she says.

Sablefish—or black cod, as the local fishers call them—typically live 2,400 to 3,600 feet below the surface. To catch them, fishers spend six to 12 hours traveling 15 to 90 miles offshore. Once they arrive, they lay their lines. The longline generally runs about 3 miles, with an anchor on one end to attach it to the seafloor and a buoy on the other so the fishers can find it at the end of the day. Along the line, there will be somewhere between 1,000 and 4,000 hooks, with bait on each one. Boats typically set two lines at a time, which sit for 12 hours. Fishers haul in the lines using hydraulics, and one crew member will typically stand on the boat's rail and pull each fish off the hook as it comes out of the water. When no whales are present, a line with 2,000 hooks on it will typically catch 500 to 1,000 fish.

But when the whales are around, says Behnken, the fishing is miserable. "The catch can be easily one-quarter of what you would expect, and if you have enough whales on you, they can clean you out," says Behnken. "They are usually taking turns going down and getting fish. When you finish hauling, they'll all come up to the surface. Last year, one came right next to the boat and rolled. He was looking right at us. Maybe he was looking to see if there was more coming." On one trip, her boat had as many as six whales surrounding it, waiting for dinner. "You start having lines come up with fish that are bitten in half, and you can see the whale teeth marks."

After years of this, Alaska's fishers reached out to a team of scientists for help. Quickly, a group formed: the Southeast Alaska Sperm Whale Avoidance Project, or SEASWAP, a collaboration among fishers, academic researchers, field scientists and both local and national government agencies. But deterring the sperm whales has proved to be much harder than anyone anticipated.

In part, it's because sperm whales are not well understood, despite being one of the most famous of the ocean's mammalian hunters. Scientists do know they're the largest of the toothed whales and are easy to identify thanks to their giant, square-shaped heads and long, pointed lower jaws. Their blowholes are set at an angle off to the left side of their heads, and they use a series of clicks and echolocation to communicate and identify prey. For the most part, they eat squid (about a ton per day), and some speculate they may even find themselves in regular battles with giant squid, as it's not uncommon for them to be found with large, suction-cup-shaped scars.

But beyond that, we don't know much. Sperm whales are very difficult to study because they dive deeper than any other great whale—more than 5,000 feet—and once they get down there they can stay submerged for up to 50 minutes before they surface for air, miles away from their initial dive spot. So there were really no clues as to how the whales were finding the boats just as the fisherman were reeling in their lines. "Generally, what happens is the guys go out, they set their gear, let it soak for several hours and then pick it up. The whales won't be around until they're hauling the gear back. How do they recognize this thing that's become the dinner bell?" asks Russ Andrews, a marine biologist with SEASWAP.

To answer the question, Aaron Thode, a marine mammal acoustic specialist at the Scripps Institution of Oceanography at the University of California, San Diego, set up passive listening devices on moorings to see if the whales or the boats were making unique noises when the lines were reeled in. What they discovered was that the sound of the bubbles created by the revving of the propellers as the boat sped up and slowed down during the line-reeling process was calling the whales.

"It wasn't a piece of equipment; it was the way they handled the vessel," says Thode. "We finally convinced ourselves by going out on a vessel without gear. We put the engine into gear, and in less than 10 minutes we had 40-foot whales around the vessel." From their acoustic research, the team learned that the whales can hear this dinner bell from 3 miles away in stormy weather and up to 17 miles away on a clear day.

The next step was to understand how many whales were down there and how exactly they were eating, so the team attached underwater cameras to the fishing lines. "The most experienced whales learned they could bite the line and cause it to shake—like shaking apples off trees," Thode says. "The fish have soft mouths, so [the whales] could shake the fish off the line, and they don't have to risk getting their jaw caught on a hook."

The takeaway was that there was little—maybe nothing—that could deter the whales. They're too smart. Even attempts at playing a recording of the dinner bell sound from a decoy boat failed—the whales figured out that trick and went elsewhere for their meal. The team realized that deterrence was going to have to be replaced with a system of avoidance—figuring out where the whales were and alerting fishers so they could steer clear. So now begins the long and difficult process of attempting to attach satellite tags to the hunters so the fishers can know where they are and remain outside that 17-mile range of the whale's hearing ability. Andrews has managed to tag about seven whales so far by standing on a small inflatable boat and shooting the tags at each whale with an air gun. "You've got to wonder about our sanity sometimes," he says.

The fishers are also starting to get pretty good at visual identification. Sperm whales are easily differentiated by the markings on their tails, and SEASWAP's co-leader, marine biologist Jan Straley, has been able to photo-ID about 150 of the whales that spend their time in the gulf. Of those, about 12 to 15 are the worst perpetrators—including one whale the fishers have dubbed Zack the Ripper. "He's our bad boy," says Behnken.

But having the data isn't enough. To successfully avoid the whales, the fishers need to work together to get at least 17 miles away from the hunters. Though fishers are not in the habit of helping one another, Behnken says, she's been able to convince them that every time a whale gets dinner, it's receiving positive reinforcement. So using a combination of the satellite tagging maps and reports from fishers, Behnken and SEASWAP have been able to establish a makeshift whale reporting network. Early testing suggests it might work; next up is rolling it out to the whole fleet.

Meanwhile, the team has begun collaborating with other fisheries around the world where depredation is happening on a smaller scale (a group at the Crozet Islands, a French territory in the Southern Indian Ocean, is having trouble with killer whales, for example). And other organizations are starting to pick up on the acoustic techniques that SEASWAP has pioneered. But most of all, the scientists say, they will be benefiting from the unique relationship the research has developed between the fishers and the scientists.

"There are researchers all over the world that are envious of our relationship with our fishermen," says Straley. "They trust that what we're doing is going to be better for them and the whales in the end."