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Ten-year-old Moonstar is a humpback whale who’s been hanging around the same Vancouver Island, British Columbia, cove long enough to become a favorite with local researchers. But even cetacean celebrities have secrets, and in 2011, Moonstar let one slip: a crafty and previously unseen hunting strategy.
Since then, researchers have observed the behavior, known as trap feeding, spreading among local humpbacks. It is thought to be a way of making mealtime more efficient when prey is scarce.
Vancouver Island humpbacks typically lunge feed, which involves charging toward a school of fish and engulfing it in one fell swoop. Lunge feeding is effective, but it takes a lot of energy. When a whale opens its mouth, the action creates a lot of drag—enough to slow a lunging leviathan to a near halt.
This means it has to accelerate a second time just to get moving, explains Christie McMillan, executive director and director of humpback whale research for the Marine Education and Research Society (MERS), based on northern Vancouver Island. “You need a pretty big and dense school of fish to make lunge feeding worth the effort.”
Trap feeding, in contrast, is more energy efficient when fish are spread out. When fewer calories are readily available, Moonstar and his fellow trap feeders opt to laze at the surface, mouths agape, and wait for prey such as juvenile herring to swim inside. “It reminded us of a Venus flytrap,” says McMillan, who recently published a report on the behavior along with her MERS colleagues. Some individuals even use their sizable pectoral flippers to flick fish into their mouths while they wait.
It’s not surprising that humpbacks are getting creative with fishing: the species is known for innovative techniques, including blowing bubble nets to corral prey. Researchers have also documented feeding strategy shake-ups elsewhere in the world. On North America’s east coast, for instance, humpbacks learned to slap the surface with their tail flukes during hunting, possibly to deter their sand lance prey from jumping out of the water. The arrival of this hunting behavior, known as lobtail feeding, was associated with a change in diet after herring populations declined. Trap feeding also seems to have arisen in response to shifting ecological conditions. The Vancouver Island humpbacks are still eating off the same menu, but their favorite piscine fare seems harder to come by.
To increase their chances of feeding success, this cohort of whales appears to be getting a helping hand from birds. Trap feeders tend to lurk beside groups of gulls and diving birds, such as rhinoceros auklets, that drive diffuse schools of fish closer together and potentially into the mouths of whales. As well, fish are known to hide in boat shadows and under rocky outcrops so could be tricked by the similar silhouette cast by a bobbing ocean giant. Herring may move toward the whale in a misguided attempt to avoid becoming bird food.
Trap feeding won’t replace lunge feeding, the researchers note, but once an individual learns the new behavior it will continue to use it. Exactly how the strategy is passed around remains a mystery, but the team doesn’t believe it’s a family affair.
“Moonstar was one of our first trap feeders, but his mother has never trap fed,” says McMillan. When the behavior was first observed eight years ago, only Moonstar and one other whale were trap feeding. Now, more than 20 have caught on. Humpback whales don’t mature until they’re between five and nine years old, and they only give birth every few years, so if mothers were passing trap feeding to their calves, the researchers think the behavior’s spread would have been slower. “It seems to be more about who you hang out with and where you hang out,” McMillan says.
Interestingly, Bryde’s whales in Thailand have begun employing a similar passive feeding tactic, known as tread-water feeding, when schools of fish are diffuse, and they too get some avian aid.
The MERS team is excited to see where else the behavior pops up over the coming years and encourages anyone who believes they’ve seen a trap feeder to get in touch, especially with video footage.
Good fishermen work in ways that make sense for the region, the catch they’re looking for, and the day’s conditions. As ocean habitats continue to change, it seems that humpback whales might be doing the same.