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Seabirds are skilled opportunists, commonly flocking to fishing boats to scavenge on scraps thrown overboard. Now, researchers have documented one large, notoriously aggressive species exploiting fishing operations in an unusual way—by taking bites out of the whales they attract.
In 2015, Jared Towers, a cetacean ecologist at the British Columbia–based research organization Bay Cetology, boarded a fishing vessel that was in search of Patagonian toothfish, a lucrative cod species also known as Chilean sea bass. Towers wasn’t interested in the fish, but in the sperm whales they lure—the whales have learned to pilfer meals off the fishers’ longlines. While at sea in the South Atlantic, Towers noticed something bizarre: just as a sperm whale surfaced to breathe, a giant petrel swooped down and ripped a morsel of skin and blubber out of its back.
On that trip alone, Towers saw giant petrels take bites out of surfaced whales more than a dozen times. Combining his sightings with those made by fisheries observers between 1997 and 2019, Towers and his colleagues report in a new paper 23 cases of giant petrels preying on whales. “That’s a minimum,” Towers says.
Though the idea of birds eating live whales is surprising, this isn’t the only instance of birds feeding on much larger animals. Researchers have previously witnessed giant petrels biting live sheep, and oxpeckers consuming rhinoceroses’ skin and blood. And like giant petrels, kelp gulls have been known to peck at whales, too.
Off the coast of Argentina’s Valdes Peninsula, kelp gulls’ attacks on southern right whales can last more than an hour, says Mariano Sironi, scientific director of Argentina’s Instituto de Conservación de Ballenas (Whale Conservation Institute) who was not involved in Towers’s research. He says the relentless pecking creates craters in the whales’ skin, and causes a great deal of stress for the animals.
Those attacks have intensified in recent years, he adds, in part because discarded food from fishing boats and open-air dumps is sustaining an artificially large gull population. From the 1970s to the 2000s, the proportion of whales with gull wounds increased from two to 99 percent. Sironi says the birds’ assaults may also be contributing to the area’s high death rate for whale calves.
Researchers, Sironi says, might be witnessing the beginning of a growing problem in the subantarctic, similar to what scientists began recording in Argentina five decades ago.
For now, giant petrels aren’t attacking whales nearly as often as kelp gulls are. But just as human activities inflated the gulls’ numbers, the same could prove true for giant petrels—with potentially harmful results for the whales.
“Because longlining activities provide feeding opportunities for whales and birds, you have these unnaturally large aggregations of both,” Towers says. Whales also dive deep, fast, and for long periods when stealing fish off the longlines, which forces them to spend several minutes at the surface to catch their breath. That may be offering petrels the perfect opportunity to take a bite.
Towers says the birds’ new taste for sperm whale highlights how nearly every human activity affects ecosystems—sometimes in unexpected ways.