Bowhead whales in Russia’s Okhotsk Sea are endangered, struggling to recover from threats both past (commercial whaling) and present (warming seas).
But that doesn't faze the local orcas, which have become skilled at hunting and killing the whales.
For the first time, scientists have witnessed, thanks to drone video, how the predators work as a team to surround and kill a juvenile bowhead, which can be three times heavier than an adult orca. (Read how orcas work together to whip up a meal.)
“We’ve known for a long time that orcas can hunt grey and bowhead whale calves by separating them from their mothers, but it’s interesting that here they kill a bowhead aged between one and five years old," says Olga Shpak, a biologist at the Severtsov Institute of Ecology in Russia who saw the hunt firsthand. The juvenile bowhead was already over 26 feet long and weaned from its mother, she says.
But this orca family, known to scientists since 2011, know what they're doing: They specialize in hunting juvenile bowheads. The matriarch's nickname is Whale Killer.
“Once they start to learn something, orcas will keep perfecting the skill, and this family has honed their hunting to require minimal energy,” Shpak says. (See an interactive graphic of orca hunting.)
Phil Clapham, leader of the Cetacean Assessment and Ecology Program at the Marine Mammal Laboratory in Seattle, Washington, says by email that whales often carry visible scars from failed orca attacks, but such events "are rarely observed."
"This is unique and extraordinary footage."
Adolescence is awkward for bowheads as they lose fat and bone acquired in their first year of life, redirecting body resources to develop their massive head and feeding apparatus, particularly the baleen plates that sieve zooplankton, their food source.
Unlike with bowhead calves and smaller whale species, such as minke, the orcas’ hunting strategy in this situation went beyond drowning their prey. (See the surprising reason why orcas attacked this blue whale.)
“This whale is too big to be drowned, so they ram its side, crushing the ribs,” says Shpak, who analyzed the video footage.
While the matriarch attacks in this manner, other pod members have assigned roles. The young orca swims near the whale’s head, blocking its escape, while other adult orcas pull the animal by the fins away from shallow waters.
“They can only kill the whale in deep waters because the orca needs to accelerate and gather enough speed for the strike,” says Shpak, who has seen this pod hunting bowheads four or five times. (See National Geographic's whale pictures.)
Orcas likely killed six bowheads in the Okhotsk Sea's Academy Bay in 2016 alone. The hunting pressure may be why the local whale population isn't bouncing back after commercial whaling in the 19th century and illegal Soviet whaling in the 1960s and '70s, Shpak says. Since the 1980s, Okhotsk bowhead numbers have hovered around 400.
"Whether such attacks represent a threat to the population is not clear," notes Clapham. "They are almost always on calves or yearlings (not adults), and we don't know how often they are successful."
Shpak adds “the presence of bowheads there is paradoxical to begin with,” because the bays of the western Okhotsk Sea are much warmer and less salty than the species' typically Arctic habitat. Colleagues studying bowheads in the Arctic routinely refer to the Okhotsk whales as “tropical," she jokes.
But that's also why the rare Okhotsk bowheads could be “a great model for studying how an Arctic species adapts to a warming climate."