Off Baja California in Mexico, a killer whale named after an Aztec emperor is leading his pod on routine takedowns of the largest fish in the sea: whale sharks.
There have been isolated reports in the past of killer whales (also known as orcas) attacking a whale shark. But a study, published Friday in the journal Frontiers in Marine Science is the first to show that a pod led by the 50-year-old Moctezuma has repeated the behavior at least four times. The finding suggests that the animals may be seeking out whale sharks.
Of the four documented events from 2018 through 2024, the large Moctezuma was present for three of them. And the fourth incident was carried out by killer whales that he is known to associate with.
You can find orcas in every ocean on Earth. Killer whales are actually the largest member of the dolphin family, but because dolphins are in fact a branch of the whale order, you might say that all dolphins are whales, while not all whales are dolphins. In a similar vein, whale sharks are not whales at all, but sharks, though like some whales, they are filter feeders.
While there is only one species of killer whale, scientists have documented that many orca populations are adapted to particular habitats. Each appears to prey on specific animals, including whale calves, seals, salmon, rays and great white sharks.
Whale sharks are gentle giants, but the coordinated assaults from Moctezuma and his pod are brutal, scientists report. The orcas ram the giant fish from below, flipping them over to induce a catatonic state. They also bite the whale sharks near their genitals, which causes them to bleed out before spiraling lifelessly into the abyss.
Their goal, according to Francesca Pancaldi, a marine biologist at the World Wildlife Fund and the lead author of the new study, is to get at the whale sharks’ large livers, which are stuffed with nutrients and calories.
Dr. Pancaldi points out that all the documented attacks have taken place against juvenile whale sharks, which are around 20 to 26 feet in length.
“The juveniles are definitely the most vulnerable,” Dr. Pancaldi said, when compared with bulkier adults, the largest of which have been documented to grow to more than 60 feet long.
At this time, Dr. Pancaldi and her coauthors do not believe that killer whale predation pressure poses a significant risk to whale sharks, which are internationally classified as endangered from threats like climate change, pollution and collisions with boats.
Alisa Schulman-Janiger, the lead field researcher for the California Killer Whale Project, said she found the study intriguing.
In 1992, a colleague had returned from a fishing trip in Baja with a story about seeing two killer whales attacking a whale shark. But Ms. Schulman-Janiger was never able to confirm the event.
Additionally, Ms. Schulman-Janiger, who was not involved in the research, has run into Moctezuma before. “We’ve had him at least twice in Southern California,” she said, in 2002 and 2017.
In both instances, Moctezuma was accompanied by a female. Ms. Schulman-Janiger wondered if the same female might now have been attacking the whale sharks, and, if so, whether she might actually be Moctezuma’s mother, who had instructed him in the ways of whale shark liver hunting.
Mothers and grandmothers are important in killer whale society. For instance, scientists have found that not only are orcas one of the few species to live past menopause, but adult male orcas that still have living mothers survive better than those that lack them.
While documenting orcas teaming up to attack whale sharks is new, the behavior has probably been happening on the high seas for a long time.
“The thing is that now there are more eyes, and everybody has access to iPhones,” Dr. Pancaldi said. “Everybody can take a picture or a video.”
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