Elusive Marine Mammal Uses Interspecies Buddy System
What ocean mammal is a rare bird but not a lone wolf? Meet the false killer whale. You're not likely to ever spot one in the wild, but if you do, it won't be alone. These animals prefer to travel with a crowd—not just of their own species, but also including their closest companion, the bottlenose dolphin.
False killer whales are so named because the look a little like killer whales, or orcas.* Yet unlike their showy namesake, false killer whales are rarely encountered by humans. In most places where we know they live, it's only because they've turned up stranded on the shores. We don't even know whether they migrate with the seasons.
We do know that the whales are social, and that they sometimes pal around with other species. Jochen Zaeschmar, a master's student at Massey University in New Zealand, has been rescuing and studying false killer whales and other species since 2000. This summer he published a paper reporting that false killer whales sometimes partner with bottlenose dolphins to hunt. On two occasions, researchers had come across large groups of the whales and dolphins apparently working together to round up fish. They blew bursts of bubbles to herd their prey into one helpless crowd, then feasted.
For Zaeschmar's latest study, he and other researchers gathered up records of false killer whale sightings along the northeast coast of New Zealand between 1995 and 2012. It was a total of just 47 encounters—on one whale-watch boat, false killer whale sightings happened on less than half of one percent of trips.
The observations of whales and dolphins hunting together had been no (ahem) fluke. When false killer whales were seen, bottlenose dolphins were by their side "virtually all the time," Zaeschmar says—in 43 out of the 47 sightings.
"Increasing the size of your group...increases the chances of finding food," Zaeschmar explains. The prey fish hunted by these mammals are plentiful, but spread out. Working together could help the hunters find their prey, he says, and "once they do find it there won't be any competition, because there is enough for everyone."
It's also possible, Zaeschmar notes, that one species is just taking advantage of the other's superior hunting skill. The dolphins and whales seem to be working in a true partnership. But "it's difficult to really prove it."
Either way, hunting was happening during less than half of the mixed-species encounters. Yet the animals—anywhere from dozens to hundreds of them at a time—behaved like a single group. There must be some other reason they seek each other's company. "Social factors might play a role," the authors write. Staying in large groups might also help the animals keep an eye out for their own predators, which include (real) killer whales.
The researchers were able to identify some individual animals using distinctive marks and scars on their bodies, such as bites from cookie-cutter sharks (named for the shape of the bite they take out of their victims). Spotting certain animals over and over, the scientists could build a rough map of the animals' social structure. They found that "long-term associations exist between the two species," Zaeschmar says, "with some of the same dolphins observed together with the same whales [over] at least 5 years and 650 kilometers."
"These associations appear to be stable," he says. The two species stick together, whether they're ruthlessly rounding up prey or surprising a boatful of very lucky humans.
*Technically, both the false killer whale and the real killer whale are types of dolphins. But just because marine biologists like to make their lives difficult doesn't mean we have to, so I refer to the false killer whale here as a "whale."
Images: (top) Mazdak Radjainia, (bottom) David Hall.
JOCHEN R. ZAESCHMAR, INGRID N. VISSER, DAGMAR FERTL, SARAH L. DWYER, ANNA M. MEISSNER, JOANNE HALLIDAY, JO BERGHAN, DAVID DONNELLY, & KAREN A. STOCKIN (2013). Occurrence of false killer whales (Pseudorca crassidens) and their association with common bottlenose dolphins (Tursiops truncatus) off northeastern New Zealand. Marine Mammal Science DOI: 10.1111/mms.12065
Jochen R. Zaeschmar, Sarah L. Dwyer, & Karen A. Stockin (2013). Rare observations of false killer whales (Pseudorca crassidens) cooperatively feeding with common bottlenose dolphins (Tursiops truncatus) in the Hauraki Gulf, New Zealand. Marine Mammal Science DOI: 10.1111/j.1748-7692.2012.00582.x