Pygmy killer whales aren't related to killer whales; they're not even whales. But that's almost as much as we know about these creatures. They're among the world's rarest cetaceans—hard to find and even harder to study. Now, however, scientists have tracked two pygmy killer whales for the first time in the Hawaiian Islands, giving researchers a glimpse of where these small cetaceans hang out.
Until the 1950s, pygmy killer whales (Feresa attenuata) were known only from two skulls collected in the 19th century and stored at the British Museum in London. Then, in 1954, a Japanese researcher, Munesato Yamada, had a chance to examine the skull and partial skeleton of one of the animals that whalers had killed. Yamada decided that some of the small whale's features resembled those of killer whales (Orcinus orca). Because it measured only 2.6 meters in length, Yamada suggested it was a dwarf form.
Since then, scientists have revised this classification, thanks to the study of other specimens. Researchers now agree that pygmy killer whales are most closely related to other smaller oceanic dolphins in the Delphinidae family, such as pilot whales, melon-headed whales, and false killer whales, says Robin Baird, a cetacean biologist at the Cascadia Research Collective in Olympia, Washington.
Baird directs a project to collect biopsy samples and photographs of the 12 species of marine dolphins that live around the Hawaiian Islands. During his team's studies, he and colleagues kept coming across pygmy killer whales. "About every 5 weeks, we encounter a pod," he says. From the project's 25-year records, Baird suspected that these pygmy killer whales were actually residents, living full-time in the islands, since some individual whales have been photographed several times over the years. If so, it would be the first resident pygmy killer whale population discovered.
To confirm his hunch, Baird managed to attach satellite tags via darts to the dorsal fins of two pygmy killer whales, one in 2008 and the other in 2009. "It's difficult to do," Baird says, "because you can't motor up to their groups." They dislike the sound of engines, and they swim away from approaching boats. So the scientists waited until they spotted a pod, then put their boat's motor in neutral and drifted silently toward the small whales. "They are curious, and if you're patient, they'll come over to investigate," Baird says.
One of the whale's tags transmitted its location for 10 days; the other, for 2 weeks. Using these data, Baird's team constructed a map of the whales' wanderings as they traveled about 4 kilometers offshore around the island of Hawaii. "They stayed surprisingly close to the island," says Baird. In contrast, a beaked whale (another small cetacean species) that his team also tagged traveled 500 kilometers away from Hawaii over a 20-day period.
The finding, which the team reports online today in Marine Mammal Science, "means we do have a resident pygmy killer whale population [in Hawaii]," says Baird.
And that means that scientists should keep an eye out for other island populations of pygmy killer whales elsewhere, says Robert Brownell, a cetacean expert with the Southwest Fisheries Science Center in San Diego, California. Also, he says, "close monitoring" measures will need to be developed to protect the Hawaiian population. In the meantime, he's hoping that researchers can glean a lot more data about these rare whales. "Any new information about this species is exciting and important," Brownell says. "We know so little about them."