For the first time, researchers are tracking by satellite a group of “tropical oceanic” killer whales, a type rarely seen and almost a complete mystery to scientists.

Researchers from Olympia-based Cascadia Research were in Hawaii, on the final day of a 15-day research cruise to study marine mammals, when they encountered four killer whales offshore from Kona. They were the type of orca known to roam the open ocean, but rarely seen by human observers.

In fact, in 14 years of research work in Hawaii, Cascadia’s Robin Baird said he has encountered these tropical killer whales only three times twice before. Others have seen them on occasion, but sightings are few and far between.

This time, on Nov. 1, Baird’s crew was able to obtain samples of skin for genetic work, which will help determine how closely these whales are related to other orcas throughout the world. The crew also attached satellite transmitters to three of the four whales.

Two of the transmitters are still transmitting nearly two weeks later, and Baird hopes at least one will continue working for several more weeks. In warmer waters, the barbed “tags” tend to fall off sooner than in Northwest waters, Robin told me. As you can see from the map, the whales first moved west, then north, then west again. As of the latest plot this morning, they were west and slightly south of Kauai.

By coincidence, two underwater photographers captured video and still photos of these killer whales around the time the Cascadia crew was in the area off Kona. Deron Verbeck and Julie Steelman told KHON-TV that the experience was the pinnacle of their career. (See video below.)

Although Nov. 1 was the last official day of the Cascadia cruise, researcher Russ Andrews and several others went back out on Saturday to find the four killer whales. They spotted three other orcas with them. During the outing, they observed predation on a thresher shark, something that photographer Verbeck also reported.

These tropical oceanic killer whales are smaller than the familiar resident and transient killer whales of the Northwest, Robin Baird explained. Instead of a white “saddle patch” near the dorsal fin, these animals have a gray, almost black patch that is difficult to see.

These are not the “offshore” killer whales that roam miles of the West Coast, but generally stay on or near the continental shelf, Robin told me. Still, it will be interesting to see if the tropical oceanic orcas are closer genetically to the offshores, which are known to eat sharks.

We do know the Southern Resident orcas, which frequent Puget Sound, specialize in eating salmon, particularly chinook. But Robin says whales feeding in the open ocean probably don’t encounter enough of any one prey type to be so specialized. Considered generalists, they have been known to eat squid, sharks, dolphins and occasionally larger whales.

Robin says little is known about how they group together, because the number of photo identifications is small. Generally, the groups are five or less. The groups are likely to be families, including a female and all her offspring. This is the same type of matriarchal society found in other orca groups, although in some orca societies — such Southern Residents — one matriline often joins with others.

Robin says just about everything learned about their travels is new, “from short-term movement rates, habitat use, and — if the tags stay on for a while — how often they may visit island-habitats (and) whether they cross international boundaries.”

In addition to Robin Baird and Russ Andrews, the research crew on the trip included Daniel Webster, Annie Douglas and Annie Gorgone, all from Cascadia; Amy Van Cise from Scripps Institution of Oceanography and several volunteers.

Even before the killer whale encounter, the cruise was considered successful, Robin said. Twelve species of marine mammals were encountered, and satellite tags were deployed on six species, now being tracked. More than 40,000 photographs were taken, some of which are shown on Cascadia’s Facebook page or the project page on Cascadia’s website.

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