Researchers working in Hawaiian waters have identified the world's first genetically distinct population of false killer whales.

Evidence that Hawai'i's small population of false killer whales is genetically different from populations elsewhere in the tropical Pacific could justify additional protection measures for the animals, said biologist Robin Baird of the Cascadia Research Collective in Olympia, Wash.

"The main implication is that it puts the population more at risk than if the whales around Hawai'i were part of a large open-ocean population. Any small population of animals is more susceptible to impacts from human activities and variations in the natural environment," Baird said. "If we determine they are reproductively isolated, there may be a need for attention to how people manage or mitigate those impacts."

The discovery was based on analysis of small skin samples collected over a five-year period from free-ranging false killer whales and animals hooked in the local longline fishery.

"It was a surprise because false killers whales are widely distributed and are known to travel long distances, and this group has clearly been isolated for a long time," said NOAA fisheries research biologist Susan Chivers of the Southwest Fisheries Science Center in La Jolla, Calif.

Although the toothed whale is found in tropical seas around the globe, little is known of the species because the animals inhabit the deep ocean and are rarely seen.

"Because they tend to live in the open ocean, there's really been virtually no research done on them," Baird said. "It's one of a handful of species that mass-strands, so most of what's known has come from mass-stranding events."

The deep water close to shore makes Hawai'i one of the better locations to study the species, he said, but even here they are difficult to observe because of their low numbers, estimated at 270 individuals.

Around the main Hawaiian Islands, false killer whales feed primarily on mahi mahi and yellowfin tuna. Baird said the Hawaiian population probably developed as a distinct group because the wide expanses of ocean surrounding the island chain are "a biological desert" in terms of providing a food source for the animals.

MANY QUESTIONS

Despite their name, false killer whales are really a species of dolphin, not whale. They earned their common name because like orcas, which also are a species of dolphin, false killer whales have been known to attack other dolphins and whales.

They are social animals and typically swim in pods of 10 to 20 that belong to larger groups of up to 40 individuals, and can be found traveling with bottlenose dolphins and other cetaceans.

False killer whales also are notorious for stealing fish from baited longlines. Chivers said an average of one or two false killer whales are killed or injured annually while interacting with Hawai'i's longline industry, which operates about 50 miles or more from shore.

Two of the many other questions marine biologists have about false killer whales is whether the animals interacting with the longline fishery are part of the Hawai'i population, and just how far they roam.

"We know that these animals around the Hawaiian Islands are genetically distinct, but we don't know how far offshore they go and how they overlap with the open-ocean population," Baird said.

Baird, who returns to Hawai'i next week to conduct further research, said false killer whales are known to swim between O'ahu and the Big Island, but it's a mystery whether they also venture farther north to Kaua'i and the Northwestern Hawaiian Islands.

He hopes to place temporary tags on some of the animals to track their movements via satellite over the course of several months.

PHOTO DATABASE

Another of Baird's ongoing projects is a false killer whale identification database based on photographs of the scars and notches in the marine mammal's dorsal fin. A similar effort was conducted off Costa Rica, but the Hawai'i photo project is the longest-running detailed study of its kind, Baird said.

Because of the rarity of false killer whale encounters, he encouraged anyone who has taken photos of the creatures to contribute them to the identification project.

Photos can be e-mailed to him at rwbaird@cascadiaresearch .org.

Also participating in the genetic research were Nicole Hedrick and Juan Carlos Salinas of the Southwest Fisheries Science Center, and Daniel McSweeney and Daniel Webster of the Wild Whale Research Foundation in Holualoa.

A paper on their research will be published online Saturday in the Canadian Journal of Zoology.