Until the 1970s, Pitman noted, all killer whales, also known as orcas, were considered one species that occurred around the world from the Antarctic to the Arctic and ate anything they could find.
The picture changed when researchers identified three types of killer whales in the North Pacific.
The three types do not interbreed. "In fact, they completely avoid each other," said Pitman, whose studies of Antarctic killer whales are revealing patterns similar to those in the North Pacific.
While scientists are hesitant to call the whale types different species because their differences could be the result of environmental factors, the whales are "clearly on a trajectory to become separate species," Pitman said.
He noted that their distinct food and habitat preferences, size differences, and perhaps even different vocalizations are all barriers to reproduction.
"At some point, they won't be able to interbreed even if they wanted to," Pitman said.
This May, Pitman co-authored a paper in the journal Biology Letters that found genetic differences that are consistent with reproductive isolation among the three types of Antarctic killer whales.
John Ford is a killer whale expert with Fisheries and Oceans Canada's Pacific Biological Station in Nanaimo, British Columbia.
He said the Antarctic studies fit with the global picture that killer whales represent a complex of populations that function as different species even though they are not yet scientifically described as such.
Ford added that the addition of the satellite tagging technology that Pitman used on his most recent study of killer whales will help "focus our conservation efforts for particular populations that might be in trouble."
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