CORVALLIS, Ore. – A new genetic study concludes that humpback whales in three different ocean basins are distinct from one another and are on independent evolutionary trajectories – and should be considered separate subspecies.
The research, led by scientists from the British Antarctic Survey and Oregon State University, is being published this week in Proceedings of the Royal Society B.
The new study builds on previous research led by Scott Baker at Oregon State and published in December 2013, which identified five distinct populations of humpback whales in the North Pacific Ocean. This latest study found that populations of humpback whales in the North Pacific, North Atlantic and Southern Hemisphere are more distinct than previously thought.
Lead author Jennifer Jackson, of the British Antarctic Survey, said that despite seasonal migrations by humpback whales of more than 16,000 kilometers, whale populations are more isolated from one another than previously thought.
“Their oceanic populations appear separated by warm equatorial waters that they rarely cross,” Jackson said. “But until this study, we didn’t realize the extent of long-term isolation between the North Pacific, the North Atlantic and the Southern Hemisphere.”
Humpback whales are listed as endangered in the United States under the Endangered Species Act, but had recently been downlisted by the International Union for the Conservation of Nature on a global level, according to Baker, who is associate director of the Marine Mammal Institute at Oregon State’s Hatfield Marine Science Center in Newport, Ore.
However, two population segments recently were relisted as endangered by the IUCN – one in the Sea of Arabia, the other in Oceania (the South Pacific) – and it is likely that at least one of the newly identified populations in the North Pacific will be considered endangered, Baker pointed out.
The newest findings – that humpback whales in the world’s major ocean basins are genetically different – should change the way scientists and resource managers look at these animals, the researchers say.
“This has implications for how we think about conservation of humpback whales,” Baker said. “We now propose that oceanic populations should be recognized as subspecies. Within ocean basins, we would also recognize a number of ‘Distinct Population Segments’ – each of which has a different history of exploitation and recovery.”
The researchers gathered genetic samples from free-swimming humpback whales using a small biopsy dart and then analyzed both mitochondrial DNA inherited from the mother and nuclear DNA from both parents. Mitochondrial DNA enabled the researchers to trace the exchange of female humpback whales among the world’s oceans over the past million years; the nuclear DNA provided insight into male interchange and reproductive isolation.
“We found that although female whales have crossed from one hemisphere to another at certain times in the last few thousand years, they generally stay in the ocean of birth,” Jackson said. “This isolation means oceanic populations have been evolving independently on an evolutionary time scale.”
In addition to Jackson and Baker, the project team included researchers from Florida State University, James Cook University, University of Auckland, Fundacion CEQUA, Wildlife Conservation Society, the American Museum of Natural History and the South Pacific Whale Research Consortium.
The study was funded by the New Zealand Royal Society Marsden Fund and the Lenfest Ocean Program.