Scientists have identified a rare new species of beaked whales with a size of up to seven metres that ranges from northern Japan across the Pacific Ocean to Alaska's Aleutian Islands.
Japanese whalers call the enigmatic black whales "karasu," the Japanese word for raven. The new species is darker in colour and about two-thirds the size of the more common Baird's beaked whale, but so scarce that even whalers rarely see them, researchers said.
A DNA analysis of 178 beaked whales from around the Pacific Rim found eight known examples of the new species.
"The challenge in documenting the species was simply locating enough specimens to provide convincing evidence," said Phillip Morin from US National Oceanic and Atmospheric Administration Fisheries' Southwest Fisheries Science Centre.
"Clearly this species is very rare, and reminds us how much we have to learn about the ocean and even some of its largest inhabitants," said Morin.
An earlier Japanese study had suggested that the black whales, sometimes considered a dwarf form of Baird's beaked whale, might represent a new species, researchers said.
That sent Morin in search of additional genetic samples to definitively answer the question and better understand the range of the elusive species.
He turned first to the Southwest Fisheries Science Centre's marine mammal tissue collection and found two samples that appeared to represent a new species.
One came from a whale found in Alaska's Aleutian Islands in 2004. Then Morin and his colleagues pursued additional DNA samples from museums, research institutions and Japanese markets where whale meat is sold.
In 2014 scientists found a dead beaked whale on St George Island in the Bering Sea. Genetic tests later showed it to be the new species.
DNA analysis shows that the new species and Baird's beaked whale are each more closely related to Arnoux's beaked whale from the Southern Hemisphere than they are to each other.
The genetic differences and smaller size indicate that the black whale is distinctive enough to represent a new species, the scientists found.
Official recognition and naming of the species awaits a formal review of the animal's characteristics and differences from other beaked whales.
Beaked whales remain among the least known whales in the ocean, with several species identified only in the past few decades.
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