For years, Japanese whalers have described a rare type of beaked whale unique to the waters of the Northern Pacific. Nicknamed Kurotsuchikujira, or black Baird’s beaked whale, the smaller bodied black cetacean has long eluded researchers but a new analysis of previously deceased specimens now finds that the Kurotsuchikujira is indeed its own species.

Preferring the deep oceans with a diving capacity of nearly 3,000 meters (9,850 feet), beaked whales are especially elusive making them one of the most difficult to study and poorly understood species of whales. In the North Pacific and its adjacent waters, there are two Berardius species, the slate-gray Baird’s beaked whale (Berardius bairdii) and the now-described black Baird’s beaked whale, or Berardius minimus, so named for its particularly small size.

Describing B. minimus for the first time in Scientific Reports, researchers collected four individual deceased whales – three from Hokkaido, Japan and another that was collected in Unalaska, off Alaska, in 1943 and held in the collection of the US National Museum of Natural History. All four whales “differed from their congeners” in morphology (body shape), osteology (skeletal structure), and molecular phylogeny (physical or genetic) characteristics.

Illustrations of (A) Berardius minimus, and (B) B. bairdii. The black bars show 1 m. In general appearance, B. minimus resembles a small B. bairdii with a proportionately shorter beak and more spindle-shaped body. Yoshimi Watanabe, National Museum of Nature and Science/Nature

"Just by looking at them, we could tell that they have a remarkably smaller body size, more spindle-shaped body, a shorter beak, and darker color compared to known Berardius species," said study author Tadasu K. Yamada in a statement.

Though whalers characterize B. minimus as black, the authors note that color differences between the two whales is mainly the result of scar tissue. Instead, they looked to the new whales’ relatively small body size, which measures just over 6 meters (20 feet) as opposed to B. bairdii's 10 meters (33 feet). B. minimus also has a distinctively shorter beak and other notable differences in the skull and skeletal makeup. A further DNA analysis indicated similarities only identified in the individuals from Hokkaido and Unalaska. But that is where the known ends.

Skull of the B. minimus holotype. (A) Dorsal, lateral. (B) Anterior and posterior views of the skull. (C) Lingual (inner, upper) and buccal (outer, lower) sides of the left mandible. (D) Buccal (external) view of the anterior (left) and posterior (right) teeth of the lower jaw. Nature

"There are still many things we don't know about B. minimus," said researcher Takashi F. Matsuishi. "We still don't know what adult females look like, and there are still many questions related to species distribution, for example. We hope to continue expanding what we know about B. minimus."

Whales in this part of the world are sometimes referred to as Karasu, or crow. Researchers say they are unsure whether Karasu and Kurotsuchikujira are the same species or in fact, represent a third new species as well.

Berardius minimus localities plotted against the B. bairdii distribution map. Circles show B. minimus localities. The white circle with a black X indicates the B. minimus type locality, whereas the black circle with the white X indicates the B. bairdii type locality. Nature