Whales of distinction: old specimens now declared a new species.

Japanese scientists have named a new category of living baleen whales to explain a series of puzzling specimens that has been accumulating since 1976.

Members of the just-identified species, Balaenoptera omurai, look like fin whales but have distinctive physical and genetic characteristics, report Shiro Wada of the Fisheries Research Agency in Yokohama, Japan, and his colleagues. Distinguishing marks include a broad, flat head with a uniquely shaped central joining of the skull bones. In its mouth, this whale has unusually few of the baleen plates that such whales use to filter food from the water. The researchers report in the Nov. 20 Nature that their analysis brings the number of known living baleen whale species to eight, although other scientists come up with different totals.

Classifying whales presents special problems that don't plague catalogers of mice, comments James G. Mead of the Smithsonian Institution in Washington, D.C. Whale specimens are too large to store and ship readily, for example, and some of the taxonomy relies only on observations at sea. Although he and his colleagues named a new beaked whale only last year, Mead says that scientists generally describe a whale species perhaps once a decade.

Wada traces his interest back to work he did in the late 1970s on eight whales captured by Japanese research-whaling ships in the Solomon Sea and the eastern Indian Ocean. After he analyzed variations in certain enzymes, he suspected that the specimens represented a new species. When Wada compared the bones of these whales to museum-preserved skeletons of other whales, he strengthened his case.

In 1998, just after Wada had finished drafting a manuscript that described the new species, a carcass turned up on an island in the Sea of Japan. The whale looked like the eight that he'd included in his report, so Wada abandoned his draft and joined the analysis of the new specimen. It was preserved by Tadasu K. Yamada of the National Science Museum in Tokyo, a coauthor of the new paper.

The researchers sequenced a section of 900 or so nucleotide building blocks in the DNA of the fresh specimen, two of the older ones that Wada had included in the proposed new species, and some other whales. DNA differences between the newest find and the specimens tentatively assigned to the new species were less than one-tenth as great as those between any of these whales and the others.

The new name, B. omurai, honors the late Japanese cetologist Hideo Omura. However, Mead cautions that it's too early to tell whether the thicket of earlier whale nomenclature includes a name that might preempt this one.

Mead says he's not surprised that a new species has turned up on this branch of the whale family tree because specialists have recognized confusion there for at least 2 decades. Straightening out the whole complex would take an entire career, he says. "At least, this [new paper] ties down the description of one species," Mead says.