The number of rorqual whale species swimming in the world's oceans has jumped to eight from six, according to new research by a team of Japanese scientists published in tomorrow's issue of the science journal Nature. The research shows that rorquals commonly referred to as Bryde's whales actually represent three distinct species.

Rorqual whales (Balaenoptera) do not have teeth. Instead they have baleen, a horny substance found in rows of plates along their upper jaws, and they are thus classified as baleen whales. They range from about 26 to 92 feet (8 to 28 meters) in length and weigh upwards of 220,000 pounds (100,000 kilograms).

Rorquals are found throughout the world's oceans and are distinguished by their long bodies and pleated throats. Their most familiar species are the common minke whale (B. acutorostrata) and the blue whale (B. musculus).

The Japanese scientists identified a new species of rorqual, Balaenoptera omurai, and resolved a long-standing debate by showing that other whales previously referred to as Bryde's whale are indeed distinct species: (B. brydei) and (B. edeni).

"It was not a big surprise to me that we encountered the species we described," said Tadasu Yamada, a biologist at the National Science Museum in Tokyo and co-author of the research describing the species.

Scott Baker, an associate professor of population genetics and evolution at the University of Auckland in New Zealand, said limited access to the holotype of B. edeni (a holotype is the museum specimen that represents the species for taxonomic purposes) and to other specimens of the rarer B. omurai had previously prevented the scientific community from closely studying the various Balaenoptera species.

Yamada and colleagues Shiro Wada of the National Research Institute of Fisheries Science in Yokohama and Masayuki Oishi of the Iwate Prefectural Museum in Morioka, gained access to the specimens and based their conclusions on a comparison of the species' morphology (body form), bone structure, and DNA.

"Scientists, noted Yamada, rely on access to museum specimens-many of them more than 100 years old-to do their work. By applying improved techniques to these specimens, the researchers can mine new knowledge-in this case an improved understanding of taxonomy.

"The basic conclusion that there are a number of taxa from a single group is sound," said Baker. "But there will be some skepticism about how they were able to resolve the previous taxonomy because of the nature of the holotype specimens."

Bryde/Sei Complex

Since Wada noted a distinct Bryde's whale in a 1991 study and Baker and his colleagues found B. edeni in Korean markets in 1994, there have been scientific murmurings that there could be "more than one species in the group of whales known as Bryde's whale," said Yamada.

The confusion over the Balaenoptera species dates back to the original description in 1878 of a specimen stranded in Burma and now located in a museum in Calcutta, India, as B. edeni. A second species found in 1913 off the coast of South Africa was informally described as B. brydei.

In 1950, a Norwegian scientist concluded that B. edeni and B. brydei were the same species and per protocol recognized the species as B. edeni since that was how it was first described. Bryde's whale was retained as the common name.

Then, in the 1970s, Japanese researchers killed what they believed were Bryde's whales from ocean waters around Indonesia and the Solomon Islands. In 1991, Wada recognized these eight specimens as distinctive from all other rorquals, including Bryde's whales.

To make things even more confusing, Bryde's whales, from a distance, look a lot like Sei whales (B. borealis), said Baker. The differences are notable only upon close inspection of the morphology.

"We've tended to think of this as the Bryde/Sei whale complex," said Baker. "It is not clear how many species it might include or who is most closely related to whom."

Species Determination

Yamada, Wada, and Oishi compared the morphology, bone structure, and mitochondrial DNA of the eight specimens killed by the Japanese researchers in the 1970s with that of one whale that washed ashore a coastal island in the Sea of Japan in 1998.

As a whole, the researchers determined from outside appearance this group of specimens most closely resemble a smaller version of the fin whale (B. physalus), but owing to differences in skull shape, baleen plates, and DNA they concluded that the group represents a new species of baleen whale, B. omurai.

According to the description in Nature, B. omurai has an adult body length of less than 40 feet (12 meters) long, a relatively broad and flat skull, and a mouth that tapers from its base.

Based on morphological differences, the researchers also concluded that Bryde's whale and Eden's whale are distinct from each other as well as distinct from the new species, B. omurai.

Baker said that analysis of DNA from the B. edeni holotype specimen in Calcutta and morphological examination of additional specimens would be important to confirm the new taxonomy.

Yamada's team was not able to obtain a DNA sample of the B. edeni specimen in Calcutta but instead used DNA from a matching specimen at the National Museum of Natural History, in Leiden, Netherlands.

"They are basically making the argument that the edeni holotype is different from the new species, omurai. If that is right, the proposal to name the new species is valid," said Baker, who added that regardless of the nomenclature, the clarification of the species-level differences is biologically sound and important for conservation.

Whale Abundance

The next challenge for the Japanese researchers, said Yamada, will be determining the relative abundance and distribution of B. omurai, B. edeni, and B. brydei.

Yamada is currently aware of ten B. omurai specimens stored in museums around the world that were misclassified as Bryde's whales and he expects more to be found in the oceans.

"If we are careful in getting information from stranded animals, we can make some distribution patterns of these three species," he said.

Baker said that understanding the abundance of the various Balaenoptera species is critical because the Japanese have proposed to the International Whaling Commission (IWC) a commercial hunt of Bryde's whales.

"Currently, all baleen whales are protected by an international moratorium on commercial hunting. If this moratorium were to be overturned, however, you need to understand both taxonomic identity and population structure in order to estimate abundance and calculate an appropriate catch limit," he said.