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Whale of a catch blows hole in family tree

Tokyo

A whale carcass swarming with maggots has made a splash in the world of marine-mammal research. The rotting remains were found by marine biologist Tadasu Yamada on a trip to a remote island in the Japan Sea in 1998 to examine a whale that died in a collision with a fishing boat.

Five years on, Yamada, of Tokyo's National Science Museum, and colleagues have shown that the whale represents a new species. The finding helps to resolve long-standing confusion about how many whale species there are. But it could create problems for whale conservation.

Scientists have long suspected that there are more than just the six recognized species of baleen whales of the genus Balaenoptera. Researchers thought that eight whales taken by Japanese research whaling boats in the late 1970s, for example, were part of a unique species — but they couldn't prove it.

Shiro Wada, a molecular biologist at Japan's National Research Institute of Fisheries Science in Yokohama, analysed enzymes in the liver and muscle of those specimens and found dramatic differences from common Bryde's whales (Balaenoptera brydei) which they resembled.

“I was sure that they were a different species, but that was a period when people didn't trust comparative enzyme studies for evolutionary studies,” says Wada. The full carcasses of the whales were not kept for further study.

Analysis of the skull of a baleen whale found in 1998 suggests that it represents a new species. Credit: T. YAMADA, Y. TAJIMA & K. ARAI

So when the 1998 whale carcass turned up, Wada, Yamada and their colleagues compared the structure of the skull and baleen plates — sieve-like structures that baleen whales use to sift food — along with DNA from all nine whales, with other Balaenoptera whales. They conclude that all nine are members of a previously unknown species. They also confirm that Eden's whale (B. edeni) is distinct from Bryde's whale, bringing the total number of Balaenoptera species to eight.

The identification of the new species, announced on page 278 of this issue, should help inform estimates of whale abundances, says Justin Cooke, senior scientist at at the Centre for Ecosystem Management Studies near Freiburg, Germany, and a member of the World Conservation Union's Species Survival Committee. The union does not know how many Bryde's whales there are, because of confusion over the number of species.

The Japanese whaling community, which catches about 50 Bryde's whales in the western northern Pacific each year for research purposes, estimates that there are 22,000 Bryde's whales in that part of the ocean.

Researchers at the Institute of Cetacean Research in Tokyo, who carry out much of the research whaling, deny that they are catching the new species. “We only catch the common Bryde's whale,” says Luis Pastene, a population geneticist at the institute.

But Scott Baker, who studies whale population genetics at the University of Auckland, New Zealand, reckons that they can't be so sure. “Japan has been conveniently ignoring the taxonomic uncertainty,” says Baker. “Until you understand the taxonomy, you can't be sure how many are out there or what you're hunting.”

Baker adds that genetic methods are likely to uncover more 'hidden' biodiversity in the oceans over the next few years. But he doubts that there are many more baleen species left to find.

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