Washington, September 22 : Scientists have used DNA evidence to identify 113 new sharks and rays in Australia, which includes a skinny saw shark, a swell shark that looks like it swallowed a Frisbee, and a river shark.
According to a report in National Geographic News, nearly half of the newly named sharks and other species are found only around Australia.
The discoveries increase the continent's tally of known sharks and rays by a third. ne of the new fish, the collared carpet shark, is so rare that the only known specimen was found in the belly of another shark. Some of the new species are already threatened with extinction, according to scientists, and many of the sharks and rays have yet to be named.
During the 18-month study, researchers used genetic techniques to help scientifically describe, for the first time, species already in museum collections in Australia, New Zealand, and Europe.
"We reviewed the entire shark and ray fauna," said fish taxonomist Peter Last, who led the project for Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO). "Existing descriptions, many of them brief and lacking detail, weren't much help," he added.
At first glance, some of the fish appear very similar, making it tough to tell different species apart. Some even share the same habitat.
But, by analyzing the species' DNA, the scientists were able to uncover invisible distinctions.
"In some cases, what was thought to be a single species of shark turned out to be something like five species," said Last.
Among these previously "hidden" species is the newly described maugean skate, already listed as endangered by the International Union for the Conservation of Nature.
Found in "three little estuaries" off the Australian island of Tasmania, the maugean skate is very similar to a species found on the other side of the world, off southern South America.
According to Last, the similarity of the two skate species suggests that they were once a single species that plied Gondwana coastal waters. Since the breakup, the skates have hugged the coasts of Australia and South America.
"These animals have simply remained on the edges of the fragments of (the former Gondwana continental) plate all that time, without changing much-though enough to now be considered separate species," he said.
Most of the new species-such as the southern dogfish, a gulper shark-live along Australia's continental shelf, a very narrow plateau that plunges steeply to the open deeps.
According to Clive Roberts, curator of fish at the Museum of New Zealand, new large marine species will continue to turn up.
"We're still describing new species from 10 or 13 feet (3 or 4 metres) depth, so it's no surprise that there are heaps of undescribed stuff further down," he said.