DHAKA: The world’s largest population of vulnerable Irrawaddy dolphins — famed as aquarium attractions — has been found in Bangladesh’s waters, according to a five-year wildlife study.

Until now, it was believed the small light-grey mammal was threatened and the International Union of Conservation of Nature had put five of its Southeast Asian populations on its list of critically endangered animals.

But the study, launched in 2003 by the New York-based Wildlife Conservation Society and the Bangladesh Cetacean Diversity Project, has counted 5,832 Irrawaddy dolphins along Bangladesh’s coast and estuaries.

“It’s by far the biggest population of Irrawaddy dolphins in the world,” said project director Brian Smith of the Wildlife Conservation Society.

“It’s very good news for all of us,” he said. The researchers surveyed the waters along Bangladesh’s 1,400 kilometres (870 miles) of coastline, said Rubayat Mansur, who led the research team.

“We’re absolutely thrilled to make such an important discovery... We don’t know any other place where these dolphins are found in such large numbers,” he told AFP.

In other areas where the dolphins are known to converge, such as the Mekong delta, populations have been estimated at less than 100.

“It’s great news if the researchers have in fact found such a huge number of Irrawaddy dolphins off the Bangladesh coast,” said Switzerland-based Liz Mc Lellan of environmental group WWF. “We’ll look into the study because we know only a very small population of Irrawaddy dolphins now live in Southeast Asia,” she told AFP.

Although its name is derived from Myanmar’s biggest river, the two-metre long Irrawaddy dolphin is mainly an oceanic mammal that favours coastal waters and estuaries.

They are found in small, geographically isolated populations from Australia to India to the Philippines.

One of the main threats to their survival is drowning in fishing nets, says the WWF. They are also fished for their oil and meat.

The dolphins’ ability to live in both salt water and fresh water makes them popular with dolphin shows, where fresh water tanks are cheaper to maintain.

Mansur said many of the dolphins had been found in the world’s largest mangrove forest, the Sundarbans which straddles Bangladesh and India.

The forest is also home to 400 Ganges sweet-water dolphins which also are on the endangered list.

Despite the welcome discovery of the larger than expected number of Irrawaddy dolphins off Bangladesh, Smith of the Wildlife Conservation Society said their long-term future was far from secure.