Researchers with a wildlife conservation group say they have discovered thousands of rare Irrawaddy dolphins living in the waters of Bangladesh.

Authors of a study say they found nearly 6,000 of the endangered freshwater animals in the Sundarbans mangrove forest and in the adjacent waters of the Bay of Bengal.

Wildlife protection agencies say before the study, only small populations of Irrawaddy dolphins were known to exist, numbering fewer than 200.  

The scientists began counting the dolphins in 2004.

The results were released Wednesday at a marine wildlife conference in Hawaii, and published in the Journal of Cetacean Research and Management.

The lead researcher, Brian Smith of the New York-based Wildlife Conservation Society, said the find "gives us great hope that there is a future for Irrawaddy dolphins."

In a statement from the conservation group, he said Bangladesh is an important sanctuary for the endangered mammals, and "conservation in this region should be a top priority."

Smith warns that even the large population of the dolphins in Bangladesh is being threatened by entanglement in fishing nets, as well as by threats to its freshwater habitat posed by global warming.

Irrawaddy dolphins can grow to up to 2.5 meters in length and live in several waterways in southeast Asia.  The animals were declared a threatened species last year by the International Union for Conservation of Nature and Natural Resources (IUCN).

In addition to Smith, the study's other authors include scientists Benazir Ahmed from the Chittagong University zoology department and Rubaiyat Mansur Mowgli from a Bangladeshi whale and dolphin research program.

Some information for this report was provided by AP.