A dozen Irrawaddy dolphins have been found dead in the sea off the eastern coast of Thailand since last month. The deaths of the aquatic mammals were feared to have been caused by sudden lack of oxygen.

Villagers of Trat province found the dolphins floating dead in the sea of the Gulf of Thailand and hauled them over to shore in Klong Yai district. Four of the dozen fish were spotted dead in the sea off the coastal district so far this week.

Kritapat Srisangkajorn, a local Save-the-Dolphins activist, said on Thursday the Irrawaddy dolphins were believed to have been trapped by fishing nets from seagoing trawlers, denying them the chance to escape and swim onto the surfaces of the sea to breathe.

The deaths of the critically endangered dolphins were said to have resulted from their failures to inhale, he said. Unlike other species of fish, dolphins and whales need to come up onto the surfaces of the sea to inhale.

Some of the two-meter-long fish were found floating dead and brought to shore by the villagers while others were found lying dead on the beaches, believed to have died in the sea a few days earlier.

A group of American researchers of the University of San Francisco working on rare aquatic creatures had alerted the Klong Yai villagers on the fatal perils being allegedly caused to the Irrawaddy dolphins by fishing trawlers in the Gulf of Thailand, Kritapat said.

"The authorities are bound to take urgent measures to stop the continual losses of the Irrawaddy dolphins off Trat province. But they haven't done enough to help save the dolphins as yet," commented the Save-the-Dolphins activist, adding that more of the fish were feared to die that way.

The number of the critically endangered dolphins in the Gulf of Thailand was reported to be currently less than 50. Following the deaths of the dozen in the Gulf area so far, the rest might possibly be on the verge of extinction, if they could not find a very safe sanctuary elsewhere, according to the activist.

An estimated 7,000 Irrawaddy dolphins were reported in all waters of the world, mostly in the Bay of Bengal off Bangladesh, the Andaman Sea and the South China Sea.

Brackish waters of Mekong River in Laos and Cambodia are also known as a habitat for the dolphins.