Conservation officers with a Dugong found dead on a Sri Lankan beach. Ocean Research & Conservation Association.

Once a moving object of roughly a dugong's size - an adult dugong measures up to three meters - is detected, the team sends underwater divers, or a drone, which is essentially a flying camera, to verify it.

"It's impossible to send the divers during the monsoon season when the sea gets choppy," Weerakkody says. "As to the drone, we have adapted one that was once used for filming weddings. We would like to have a more advanced one, one used for military purposes, for example. But that would be simply beyond our means at this stage."

The drone, bought with project money, usually flies to a height of 500 meters. When the sea is clear it can film objects lying as deep as five meters underwater.

"But sometimes, dugongs can be staying somewhere deeper in the ocean - ten meters underwater maybe - and that would be hard for us," says Weerakkody, who, when asked, says he would also love to have an underwater drone.

Both the sonar and the drone can also be used for mapping sea grass meadows.

Peiris says that most of the time a dead dugong will end up in some black market in Sri Lanka where, weighing between 250 kg and 400 kg, it is chopped up and sold, possibly to local restaurants.

In fact in the early 20th century there was a fishery for dugong in Sri Lanka. One hundred to one hundred fifty dugongs were taken annually in the Mannar Gulf in the 1950s. The Sri Lanka Civil War, fought between 1983 and 2009, meant that the surrounding waters were closed off for three decades. The end of that war was welcomed by animal protectionists with mixed feelings.

"These days thousands of fishing boats that use bottom trawling pass by the same water over one night," Suraweera says.

"With its long life span of 70 years or more, and slow rate of reproduction, the dugong as a species is especially vulnerable to extinction. I've seen dugong bodies - adults' and babies'. I hope that one day I can see a live dugong, and that would be lovely."