One of the world's largest crocodilian species is also its rarest. With just a few hundred individuals left, the critically endangered gharial (Gavialis gangeticus) faces an uncertain future in its remaining river habitats in India and Nepal.

Once common, gharials were hunted into near extinction for their skins in the early 20th century. Since then, captive-bred gharials have been released into rivers by the hundreds, but survival rates have been low, probably because so little was known about the species.

Last year, more than 100 gharials mysteriously died in India. While the cause of death has never been conclusively proven, scientists at the time hypothesized that they died of gout (a buildup of uric acid, a waste product), brought on by kidney failure, which itself was brought on by exposure to toxic chemicals in India's polluted rivers.

Now, scientists in Nepal  are trying to find out as much information as possible about their country's gharials so they can devise a plan to keep this increasingly rare species from disappearing forever.

The project started a few weeks ago, when Nepal's Department of National Parks and Wildlife Conservation, in collaboration with WWF Nepal, attached RFID tags to 14 gharials and re-released them in the Rapti River. The project,  set to run through December, will gather information about gharial habitats and behavior, says Rinjan Shrestha, a WWF Nepal conservation biologist.

Shrestha says that "habitat degradation, overfishing and water pollution" are the main reasons for gharial decline in Nepal.

"The radio tags are used to locate the position of the released gharials," says Shrestha. Once located, the monitoring crew will record the gharials' GPS positions. "We have to localize every tag manually, with a directional antenna," says Antoine Cadi, a project manager at Awely, an environmental NGO in France, who is providing technical assistance for the program. "This method is less expensive than satellite tracking and gives us the opportunity to follow the behavior of the crocs."

The team will try to locate the gharials daily until July, when monsoon season begins, "then do our best during the raining period," Cadi says, noting that researchers will step up efforts again in September to gauge the impact of monsoon flooding on the shrinking population.

Cadi believes that monsoon season may drive gharials from Nepal's cleaner rivers into India, where they could face greater threats. "Every day they are pushed down the river... and, after some months, they can not avoid crossing the dam," he says, "and finally arriving in India, where all the threats known in Nepal are more important and strong."

Image: © Sanjib Chaudhary/WWF Nepal. Used with permission.