The most recent population survey of Cambodia’s Irrawaddy dolphins shows the dwindling species – its youngest generation in particular – remains imperiled.

After almost 140 hours of dolphin-spotting on the Mekong River from Kratie to the Lao border, researchers estimate 71 dolphins survive, although the population could range from 66 to 86, according to the global conservation group WWF.

The survey – carried out during the dry months of April and May 2007, when the river level drops and the dolphins are concentrated in nine deep pools – counted markedly fewer specimens than a 2005 study that estimated a population of 108 to 146.

Both high mortality and a new, more accurate survey methodology could account for the drop-off, according to Richard Zanre, WWF’s Freshwater Conservation Program Manager.

“The good news is adult mortality has reduced over the last five or six years,” Zanre said.

He credited government and NGO efforts to curb the use of gill nets in the core habitat, including an official ban instituted last year and alternative livelihood programs for fishermen in the area.

The nets are believed to have snared and drowned a significant number of the nearly 80 dolphins found dead in the past five years.

“But the big concern is the calf mortality remaining high,” Zanre added. “We are also seeing what seems to be a drop in the birth rate.”

The exact cause remains a troubling unknown. Results from autopsies conducted on the tissue of dead calves have recently returned from laboratories in Canada and the US. They await analysis.

Additionally, tests will be run on water samples to learn whether sewage, agricultural or industrial run-off could be hindering reproduction.

Another threat looms upstream, where the Lao government recently approved construction of a hydroelectric dam above the Khone Falls on the Laos-Cambodia border, Zanre said.

Cambodia’s Irrawaddy dolphins, which range from Kratie to Southern Laos, are one of only three populations still in existence. The others survive in Myanmar and Indonesia.

The International Union for the Conservation of Nature has listed Cambodia’s dolphins as Critically Endangered since 2004.