A 200kg Irrawaddy dolphin was found dead at the border between Stung Treng province and Laos, bringing the dolphin death toll for 2015 to five, authorities said yesterday.

Villagers in Koh La Ngor, in Preah Rom Kel commune, discovered the carcass on April 1, according to Dieb Bora, provincial deputy chief of fisheries in Stung Treng.

“We were surprised when it was found dead like this,” he said, explaining that the cause of death appeared to be old age rather than illegal poaching or explosives used in fishing, as the body was devoid of bruises or wounds.

The female Irrawaddy dolphin found last week is thought to be one of the largest and oldest in the region, measuring almost 2.5 metres, and was likely 26 to 30 years old, Bora said. The age was determined by the minimal teeth that remained in the animal’s mouth – only two, while a mature dolphin will have between 60 and 62.

Last week, the dolphin’s body was brought to shore where four monks waited to bless the body in a funeral ceremony.

The dolphin was one of just six estimated to be in that stretch of the Mekong, and is one of 28 to have died since 2011, according to the conservation group WWF. Just seven were born last year, and one more calf has been born in 2015.

The death occurred just two weeks after WWF voiced concerns over the high rate of death for the species, especially during the dry season when water levels fall. With just 85 Irrawaddy dolphins believed to remain in the Mekong, the rare creatures have become an important part of the tourist industry in the region.

The body was taken to the WWF office, where a full autopsy will be conducted, said Un Chakrey, WWF Cambodia’s press officer.

Chhit Sam Ath, director of WWF Cambodia, expressed his sadness for the death and appealed to the community to preserve the rest of the population and reinforce poaching laws.