Mekong dolphins on the brink of extinction

The Mekong River Irrawaddy dolphin (Orcaella brevirostris) population inhabits a 190km stretch of the Mekong River between Cambodia and Lao PDR. Since 2003, the population has suffered 88 deaths of which over 60 percent were calves under two weeks old. The latest population is estimated between 64 and 76 members.

“Necropsy analysis identified a bacterial disease as the cause of the calf deaths. This disease would not be fatal unless the dolphin’s immune systems were suppressed, as they were in these cases, by environmental contaminants,” said Dr Verné Dove, report author and veterinarian with WWF Cambodia.

Researchers found toxic levels of pesticides such as DDT and environmental contaminants such as PCBs during analysis of the dead dolphin calves. These pollutants may also pose a health risk to human populations living along the Mekong that consume the same fish and water as the dolphins.

“These pollutants are widely distributed in the environment and so the source of this pollution may involve several countries through which the Mekong River flows. WWF Cambodia is currently investigating the source of the environmental contaminants,” said Dr Dove.

High levels of mercury were also found in some of the dead dolphins. Mercury, suspected to be from gold mining activities, directly affects the immune system making the animals more susceptible to infectious disease.

“A trans-boundary preventative health programme is urgently needed to manage the disease affected animals in order to reduce the number of deaths each year,” said Seng Teak, Country Director of WWF Cambodia.

Limited genetic diversity due to inbreeding was another factor in the dolphin deaths.

“The Mekong River dolphins are isolated from other members of their species and they need our help. Science has shown that if the habitat of cetaceans is protected then populations can show remarkable resilience,” said Mr Teak.

The Mekong River Irrawaddy dolphin has been listed as critically endangered on the IUCN Red List of Threatened Species since 2004.