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The Mekong River Irrawaddy dolphin (Orcaella brevirostris) population inhabits a 190km stretch of the Mekong River between Cambodia and Laos. 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 individuals.
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.
Rob Shore, WWF-UK freshwater programmes manager, said: Analysis identified a bacterial disease as the cause of many 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.
"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 is currently investigating the source of the environmental contaminants."
The report, Mortality Investigation of the Mekong Irrawaddy River Dolphin in Cambodia, found high levels of mercury were also present 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 is likely to be another factor in the calf deaths, and adult dolphins are also threatened by hydropower development and accidental capture in fishermen's nets.  
"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," added Mr Teak.
The Mekong River Irrawaddy dolphin has been listed as critically endangered on the IUCN Red List of Threatened Species since 2004.
Editor's notes:
The way we live in the UK is leading to environmental threats such as climate change, species extinction, deforestation, water shortages and the collapse of fisheries. WWF's One Planet Future Campaign is working to help people live a good quality of life within the earth's capacity. For more information visit to download:

  • The dolphin necropsy report in Khmer and English
  • Broadcast quality footage of the dolphins swimming the Mekong River at Cambodia. download:

  • High quality photos of the dolphins playing in the Mekong River in Cambodia.

WWF is working to conserve 600,000km2 of the world's most biologically diverse, economically viable and seriously threatened forests and rivers within the Greater Mekong, home and life source to over 300 million people in Cambodia, China, Laos, Myanmar, Thailand, and Vietnam.
The Mekong River Irrawaddy dolphin is regarded as a sacred animal by both Khmer and Lao people, and is an important source of income and jobs for communities involved in dolphin-watching ecotourism initiatives.
More than 60 million people in the lower Mekong basin depend on the river system for food, transport and economic activity. The Mekong River produces an estimated 2.5 million tons of fish per year, with a value of at least US$2 billion, making it the largest inland fisheries in the world. Eighty percent of the animal protein for Mekong inhabitants comes from the Mekong, with 70 percent of the commercial catch being long distance migrant species.
For more information contact:
Robin Clegg, Senior Press Officer, WWF-UK, t: 07771 818707, e: