BANGKOK — Pollution on the Mekong River is putting the rare Irrawaddy dolphins in danger of disappearing from Cambodia and Laos, according to a study released today by an environmental group.
The World Wide Fund For Nature Cambodia said that it has documented 88 deaths in the past six years of the Irrawaddy dolphin or Orcaella brevirostris along a 118-mile stretch of the Mekong River.
The population in the Mekong is now believed to include as few as 64 members, it said, down from 80 to 100 just three years ago.
Researchers from WWF Cambodia said they found toxic levels of pesticides such as DDT and environmental contaminants such as PCBs during an analysis of dead dolphin calves. They also found mercury in some dead dolphins, a toxin used in gold mining that can compromise the immune system of marine animals.
The group said it was investigating the source of the pollutants, noting that many young calfs died of bacterial diseases that would not normally be fatal unless their immune systems were compromised 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,” according to Verne Dove, the report’s author and veterinarian with WWF Cambodia.
The Irrawaddy dolphin, which is related to orcas or killer whales, grows to up to 8 feet in length and frequents large rivers, estuaries, and freshwater lagoons in south and southeast Asia.
Scientists do not know exactly how many Irrawaddy dolphins remain in the world — researchers recently found a population of nearly 6,000 near Bangladesh’s mangrove forests — but the species is listed as “vulnerable” on the IUCN Red List of Threatened Species. The Mekong River subpopulation has been listed as “critically endangered” since 2004.
Seng Teak, WWF Cambodia’s country director, urged Mekong River countries to develop a coordinated program to protect the dolphins.
“The Mekong River dolphins are isolated from other members of their species and they need our help,” he said in a statement. “Science has shown that if the habitat of cetaceans is protected, then populations can show remarkable resilience.”
Brian Smith, an Irrawaddy dolphin expert with the Wildlife Conservation Society, said the findings were surprising given that until now, the biggest threat facing the dolphins was fishing. He cautioned more research was needed to be done to establish a link between the deaths and pollution.
“Although pollution is generally included in the laundry list of threats facing these animals, it has generally been assumed to be of lesser importance compared to other threats, especially fisheries interactions,” Smith said in an e-mail interview.
However, he said the extremely low survivorship of calves on the Mekong — and the fact that many carcasses were found with lesions — suggests that disease combined with pollutants documented in the WWF study “may indeed be an important factor threatening the population.”
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