Since 2003, the population has sustained 88 deaths, of which more than 60% were calves less than two weeks old. Researchers found toxic levels of pesticides such as DDT and environmental contaminants such as PCBs during analysis of the dead calves’ bodies. Because human populations living along the Mekong consume the same fish and water as the dolphins, WWF said, these pollutants may pose a health risk to them as well.
“Analysis identified a bacterial disease as the cause of many of the calf deaths,” said Rob Shore, WWF-UK freshwater programmes manager. “This disease would not be fatal unless the dolphins’ 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 investigating the source of the contaminants. Its report, Mortality Investigation of the Mekong Irrawaddy River Dolphin in Cambodia, found high levels of mercury also were present in some of the dead dolphins. Mercury, suspected to be from gold-mining activities, directly affects the immune system. Limited genetic diversity due to inbreeding is likely to be another factor in the calf deaths, and adult dolphins also are threatened by hydropower development and accidental capture in fishermen’s nets.
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