DDT & PCBs Killing Near Extinct Dolphins

From World Wildlife Federation:

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.

Irrwaddy Dolphin WWF Photo

Irrawaddy Dolphin WWF Photo

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.

Abouth the Irrawaddy Dolphin

The species is patchily distributed in South-East Asia, and is primarily found in estuaries and mangrove areas, with freshwater populations occurring in river systems.

The Mahakam river (Kalimantan, Indonesian Borneo) population of Irrawaddy dolphins is severely threatened by fisheries bycatch and habitat degradation, and may number as few as 34 animals.

Surveys conducted in 2001 estimated that the Malampaya Sound population in the Philippines consists of just 77 individuals, confined to a small area in the inner sound, and is the only known population of this species in the country.

During 2001 there were reports that as many as five animals from this population were killed incidentally in fishing operations, indicating that the Irrawaddy dolphins of Malampaya Sound are in immediate danger of extinction due to low numbers, limited range, and high mortality.

The Mekong River Irrawaddy dolphin (Orcaella brevirostris) population inhabits a 190km stretch of the Mekong River between Cambodia and Lao PDR. The latest population is estimated between 64 and 76 members (2008 figures).

Physical Description

The Irrawaddy dolphin is identified by a bulging forehead, a short beak, and 12-19 teeth on each side of each jaw. The pectoral fin is broadly triangular. There is a small dorsal fin, on the posterior end of the back.

When diving, this dolphin breathes at intervals of 70-150 seconds; the head appears first and then disappears, and then the back emerges, but the tail is rarely seen.

Head and body length is 180-275 cm.

Irrawaddy dophins are slaty blue to slaty gray throughout, with the underparts slightly paler.


Biogeographic realm

Range States
Australia, Papua New Guinea, Indonesia, India, Thailand, Myanmar, Laos, Cambodia, Vietnam, Philippines

Geographical Location
South-East Asia

Interesting Facts

Reports from the 1970s show that the fishermen of Burma attract the Irrawaddy dolphin by tapping the sides of their boats with oars. By swimming around the boat, the dolphin brings the fish into nets, and the fishermen share their catch with it.

Categories: Dolphins, Rivers to the Sea

Tags: , , ,

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