6,000 Rare Dolphins Found in South Asia

A huge population of rare dolphins threatened by climate change and fishing nets has been discovered in South Asia.

WCS researchers have discovered a stronghold for one of the world’s rarest freshwater dolphins, the Irrawaddy, deep in the waterlogged jungles of Bangladesh. The scientists counted nearly 6,000 of the dolphins in the South Asian country’s Sundarbans mangrove forest and the adjacent waters of the Bay of Bengal.

Researchers with the Wildlife Conservation Society estimate that nearly 6,000 Irrawaddy dolphins, marine mammals that are related to orcas or killer whales, were found living in freshwater regions of Bangladesh’s Sundarbans mangrove forest and adjacent waters of the Bay of Bengal.

In 2008, they were listed as vulnerable in the IUCN Red List based on population declines in known dolphin populations.

Despite finding this extraordinarily large population, the study’s authors warn that the dolphins are becoming increasingly threatened by accidental entanglement in fishing nets. During the study, researchers encountered two dolphins that had become entangled and subsequently drowned in fishing nets — a common occurrence according to local fishermen.

In another study, detailed in the March/April issue of the journal Aquatic Conservation: Marine and Freshwater Ecosystem, Smith and his coauthors report the additional long-term threat to the dolphin population of declining freshwater supplies, caused by upstream water diversion in India, coupled with sea-level rise due to climate change.

These circumstances also threaten Ganges River dolphins, an endangered species with a range that overlaps with that of the Irrawaddy dolphins in the Sundarbans mangrove forest. Yangtze River dolphin, or baiji, are a type of freshwater dolphin thought to be extinct due to the impact of humans.

The Irrawaddy dolphin grows to some 6.5 to 8 feet (2 to 2.5 meters) in length and frequents large rivers, estuaries, and freshwater lagoons in South and Southeast Asia.

In Myanmar’s Ayeyarwady River, these dolphins are known for “cooperative fishing” with humans, where the animals voluntarily herd schools of fish toward fishing boats and awaiting nets. With the aid of dolphins, fishermen can increase the size of their catches up to threefold. The dolphins appear to benefit from this relationship by easily preying on the cornered fish and those that fall out of the net as the fishermen pull it from the water.

In 2006, WCS helped establish a protected area along the Ayeyarwady River to conserve this critically endangered mammal population. The WCS is working on establishing a similar protected area network for both Irrawaddy and Ganges River dolphins in the Sundarbans mangrove forest.

Funding for the new study was provided in part by the Kerzner Marine Foundation and Ocean Park Conservation Foundation, Hong Kong (OPCFHK), and the U.S. Marine Mammal Commission.

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