Dolphin Discovery

April 1, 2009

Nearly 6,000 Irrawaddy dolphins are alive and swimming in Bangladesh, according to new WCS research. Prior to this study, the largest known populations of Irrawaddy dolphins numbered in the low hundreds or less.

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.

Prior to this study, little marine mammal research had taken place in the Sundarbans—which translates to “beautiful jungle” in Bengali. Researchers had pegged the largest Irrawaddy dolphin populations in the low hundreds or fewer. In 2008, the species was listed as vulnerable on the IUCN Red List.

“This discovery gives us great hope that there is a future for Irrawaddy dolphins,” said WCS researcher Brian D. Smith, who led the study. “Bangladesh clearly serves as an important sanctuary for Irrawaddy dolphins, and conservation in this region should be a top priority.”

Despite his optimism, however, Smith and other researchers warn that the dolphins are facing increasing threats to their survival. During the study, they encountered two that had drowned after becoming entangled in fishing nets. Local fishermen say this is a common occurrence. The scientists also found that the dolphins must cope with declining freshwater supplies, caused by upstream water diversion in India coupled with sea-level rise. The latter issue has been brought on by climate change. WCS researchers are currently studying the long-term effects of this phenomenon.

These circumstances also threaten the endangered Ganges River dolphin, which shares part of its range in the Sundarbans with the Irrawaddy dolphin. The recent likely extinction of the Yangtze River dolphin, or baiji, is a potent reminder of how vulnerable freshwater dolphins are to human impacts on the environment.

Irrawaddy dolphins are related to orcas, also known as killer whales. The dolphins grow up to 8 feet long and frequent large rivers, estuaries, and freshwater lagoons in South and Southeast Asia. In Myanmar’s Ayeyarwady River, these dolphins are known to cooperatively fish with humans, helping to herd schools of fish toward boats and awaiting nets. The practice benefits the fishermen—increasing the size of their catches up to threefold—as well as the dolphins, which fill their own bellies with some of the cornered fish and those that fall out of the fishing nets.

In 2006, WCS helped establish a protected area along the Ayeyarwady River to conserve this critically endangered marine mammal population. Currently, conservationists are working closely with the Ministry of Environment and Forests in Bangladesh on plans for establishing a protected area network for the dolphins in the Sundarbans. WCS is also supporting sustainable fishing practices and helping to develop local ecotourism projects that benefit the region’s people and wildlife.

Support for this study has been provided in part by the Kerzner Marine Foundation and Ocean Park Conservation Foundation, Hong Kong; the U.S. Marine Mammal Commission; and the Convention on Migratory Species of Wild Animals, which operates a regional program for cetacean conservation in the Bay of Bengal.


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