Huge Population Of Rare Dolphins Discovered

Using rigorous scientific techniques, WCS researchers estimate that nearly 6,000 Irrawaddy dolphins, which 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—an area where little marine mammal research has taken place up to this point. Prior to this study, the largest known populations of Irrawaddy dolphins numbered in the low hundreds or less.

Each discovery of Irrawaddy dolphins is important because scientists do not know how many remain on the planet. In 2008, they were listed as vulnerable in the IUCN Red List based on population declines in known populations.

The results of the study were announced today at the First International Conference on Marine Mammal Protected Areas in Maui, Hawaii and published in the Winter issue of the Journal of Cetacean Research and Management. Authors of the study include Brian D. Smith, Rubaiyat Mansur Mowgli, and Samantha Strindberg of the Wildlife Conservation Society, along with Benazir Ahmed of Chittagong University in Bangladesh.

“With all the news about freshwater environments and state of the Oceans, WCS’s discovery that a thriving population of Irrawaddy dolphins exists in Bangladesh gives us hope for protecting this and other endangered species and their important habitats,” said Dr. Steven E. Sanderson, President and CEO of the Wildlife Conservation Society. “WCS is committed to conservation of these iconic marine species from dolphins, sea turtles, sharks to the largest whales.”

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

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 a second paper, published in the March/April issue of 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. The recent likely extinction of the Yangtze River dolphin, or baiji, is a potent reminder of how vulnerable freshwater dolphins are to extinction via the impacts of humans.

The Irrawaddy dolphin grows to some 2 to 2.5 meters in length (6.5 to 8 feet) 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.

WCS is currently working closely with the Ministry of Environment and Forests in Bangladesh on plans for establishing a protected area network for both Irrawaddy and Ganges River dolphins in the Sundarbans mangrove forest. Funding is critical to sustaining these activities along with WCS’s long-term efforts to study the effects of climate change on this habitat, support sustainable fishing practices, and develop local ecotourism projects.

Support for this study has been provided in part by the Kerzner Marine Foundation and Ocean Park Conservation Foundation, Hong Kong (OPCFHK). This study was also funded in part by the U.S. Marine Mammal Commission. The Convention on Migratory Species of Wild Animals (CMS) has also supported WCS efforts as part of a regional program for cetacean conservation in the Bay of Bengal.