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Title
Review of the conservation status and protected areas for Ganges River Dolphins Platanista Gangetica and Irrawaddy Dolphins Orcaella Brevirostris in the river systems of Bangladesh
Author(s)
Smith, B.D.;Ahmed, B.;Alom, Z.;Ahmad, I.U.;Mowgli, R.M.;Mansur, E.F.
Published
2010
Abstract
Little information is available on the range-wide status of the Ganges River dolphin in Bangladesh but anecdotal reports and personal observations suggest that the species is still fairly widespread in most major rivers and their tributaries. Sighting rates include 0.13 groups/km (mean group size = 1.8) in the Jamuna River, 0.08 groups/km (mean group size = 3.8) in the Kushiyara River, and 0.76 dolphins/km in the Karnaphuli and Sangu system in southeast Bangladesh, with a higher encounter rate of 1.36 dolphins/km recorded in the lower Sangu. The status of freshwater dolphins is best known in the Sundarbans mangrove forest where a Huggins conditional likelihood model of concurrent counts made by independent teams generated population estimates of 225 Ganges River dolphins (CV = 12.7%) and 451 Irrawaddy dolphins (CV = 9.6%). Fisheries interactions represent the greatest immediate threat to freshwater dolphins in Bangladesh. Directed hunting of Ganges River dolphins for their oil has been reported to supply oil for medicinal purposes and as a fish attractant. A large proportion of the dolphin carcasses used for oil are obtained from animals that become entangled in nylon gillnets and are then killed by local fishermen. Riverine and estuarine waters in Bangladesh are already experiencing the ecological impacts of declining freshwater supplies and climate change. The dependence of Ganges and Irrawaddy dolphins on abundant freshwater flow makes them particularly vulnerable to habitat loss due to upstream water abstraction and sea-level rise. Three waterway segments have been identified in the Sundarbans for focal protection using a “hotspot” scoring system of encounter rates recorded by captains of three nature tourism vessels. A proposed protected area network including these segments will provide a platform for understanding the ecological effects of declining freshwater supplies and climate change and a basis for developing adaptive management responses that benefit both fishermen and freshwater dolphins. The proposed network in the Sundarbans covers only a small fraction of the total freshwater dolphin habitat in Bangladesh. A priority area for future consideration as a protected area is the lower Sangu River.
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PUB14764