Status of the Ganges river dolphin or shushuk Platanista gangetica in Kaptai Lake and the southern rivers of Bangladesh

Surveys for shushuks Platanista gangetica were conducted during January to April 1999 in Kaptai Lake and the southern rivers of Bangladesh. A populati on of at least 125 dolphins was recorded in the Karnaphuli and Sangu rivers and connecting canal. The overall encounter rate was 0.76 dolphins per km. Density was highest in the lower reaches of the Sangu, where we recorded 1 .36 dolphins per km. These rates are fairly high when compared with other a reas of shushuk distribution. Dolphin movements in the Sikalbaha-Chandkhali Canal were consistent with it being used as a corridor for migration and d ispersal between the Karnaphuli and Sangu. Shushuks were also sighted in ma rine waters of the Karnaphuli and Sangu river mouths, adding credibility to the hypothesis that dolphins move along the coast between the Ganges-Brahm aputra-Meghna and Karnaphuli-Sangu systems, perhaps during the monsoon when freshwater plumes extend into the Bay of Bengal. No dolphins were observed in Kaptai Lake, a dam-created reservoir of the upper Karnaphuli, despite r eports of occasional sightings by local fishermen. No shushuks were observe d in the Bagkhali and Matamuhuri rivers, possibly because of seasonal-closu re dams present near the mouths of both rivers. The main threats to dolphin survival in the Karnaphuli-Sangu system are probably accidental entangleme nt in monofilament gillnets, bioaccumulation of persistent contaminants and possibly collisions with motorized vessels and a decline in prey as a resu lt of over fishing. The most significant conservation measure that could be taken would be to establish a protected area for dolphins in the Sangu Riv er below the Dohazari Bridge.