the conservation action plan the ganges river dolphin - IUCN SSC ...

IrrigationExcess extraction of the river water forirrigation has lowered water levelsthroughout the species range and hasthreatened suitable habitat in the Ganges.The long-term implications of the reductionof dry-season flow in the Ganges arecatastrophic for the survival of 'susus'.The total measured flow of suspended sedimentin the tributaries to the Ganga River is 488 x10 6 t/yr, while the quantity of sediment movingin the Ganga at Farakka is 729x10 6 t/yr ofwhich 328x10 6 t/yr is transported down theHooghly River (Wasson, 2003).The River Kosi, one of the major tributaries ofthe Ganga, carries maximum silt load in theGanga system with average annual suspendedload to the tune of 2774 tonnes/km 2 which isthe second highest for any river of the world.The Huang River carries the highest load of2804 tonnes/km 2 (IUCN 1980).Riverine resource extractionDredging and development of the riverenvironment has altered its nature andeliminated counter currents, one of the mostpreferred habitats of the dolphin.Increasingly heavy river traffic in the Gangesand Brahmaputra may result in habitatrestriction, noise pollution, depletion of preybase and changes in feeding behavior of the'susus' in the rivers. Other sources of habitatdegradation include the removal of stones,sand (Mohan et al. 1997) and woody debris(Smith, 1993). These activities threaten theecological integrity of the riverineenvironment, especially in small tributarieswhere suitable habitat is more confined andtherefore more vulnerable to local sources ofdegradation.SedimentationDue to loss of vegetation cover in thecatchment area and in floodplains, theincreasing rates of sedimentation cause a riseof the river bed, reducing the river's waterretaining capacity. Sedimentation has a directimpact on the physical and biologicalcharacteristics of the river basin. It affects theother river biota, including fish, reducing theprey base of the dolphin. High altitudegrazing, forest management, limitedcultivation, and road building in themountain ranges from where these riversoriginate are the prime factors influencingsedimentation (Wasson, 2003). The RiverGanges receives sediments from Himalayasas well as the peninsular regionPollutionThe concentrations of fertilizer and pesticideresidues, and industrial and domesticeffluents are very high in the Ganges River.The effects of such pollutants may bedeleterious to dolphin populations, andpollutant loads are expected to increase withindustrialisation and the spread of intensivemodern agricultural practices (Smith andReeves 2000a).About 1.5 million metric tons of chemicalfertilizers and about 21,000 tons of technicalgrade pesticides are dumped annually to theGanges-Brahamaputra river system in Indiain 2002-2003. Concentrations ofpolychlorinated biphenyls (PCBs),hexachlorocyclohexane (HCH), chlordanecompounds, and hexachlorobenzene (HCB)in the Ganges River dolphin blubber, muscle,kidney, liver and prey collected from stomachof the dolphins collected during 1993through 1996 from the River Ganges in andaround Patna, India were determined bySenthilkumar et al., (1999). The studycompared the organochlorine concentrationswith values reported for samples analysedduring 1988 through 1992 and suggestedthat the contamination by these compoundshas increased in the river. Kannan et al.,(1997) determined concentrations of butyl-16