CURRENT STATUS OF THE GANGES RIVER DOLPHIN, PLATANISTA GANGETICA IN THE RIVERS KOSI AND SON, BIHAR, INDIA' (With one text-figure) R.K. SINHA' AND GOPALSHARMA~ Key words: Platanista gangetica, population, threats, conservation, River Kosi, River Son, Bihar Surveys were conducted in February and March, 2001 to assess the current status of the Ganges river dolphin in the Rivers Son and the Kosi. No dolphin was sighted in the entire stretch of about 300 km of the Son, in Bihar. The local fishermen reported total elimination of dolphin population in c. 100 km stretch of the Son from the Uttar Pradesh - Bihar border to the Son Barrage at Indrapuri. During monsoon, the dolphins migrate for about 200 km from the mainstem of the Ganges into the Son up to the barrage. Dolphins were sighted in the entire stretch of about 300 km of Kosi between the Kosi Barrage at the Indo-Nepal border and its mouth at Kursela in Bihar. A total of 87 dolphins were sighted in the Kosi during the survey, however, many must have been missed due to the highly braided channel of the river. In both the rivers, no apparent source of pollution was found. Siltation and construction of the barrage were observed to be the main cause of habitat degradation in both the rivers. only freshwater dolphin species found in the world. Obligate river dolphins live only in fresh The Ganges river dolphin Platanista water, their physiological and ecological gangetica, commonly known as susu, is requirements apparently make it impossible for distributed in the Ganga-Brahmaputra-Meghna them to live in marine waters. and Karnaphuli-Sangu river systems of India, Other small cetaceans are normally Nepal and Bangladesh, between the foothills of associated with the marine environment, but they the Himalaya and the estuarine zone. do range far upstream in large Asian rivers. All the three Asian species of freshwater These include, the finless porpoise dolphins are classified as Endangered or (Neophocaena phocaenoides) in the Yangtze Critically Endangered. Listed in order of most river of China, and Irrawaddy river dolphin to least threatened, are baiji (Lipotes vexillfer) Orcaella brevirostris in the Ayeyarwady in River Yangtze of China (population: a few (formerly Irrawaddy) river of Myanmar, tens), bhulan (Platanista minor) in River Indus Mahakam river of Indonesia, and Mekong River of Pakistan (population: a few hundreds), and of Lao P.D.R., Cambodia, and Vietnam. Sotalia susu (Platanista gangetica), population about fluviatilis is another such species found in the 2,500. The fourth freshwater species, boto (Znia Amazon-Orinoco river systems of South geoffrensis) is found in the Amazon River System America. in South America, population of which is The freshwater dolphins have a longer estimated to be about 5,000. These four are the snout than marine species, which probably help them in collecting their food in the mud bottom Accepted August, 2001 of rivers. The two species of genus Platanista 2Environrnental Biology Laboratory, Department ofzoology, Patna University, found in the Ganga and Indus system are Patna 800 005, Bihar, India. practically blind, as they have eyes without 'Ernail: [email protected] crystalline lenses (Herald et al. 1969) and the JOURNAL, BOMBAY NATURAL HISTORY SOCIETY 100(1), APR. 2003 27 CURRENTSTATUS OF THE GANGESRIVER DOLPHIN IN THE RIVERSKOSIAND SON transparency of their cornea is limited as it is above the bottom. The flippers are thought to vascuiarised (Dawson 1980). While visual acuity have an important tactile function. Shortly before is reduced in these species, they may be able to surfacing, the dolphins reverse the spin back to form crude images using the narrow aperture of the direction in which the dive began. the pupil in a manner analogous to a pinhole In the Karnali river of Nepal, in their far camera. Amazon and Yangtze river dolphins upstream range as well as in the mainstem of have very limited vision. the Ganga, su,su are found most often in 'primary Evolutionary adaptation to a fluviatile habitats' where convergent streams create an environment has resulted in a regression of the eddy counter-current system in the mainstream eye and the development of a sophisticated flow (Smith 1993). Less often, the dolphins are echolocation system, which allows Odontocetes, found in "marginal habitats" where the river the suborder of toothed whales, to 'see' their meanders and creates similar eddy counter- environment through sound. Pulsed vocalization current systems, which are also areas of high produced in specialized air sinuses in the nasal human use, making them particularly vulnerable passages is focused by the 'melon' (forehead), to local environmental disturbances. which functions as an acoustic lens. The reflected The river dolphin often takes advantage pulsed sounds are received back through the of the ecotone created by the transition between jawbone, transmitted to the middle ear, and then scour pools and running waters, visible as eddy analysed by the comparatively large brain. turbulence. They prey on species migrating along Although the meta-population of the susu the mainstem, while monitoring foraging totals over two thousand, isolated subpopulations, opportunities from within the hydraulic refuge especially in Nepal and in the Karnaphuli-Sangu of counter-currents. River System of Bangladesh, have become extinct or critically reduced by the barrier effects of dams Current Status of the Ganges river dolphin and barrages (Haque 1976, Smith et al. 1994). The total population of the suszi was The distribution range of susu is shrinking, as roughly estimated to be only 4,000-5,000 (Jones evinced by their elimination from many of the 1982). Dolphins are sighted throughout the smaller tributaries and upper reaches of the Ganga from the Middle Ganga Barrage, Bijnor Ganga, where they were found earlier. Their (129 km downstream of Haridwar) to its mouth population in the mainstem of the larger rivers at Sagar Island in the Bay of Bengal. About is declining as they are being killed both 35 susus have been isolated between the two incidentally as well as directly. Also, they barrages at Bijnor and Narora (1 66 km) in Uttar compete unsuccessfully with humans for Pradesh (Sinha et al. 2000). The population shrinking water and prey resources, The IUCN between Narora and Allahabad (about 500 km) recently changed the status of the species from in low water season (January-March) is very Vulnerable to Endangered (Baillie and sparse (a few tens) (Sinha 1999). In the lower Groombridge 1996). reaches of the Ganga in West Bengal, only Dolphins swim almost constantly on their 152 susus were sighted in the Bhagirathi- side. Shortly after a dive, they spin 90' on their Hooghly river system below Farakka Barrage lateral axis and 180' on their longitudinal axis, (Sinha 1997). Maximum dolphins survive in the to swim on their side in the direction opposite to Ganga mainstein between Allahabad and their surfacing direction. The head sweeps up Farakka. Less than 100 have been estimated in and down in a scanning motion and the deeper Chambal river, a tributary of the Yamuna. A total pectoral fin, or flipper, trails along or slightly of about 2,000 dolphins have been estimated in 28 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(1), APR. 2003 CURRENTSTATUS OF THE GANGES RIVER DOLPHIN IN THE RIVERS KOSI AND SON the Ganga-Brahmaputra river systems in the 1974, Gupta 1986, Ali 1992, Singh and Ahmed Indian territory (Sinha 1999). A few hundreds 1994, Kumar 1996) nothing specific is are present in Bangladesh. A comprehensive mentioned about its status and the reports carry review of the susu's status in the entire Ganga only a general account of the species. Moreover, system including tributaries has recently been the papers record only casual observations on the documented (Sinha et al. 2000). animal in the River Ganga. Based on a systematic In the nineteenth century, dolphins were study, Sinha (1996, 1997 and 1999), Sinha plentiful in the entire distribution range, though et al. (2000) reported the current status and no actual data on populations is available. They distribution of the susu in the Ganga and many were found in the Yamuna as far as Delhi, even of its tributaries. Though the overall estimate of in May when water was very low (Anderson susu abundance in the entire distribution range 1879). In the last couple of decades, no dolphin is not known, the largest sub-population occurs has been sighted in the Yamuna at Delhi. Their in the mainstem of the Ganga and its tributaries current distribution in the Yamuna is mainly in Bihar. Most of the tributaries or parts thereof below the confluence of the Chambal and are yet to be surveyed thoroughly and these Yamuna near Etawah. In most of the small surveys were conducted in an effort to bridge this tributaries, dolphins have become locally extinct gap or are sighted only in the rainy season. Platanista gangetica is legally protected, STUDYAREA being included in Schedule I of the Indian (Fig. 1) Wildlife Protection Act (1 972) and in Appendix I of Convention of International Trade in River Son: The River Son originates from Endangered Species of Wild Fauna and Flora Amarkantak Hills at Sonabhadra, in Madhya (CITES), which prohibits trade in dolphin Pradesh, at an elevation of 600 m. It flows products by signatory countries. northwards through Madhya Pradesh, Uttar Pradesh and Bihar before it discharges into the Past Distribution in Bihar Ganga at Haldi-Chhapra village near Maner, Anderson (1879) has mapped the about 35 km upstream of Patna. In Uttar Pradesh, distribution of dolphins in the entire stretch of it receives the Rihand tributary across which the the Ganga, all its tributaries both large and small, Rihand dam was constructed in 1963.