The South Asian river dolphin is divided into two subspecies, one inhabiting the Indus River of Pakistan (Indus River dolphin - Platanista gangetica minor) and the other the Ganges and associated river systems in India and Nepal (Ganges River dolphin - Platanista gangetica gangetica); a subpopulation of P. gangetica gangetica is also found in the Karnaphuli and Sangu Rivers of Bangladesh. Ganges River dolphins reside in the Sundarbans mangrove forest (India and Bangladesh) as well. The most critically endangered subpopulations live upstream in the smaller tributaries of the main rivers, where due to limited habitat space, the effects of human activity are most adversely felt (Sinha et al 2000).
It is estimated that in the past 50 years, there has been a 50% decline in the population of Ganges River dolphins (Wakid & Braulik 2009). The major threats impacting the species are habitat fragmentation, pollution, dam/irrigation canal construction, and accidental entanglement in fishing gear (Wakid 2009). Chief among these is bycatch (Bashir et al 2010). Optimal habitat for the Ganges River dolphin overlaps with heavily-used fishing areas as both animals and humans seek to exploit the same hotspots of bioproductivity, resulting in dolphin entanglement (Bashir et al 2010; Smith & Braulik 2012). Although the Ganges River dolphin is legally protected throughout its range, enforcement is minimal due to a lack of an adequate fisheries and wildlife management agency (Smith & Braulik 2012).
Because of demands for dolphin meat and oil for human consumption, medicinal use, and catfish bait, dolphins are often killed once entangled, and it is not uncommon for fishermen to deliberately set nets in areas where dolphins are likely to encounter them (Sinha 2002; Bashir et al 2010). In 2005, the number of gillnets in the Brahmaputra River was estimated to be five times higher than in 1993 (Wakid 2009). During the 2004-2005 Brahmaputra fishing season, 12 of 14 recorded dolphin deaths were due to gillnet entanglement, although truly accidental deaths and deliberate killings are difficult to distinguish (Wakid 2005; Sinha 2002). It is also believed that the true number of mortality events is higher than the number of recorded deaths (Wakid 2009).
Conservation efforts have been successful in some regions but have failed in others. In Kaziranga National Park (India), mortality rates are low due to a ban on fishing inside park boundaries (Wakid 2009). In the Vikramshila Dolphin Sanctuary, however, enforcement of dolphin protection regulations in negligible (Kelkar et al 2010). It is suggested that future management strategies include population abundance monitoring, further research on bycatch mortality, awareness campaigns and involvement of local people in dolphin conservation attempts, protection of dolphins that migrate through high-use areas in the rain season, and legal consequences for purposeful dolphin killing (Wakid 2009). Although as of 2012 no trials have been carried out, it is also possible that acoustic pingers could serve as net deterrents.
References
Bashir, T, A Khan, P Gautam, & SK Behera. 2010. Abundance and prey availability assessment of Ganges River dolphin (Platanista gangetica gangetica) in a stretch of upper Ganges RIver, India. Aquatic Mammals 36(1): 19-26.
Kelkar, N, J Krishnaswamy, S Choudhary, & D Sutaria. 2010. Coexistence of fisheries with river dolphin conservation. Conservation Biology 24(4): 1130-1140.
Sinha, RK. 2002. An alternative to dolphin oil as a fish attractant in the Ganges River system: conservation of the Ganges River dolphin. Biological Conservation 107: 253-257.
Smith, BD & GT Braulik. 2012. Platanista gangetica. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2 Accessed 1 November 2012. http://www.iucnredlist.org
Wakid, A. 2005. Conservation of Gangetic dolphin in Brahmaputra River, India. Final Technical Report submitted to the BP Conservation Programma and Rufford Small Grant, p. 80.
Wakid, A. 2009. Status and distribution of the endangered Gangetic dolphin (Platanista gangetica gangetica) in the Brahmaputra River within India in 2005. Current Science 97(8): 1143-1151.
Wakid, A & GT Braulik. Protection of endangered Gangetic dolphin in Brahmaputra River, Assam, India. Final reports to IUCN-Sir Peter Scott Fund. 44 pp. PDF available http://cmsdata.iucn.org/downloads/brahmaputra_river_dolphins___ psf_final_report.pdf