Possible range decline of Ganges River Dolphin Platanista gangetica (Mammalia: Cetartiodactyla: Platanistidae) in Indian Sundarban

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Sangita Mitra
https://orcid.org/0000-0003-2486-3196
Mahua Roy Chowdhury
https://orcid.org/0000-0002-2869-6877

Abstract

Recent survey reports and observations from rivers in southern West Bengal (India) indicate the extirpation of Ganges River Dolphin (GRD) from the Indian Sundarbans. The present study undertaken during 2011–16 reviews the possible factors accountable for the disappearance of this obligatory freshwater cetacean from the major waterways of the Sundarbans, India and conclude that it is due to reasons of anthropogenic and geo-climatic origin.  Sundarbans, the largest contiguous mangrove forest on earth encompassing almost 10,000km2 of India and Bangladesh is located at the head of the Bay of Bengal within 21.533–22.666 0N and 88.083–89.850 0E, of which 62% lies within Bangladesh and 38% in India (Spalding et al. 2010).  The landscape is a network of mudflats and islands at the deltaic mouth of the rivers Ganga, Brahmaputra and Meghna created by accumulated sediments carried by the snow-fed Himalayan rivers and their tributaries along with anastomosing tidal water channels.  Historic reports reveal the occurrence of GRD in the Sundarbans waters of both India and Bangladesh (Anderson 1879).   Current  data, however, confirms the disappearance of Platanista gangetica but there is continued occurrence of Orcaella brevirostris in the Indian part of the estuary.  Analysis of causative factors in light of existing evidence validates the potential extirpation of Platanista from the majority of the Sundarbans in India, except for its persistence in only the westernmost segment in the lower reaches of river Hooghly as confirmed by this study.  The present study also records the habitat preferences and limiting factors affecting GRD distribution, and maps the decline of its range.

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Communications

References

Anderson, J. (1879). Anatomical and Zoological Researches: Comprising an Account of the Zoological Results of the two Expeditions to Western Yunnan in 1868 and 1875 and a Monograph of the two cetacean genera Platanista and Orcaella. Bernard Quaritch, Piccadilly, London.

Bahuguna, N.C. & J.K. Mallick (2010). Handbook of the Mammals of South Asia. Natraj Publishers, Dehra Dun, 541pp

Banerjee, K. (2013). Decadal change in the surface water salinity profile of Indian Sundarbans: A potential indicator of climate change. Journal of Marine Science Research and Development S II: 002; https://doi.org/10.4172/2155-9910.SII-002

Braulik, G.T. & B.D. Smith (2017). Platanista gangetica. The IUCN Red List of Threatened Species 2017. Downloaded on 11 February 2018. https://doi.org/10.2305/IUCN.UK.2017-3.RLTS.T41758A50383612.en

Choudhary, S., B. D. Smith, S. Dey, S. Dey & S. Prakash (2006). Conservation and biomonitoring in the Vikramshila Gangetic Dolphin Sanctuary. Oryx 40(2): 189–197.

Choudhary, S., S. Dey, S. Dey, V. Sagar, T. Naird & N. Kelkar (2012). River dolphin distribution in regulated river systems: implications for dry-season flow regimes in the Gangetic basin. Aquatic Conservation: Marine and Freshwater Ecosystems 22: 11–25.

Choudhuri, A.B. & A. Chaudhury (1994). Mangroves of the Sundarbans, India, IUCN- The World Conservation Union, 1

Choudhury, A. & S. Mitra (2014). Assessing sustainable livelihood strategies for fisherman communities during Hilsa fishing ban period in West Bengal, India. A report by WWF-India supported by IUCN.

Chowdhury, M.R., S. Mitra & S. Sen (2016). On the Behaviour, abundance, habitat use and potential threats of the Gangetic Dolphin Platanista gangetica in southern West Bengal, India. Journal of Threatened Taxa 8(9): 9131–9137; https://doi.org/10.11609/jott.1752.8.9.9131-9137

Jensen, F.H., A. Rocco, R.M. Mansur, B.D. Smith, V.M. Janik, P.T. Madsen & A. Fahlman (editors) (2013). Clicking in shallow Rivers: Short range Echolocation of Irrawaddy & Ganges River Dolphin in Shallow, Acoustically complex habitat. PLoS one 8(4): e59284; https://doi.org/10.1371/journal.pone.0059284

Jones, S. (1982). The present status of the Gangetic Susu Platanista gangetica (Roxburgh) with comments on the Indus Susu P. minor (Owen). FAO Fisheries Series 5: 97–115.

Hamilton, H., S. Caballero, H.G. Collins & R.L. Brownell (2001). Evolution of River dolphins. Proceeding of the Royal Society of London B: Biological Sciences 208(1466): 549–56.

Hussain, M.A., A.K.M.S. Islam, M.A. Islam & B. Bhaskaran (2013). Changes of the seasonal salinity distribution at the Sundarbans coast due to impact of climate change, pp. 637–648. In: Proceedings of 4th International Conference on Water & Flood Management (ICWFM-2013).

Kelkar, N., J. Krishnaswamy, S. Choudhary & D. Samaria (2010). Coexistence of fisheries with river dolphin conservation. Conservation Biology 24: 1130–1140

Kreb, D. & K.D. Rahadi (2004). Living under an aquatic freeway: effects of boats on Irrawaddy Dolphins (Orcaella brevirostris) in a coastal and riverine environment in Indonesia. Aquatic Mammals 30: 363–375.

Lebeck, H.J. (1801). Delphinus gangeticus beschrieben von Heinrich Julius Lebeck zu Trankenbar.— DerGesellschaft naturforschender Freunde zu Berlin Neue Schriften 3: 280-282, Tab. II.

Mandal, A.K. & N.C. Nandi (1989). Fauna of Sundarban Mangrove Ecosystem, West Bengal, India. Fauna of Conservation Area: 3. Zoological Survey of India.

Mansur, E.F., B.D. Smith, R.M. Mowgli & M.A. Abu Diyan (2008). Two Incidents of Fishing Gear Entanglement of Ganges River Dolphins (Platanista gangetica gangetica) in Waterways of the Sundarbans Mangrove Forest, Bangladesh. Aquatic Mammals 34(3): 362–366.

Mitra, A. & K. Banerjee (2011). Trace elements in edible shellfish species from the lower Gangetic delta. Ecotoxicology and Environmental Safety 74: 1512–1517.

Mitra, A., R. Chowdhury, K. Sengupta & K. Banerjee (2010). Impact of salinity on Mangroves of Indian Sundarban. Journal of Coastal Environment 1(1): 71–82.

Mohan, R.S. (1995). Mortality of Ganges River Dolphin, Platanista gangetica, in gillnets of the Ganges and Brahmaputra in India. Tiger Paper 22(1): 11–13.

Mallick, J. (2011). Ecology and Status of the Ganges Dolphin (Platanista gangetica gangetica): India’s National Aquatic Animal, in Southern West Bengal. Animal Diversity, Natural History and Conservation 1: 277–305.

Manna, S., K. Chaudhuri, S. Bhattacharyya & M. Bhattacharyya (2010). Dynamics of Sunderbans estuarine ecosystem: eutrophication induced threat to mangroves. Saline Systems. 6: 8; https://doi.org/10.1186/1746-1448-6-8

Raha, A., S. Das, K. Banerjee & A. Mitra (2012). Climate change impacts on Indian Sunderbans: A time series analysis (1924–2008). Biodiversity Conservation 21: 1289–1307.

Roxburgh, W. (1801). An account of a new species of Delphinus, an inhabitant of the Ganges. Asiatic Research Transactions Society (Calcutta) 7: 170–174, pl.5.

Sinha, R.K. , B. D. Smith, G.Sharma, K.Prasad, B.C.Choudhury, K.Sapkota, R. K. Sharma AND S. K. Behera (2000). Status and distribution of the Ganges susu (Platanista gangetica) in the Ganges river system of India and Nepal. Pages 42–48 inR. R. Reeves, B. D. Smith and T. Kasuya, eds. Biology and conservation of freshwater cetaceans in Asia. Occasional Paper of the IUCN Species Survival Commission No. 23.Gland, Switzerland

Smith, B.D. & R.R. Reeves (2000). Report of the second meeting of the Asian River Dolphin Committee, Rajendrapur, Bangladesh, 22–24 February 1997, pp. 1–14. In: Reeves, R.R., B.D. Smith & T. Kasuya (eds.). Biology and conservation of freshwater cetaceans in Asia (IUCN Occasional Papers Series 23). IUCN, Gland, Switzerland, 152pp.

Smith, B.D., B. Ahmed, M. Edrise & G. Braulik (2001). Status of the Ganges River Dolphin or Shushuk Platanista gangetica in Kaptai Lake and the southern rivers of Bangladesh. Oryx 35(1): 61–72.

Smith, B.D., G. Braulik, S. Strindberg, B. Ahmed & R. Mansur (2006). Abundance of Irrawaddy Dolphins (Orcaella brevirostris) and Ganges River Dolphins (Platanista gangetica gangetica) estimated using concurrent counts made by independent teams in waterways of the Sundarbans mangrove forest in Bangladesh. Marine Mammal Science 22: 527–547.

Smith, B.D., V. Shore & A. Lopez (eds.) (2007). Status and Conservation of Freshwater Populations of Irrawaddy Dolphins. WCS working paper, no. 31, Wildlife Conservation Society, Bronx, NY, USA

Smith, B.D., G. Braulik, S. Strindberg, R. Mansur, M.A.A. Diyan & B. Ahmed (2009). Habitat selection of freshwaterâ€dependent cetaceans and the potential effects of declining freshwater flows and seaâ€level rise in waterways of the Sundarbans mangrove forest, Bangladesh. xxxxxxxx xxxxxxxxxxx 19(2): 209–225.

Smith, B.D., M.A.A. Diyan, R.M. Mansur, E.F. Mansur & B. Ahmed (2010). Identification and channel characteristics of cetacean hotspots in waterways of the eastern Sundarbans mangrove forest, Bangladesh. Oryx 44: 241–247.

Smith, B.D. & R.R. Reeves (2012). River Cetaceans & Habitat Change: Generalist Resilience or Specialist Vulnerability? Journal of Marine Biology 2012: 1–11; https://doi.org/10.1155/2012/718935

Spalding, M., M. Kainuma & L. Collins (2010). World Atlas of Mangroves. Earthscan, London, UK, 319pp.

Trivedi, S., S. Zaman, T.R. Chaudhuri, P. Prmanick, P. Fazli, G. Amin & A. Mitra (2016). Inter annual variation of salinity in Indian Sundarbans. Indian Journal of Geo-Marine Science 45(3): 410–415.