River dolphins are among the world’s most threatened mammals, and indeed the baiji (Lipotes vexillifer), a species endemic to China's Yangtze River, is likely extinct. Exploitation for products such as meat, oil, and skins has been a lesser feature in the population histories of river dolphins compared to most large mammals. Habitat factors are therefore of particular interest and concern. In this paper we attempt to describe the population-level responses of river dolphins to habitat transformation. We find circumstantial but compelling evidence supporting the view that, at a local scale, river dolphins are opportunists (generalists) capable of adapting to a wide range of habitat conditions while, at a river basin scale, they are more appropriately viewed as vulnerable specialists. The same evidence implies that the distributional responses of river dolphins to basinwide ecological change can be informative about their extinction risk, while their local behaviour patterns may provide important insights about critical ecological attributes. Empirical studies are needed on the ecology of river cetaceans, both to inform conservation efforts on behalf of these threatened animals and to help address broader concerns related to biodiversity conservation and the sustainability of human use in several of the world's largest river systems. 1. Introduction In this paper, we attempt to evaluate the ability of river dolphins to adapt to environmental change. This evaluation is necessarily speculative and largely theoretical. Our goal is to develop ideas and terminology that will facilitate a rigorous debate and stimulate field researchers and resource managers to look at these animals with fresh eyes. Our evaluation is far from academic because the fluvial systems occupied by dolphins have been and continue to be subjected to dramatic environmental changes associated with water development, a general decline in the availability and quality of fresh water, and global climate change. Regarding this last, although global warming will generally result in increased precipitation, the effects will be spatially and temporally uneven, and declines are expected in some areas [1]. Also, sea-level rise is expected to result in the loss of dolphin habitat in the lower reaches of rivers due to salinity encroachment and increased sedimentation [2]. The recent extinction of the Yangtze River dolphin or baiji Lipotes vexillifer [3] adds a sense of urgency for understanding the vulnerability and resilience of freshwater dolphins to environmental change. Although fishery
References
[1]
Intergovernmental Panel on Climate Change (IPCC), “Climate change 2007: the physical basis, summary for policy makers,” World Meteorological Organization and United Nations Environmental Program, 2007, http://www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.html.
[2]
B. D. Smith, G. Braulik, S. Strindberg, R. Mansur, M. A. A. Diyan, and B. Ahmed, “Habitat selection of freshwater-dependent cetaceans and the potential effects of declining freshwater flows and sea-level rise in waterways of the Sundarbans mangrove forest, Bangladesh,” Aquatic Conservation, vol. 19, no. 2, pp. 209–225, 2009.
[3]
S. T. Turvey, R. L. Pitman, B. L. Taylor et al., “First human-caused extinction of a cetacean species?” Biology letters, vol. 3, no. 5, pp. 537–540, 2007.
[4]
X. Zhang, D. Wang, R. Liu et al., “The Yangtze River dolphin or baiji (Lipotes vexillifer): population status and conservation issues in the Yangtze River, China,” Aquatic Conservation, vol. 13, no. 1, pp. 51–64, 2003.
[5]
B. D. Smith, R. K. Sinha, K. Zhou, et al., “Register of water development projects affecting Asian river cetaceans,” in Biology and Conservation of Freshwater Cetaceans in Asia, R. R. Reeves, B. D. Smith, and T. Kasuya, Eds., Occasional papers of the IUCN Species Survival Commission, no. 23, IUCN, Gland, Switzerland, 2000.
[6]
B. D. Smith, K. Zhou, D. Wang, et al., “Lipotes vexillifer,” in: 2008 IUCN Red List of Threatened Species, 2008, http://www.iucnredlist.org/.
[7]
I. Cassens, S. Vicario, V. G. Waddell et al., “Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages,” Proceedings of the National Academy of Sciences of the United States of America, vol. 97, no. 21, pp. 11343–11347, 2000.
[8]
D. W. Rice, Marine Mammals of the World, Systematics and Distribution, Society of Marine Mammalology, Lawrence, Kan, USA, 1998.
[9]
I. Beasley, K. M. Robertson, and P. Arnold, “Description of a new dolphin, the Australian snubfin dolphin Orcaella heinsohni sp. N. (Cetacea, Delphinidae),” Marine Mammal Science, vol. 21, no. 3, pp. 365–400, 2005.
[10]
S. Caballero, F. Trujillo, J. A. Vianna et al., “Taxonomic status of the genus Sotalia: species level ranking for “tucuxi” (Sotalia fluviatilis) and “costero” (Sotalia guianensis) dolphins,” Marine Mammal Science, vol. 23, no. 2, pp. 358–386, 2007.
[11]
H. Hamilton, S. Caballero, A. G. Collins, and R. L. Brownell Jr., “Evolution of river dolphins,” Proceedings of the Royal Society B, vol. 268, no. 1466, pp. 549–556, 2001.
[12]
M. Nikaido, F. Matsuno, H. Hamilton et al., “Retroposon analysis of major cetacean lineages: the monophyly of toothed whales and the paraphyly of river dolphins,” Proceedings of the National Academy of Sciences of the United States of America, vol. 98, no. 13, pp. 7384–7389, 2001.
[13]
A. R. Martin and V. M. F. da Silva, “River dolphins and flooded forest: seasonal habitat use and sexual segregation of botos (Inia geoffrensis) in an extreme cetacean environment,” Journal of Zoology, vol. 263, no. 3, pp. 295–305, 2004.
[14]
G. Pilleri and M. Gihr, “Differences observed on the skull of Platanista indi and gangetica,” Investigations on Cetacea, vol. 4, pp. 44–70, 1971.
[15]
B. D. Smith, “1990 Status and conservation of the Ganges River dolphin Platanista gangetica in the Karnali River, Nepal,” Biological Conservation, vol. 66, no. 3, pp. 159–169, 1993.
[16]
G. T. Braulik, “Status assessment of the Indus River dolphin, Platanista gangetica minor, March-April 2001,” Biological Conservation, vol. 129, no. 4, pp. 579–590, 2006.
[17]
S. K. Choudhary, B. D. Smith, S. Dey, S. Dey, and S. Prakash, “Conservation and biomonitoring in the Vikramshila Gangetic Dolphin Sanctuary, Bihar, India,” Oryx, vol. 40, no. 2, pp. 189–197, 2006.
[18]
R. R. Reeves, S. Leatherwood, and R. S. L. Mohan, A Future for Asian River Dolphins: Report from a Seminar on the Conservation of River Dolphins of the Indian Subcontinent, Whale and Dolphin Conservation Society, London, UK, 1993.
[19]
B. D. Smith and G. T. Braulik, “Platanista gangetica,” in: 2008 IUCN Red List of Threatened Species, 2008, http://www.iucnredlist.org/.
[20]
B. D. Smith and G. T. Braulik, Susu and Bhulan. Encyclopedia of Marine Mammals, Academic Press, San Diego, Calif, USA, 2nd edition, 2009.
[21]
A. R. Martin, V. M. F. da Silva, and D. L. Salmon, “Riverine habitat preferences of botos (Inia geoffrensis) and tucuxis (Sotalia fluviatilis) in the central amazon,” Marine Mammal Science, vol. 20, no. 2, pp. 189–200, 2004.
[22]
R. C. Best and V. M. F. da Silva, “Amazon river dolphin, boto Inia geoffrensis (de Blainville, 1817),” in Handbook of Marine Mammals: River Dolphins and the Larger Toothed Whales, S. H. Ridgeway and R. J. Harrison, Eds., vol. 4, Academic Press, London, UK, 1989.
[23]
R. C. Best and V. M. F. da Silva, “Inia geoffrensis,” Mammalian Species, vol. 426, pp. 1–8, 1993.
[24]
S. Leatherwood, R. R. Reeves, B. Würsig, et al., “Habitat preferences of river dolphins in the Peruvian Amazon,” in Biology and Conservation of Freshwater Cetaceans in Asia, R. R. Reeves, B. D. Smith, and T. Kasuya, Eds., Occasional papers of the IUCN Species Survival Commission, no. 23, IUCN, Gland, Switzerland, 2000.
[25]
A. R. Martin and V. M. F. da Silva, “Number, seasonal movements, and residency characteristics of river dolphins in an Amazonian floodplain lake system,” Canadian Journal of Zoology, vol. 82, no. 8, pp. 1307–1315, 2004.
[26]
R. R. Reeves, T. A. Jefferson, L. Karczmarski, et al., “Inia geoffrensis,” in: 2008 IUCN Red List of Threatened Species, 2008, http://www.iucnredlist.org/.
[27]
P. Chen, P. Liu, R. Liu, et al., “The distribution, ecology, behaviour and protection of dolphins in the middle reach of Changjiang River (Wuhan—Yuayang),” Investigations on Cetacea, vol. 10, pp. 87–103, 1980.
[28]
Y. Hua, Q. Zhao, and G. Zhang, “The habitat and behavior of Lipotes vexillifer,” in Biology and Conservation of the River Dolphins, W. F. Perrin , R. L. Brownell Jr., K. Zhou, et al., Eds., Occasional papers of the IUCN Species Survival Commission, no. 3, IUCN, Gland, Switzerland, 1989.
[29]
K. Zhou and Y. Li, “Status and aspects of the ecology and behaviour of the baiji, Lipotes vexillifer in the lower Yangtze River,” in Biology and Conservation of the River Dolphins, W. F. Perrin, R. L. Brownell Jr., K. Zhou, et al., Eds., Occasional papers of the IUCN Species Survival Commission, no. 3, IUCN, Gland, Switzerland, 1989.
[30]
Cetacean Specialist Group, “Neophocaena phocaenoides ssp. asiaeorientalis,” 2008 IUCN Red List of Threatened Species. 2008 IUCN Red List of Threatened Species, 1996, http://www.iucnredlist.org/.
[31]
T. A. Jefferson and S. K. Hung, “Neophocaena phocaenoides,” Mammalian Species, vol. 746, pp. 1–12, 2004.
[32]
V. M. F. da Silva and R. C. Best, “Tucuxi Sotalia fluviatilis (Gervais, 1853),” in Handbook of Marine Mammals, S. H. Ridgway and R. Harrison, Eds., vol. 5 of The first book of dolphins, Academic Press, London, UK, 1994.
[33]
C. Faustino and V. M. F. da Silva, “Seasonal use of Amazon floodplains by the tucuxi Sotalia fluviatilis (Gervais 1853) in the central Amazon, Brazil,” Latin American Journal of Aquatic Mammals, vol. 2, pp. 95–104, 2006.
[34]
R. R. Reeves, E. A. Crespo, Dans, et al., “Sotalia fluviatilis,” in: 2008 IUCN Red List of Threatened Species, 2008, http://www.iucnredlist.org/.
[35]
B. D. Smith, H. Thant, J. M. Lwin, et al., “Preliminary investigation of cetaceans in the Ayeyarwady River and northern coastal waters of Myanmar,” Asian Marine Biology, vol. 14, pp. 173–184, 1997.
[36]
D. Kreb, X. Budiono, and X. Syachraini, “Status and conservation of Irrawaddy dolphins Orcaella brevirostris in the Mahakam River of Indonesia,” in Status and Conservation of Freshwater Populations of Irrawaddy Dolphins, B. D. Smith, R. G. Shore, and A. Lopez, Eds., WCS working paper, no. 31, Wildlife Conservation Society, Bronx, NY, USA, 2007.
[37]
R. R. Reeves, T. A. Jefferson, L. Karczmarski, et al., “Orcaella brevirostris,” in: 2008 IUCN Red List of Threatened Species, 2008, http://www.iucnredlist.org/.
[38]
B. D. Smith, Irrawaddy Dolphin. Encyclopedia of Marine Mammals, Academic Press, San Diego, Calif, USA, 2nd edition, 2009.
[39]
T. L. McGuire and K. O. Winemiller, “Occurrence patterns, habitat associations, and potential prey of the river dolphin, Inia geoffrensis, in the Cinaruco River, Venezuela,” Biotropica, vol. 30, no. 4, pp. 625–638, 1998.
[40]
B. D. Smith, A. K. M. A. Haque, M. S. Hossain, and A. Khan, “River dolphins in Bangladesh: conservation and the effects of water development,” Environmental Management, vol. 22, no. 3, pp. 323–335, 1998.
[41]
B. D. Smith, M. A. A. Diyan, R. M. Mansur, E. F. Mansur, and B. Ahmed, “Identification and channel characteristics of cetacean “hotspots” in waterways of the Eastern Sundarbans mangrove forest, Bangladesh,” Oryx, vol. 44, no. 2, pp. 241–247, 2010.
[42]
R. C. Connor, “Group living in whales and dolphins,” in Cetacean Societies, Field Studies of Dolphins and Whales, J. Mann, R. C. Connor, P. L. Tyack, et al., Eds., University of Chicago Press, Chicago, Ill, USA, 2000.
[43]
B. D. Smith, M. T. Tun, A. M. Chit, H. Win, and T. Moe, “Catch composition and conservation management of a human-dolphin cooperative cast-net fishery in the Ayeyarwady River, Myanmar,” Biological Conservation, vol. 142, no. 5, pp. 1042–1049, 2009.
[44]
B. D. Smith, G. Braulik, S. Strindberg, B. Ahmed, and R. Mansur, “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, vol. 22, no. 3, pp. 527–547, 2006.
[45]
B. D. Smith, R. G. Shore, and A. Lopez, Eds., Status and Conservation of Freshwater Populations of Irrawaddy Dolphins, WCS working paper, no. 31, Wildlife Conservation Society, Bronx, NY, USA, 2007.
[46]
K. Zhou, G. Pilleri, and Y. Li, “Observation on the Baiji (Lipotes vexillifer) and the finless porpoise (Neophocaena asiaeorientalis) in the Changjiang (Yangtze) River between Nanjing and Taiyangzhou, with remarks on some physiological adaptations of the Baiji to its environment,” Investigations on Cetacea, vol. 10, pp. 109–119, 1980.
[47]
X. Zhao, J. Barlow, B. L. Taylor et al., “Abundance and conservation status of the Yangtze finless porpoise in the Yangtze River, China,” Biological Conservation, vol. 141, no. 12, pp. 3006–3018, 2008.
[48]
G. S. Miller, “The telescoping of the cetacean skull,” Smithsonian Miscellaneous Collections, vol. 76, pp. 1–70, 1923.
[49]
B. C. Choudhury, L. A. K. Singh, R. J. Rao, et al., “Gavialis gangeticus,” 2008 IUCN Red List of Threatened Species, 2007, http://www.iucnredlist.org/.
[50]
J. Anderson, Anatomical and Zoological Researches: Comprising an Account of Zoological Results of the Two Expeditions to Western Yunnan in 1868 and 1875; and a Monograph of the Two Cetacean Genera, Platanista and Orcella, Bernard Quaritch, London, UK, 1879.
[51]
R. K. Sinha, B. D. Smith, G. Sharma, et al., “Status and distribution of the Ganges susu, Platanista gangetica, in the Ganges river system of India and Nepal,” in Biology and Conservation of Freshwater Cetaceans in Asia, R. R. Reeves, B. D. Smith, and T. Kasuya, Eds., Occasional papers of the IUCN Species Survival Commission, no. 23, IUCN, Gland, Switzerland, 2000.
[52]
R. K. Sinha and G. Sharma, “Current status of the Ganges river dolphin in the rivers Kosi and Son,” Journal of the Bombay Natural History Society, vol. 100, no. 1, pp. 27–37, 2003.
[53]
R. R. Reeves and B. D. Smith, “Interrupted migrations and dispersal of river dolphins: some ecological effects of riverine development,” in Proceedings of the Symposium on Animal Migration, Geneva, Switzerland, Bonn, Germany, 1999, CMS technical series publication no. 2.
[54]
B. D. Smith and R. R. Reeves, “Report of the workshop on the effects of water development on river cetaceans in Asia, Rajendrapur, Bangladesh, 26–28 February 1997,” in Biology and Conservation of Freshwater Cetaceans in Asia, R. R. Reeves, B. D. Smith, and T. Kasuya, Eds., Occasional papers of the IUCN Species Survival Commission, no. 23, IUCN, Gland, Switzerland, 2000.
[55]
M. A. Zacharias and J. C. Roff, “Use of focal species in marine conservation and management: a review and critique,” Aquatic Conservation: Marine and Freshwater Ecosystems, vol. 11, no. 1, pp. 59–76, 2001.
[56]
R. R. Reeves and P. J. H. Reijnders, “Conservation and management,” in Marine Mammal Biology, an Evolutionary Approach, R. A. Hoelzel, Ed., Blackwell Science, Oxford, UK, 2002.
[57]
G. K. Meffe and C. R. Carroll, “The species in conservation,” in Principles of Conservation Biology, G. K. Meffe, Ed., Sinauer Associates, Sunderland, Mass, USA, 2nd edition, 1997.
[58]
E. Hoyt, Marine Protected Areas for Whales, Dolphins and Porpoise, a World Handbook for Cetacean Habitat Conservation and Planning, Earthscan, London, UK, 2nd edition, 2011.
