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Dolphins, Whales and Porpoises: 2002-2010 Conservation - IUCN

Dolphins, Whales and Porpoises: 2002-2010 Conservation - IUCN

Figure 28. An Irrawaddy

Figure 28. An Irrawaddy dolphin near Hang Sadam, a small fishing village on an island in the Mekong River along the border between Lao P.D.R. and Cambodia, March or April 1994. Freshwater populations of this species are gravely threatened by incidental mortality in fishing gear and by dams and other forms of water development. Photo: Pam Stacey. Sea. Particular emphasis should be placed on identifying areas of cetacean abundance (“hotspots”) for special conservation attention. It is also important to locate areas of intensive fishing during the surveys. Biopsies should be collected to investigate genetic population structure, particularly for spinner dolphins. Information from the surveys should facilitate development of a conservation plan to guide government policies and manage economic development activities. 10. Investigate the status of coastal small cetaceans in Thailand A diverse cetacean fauna has been recorded for Thailand (Chantrapornsyl et al. 1998; Andersen and Kinze 1999). However, accidental killing in gillnets, deliberate removals for dolphinaria, reduced prey abundance caused by overfishing, and the destruction of mangrove habitat vital for fish reproduction have drastically reduced cetacean numbers in some areas (IWC 1994a, p.110). The Irrawaddy dolphin, finless porpoise, and Indo-Pacific hump-backed dolphin are probably the most severely affected species because of their near-shore distribution and susceptibility to entanglement. Recent surveys revealed that Irrawaddy dolphins have almost entirely disappeared from Songkhla Lake, a large lagoon system connected to the Gulf of Thailand that may have harbored a substantial resident dolphin population in the past (Beasley et al. 2002b). A dwarf form of the spinner dolphin has been described from specimens caught by shrimp trawlers operating in the Gulf of Thailand. If these animals belong to a discrete breeding population, the impact of the shrimp fishery alone could put that population in jeopardy (Perrin et al. 1989). Much information on cetaceans in Thailand has been obtained through a stranding network centered at the Phuket Marine Biological Center (Chantrapornsyl 1996; Chantrapornsyl et al. 1996, 1998). Interview surveys have also provided information on cetacean distribution (Andersen and Kinze 1999). There is a need for at-sea surveys to assess cetacean abundance and distribution in the Gulf of Thailand and Andaman 11. Assess populations and habitat of Ganges dolphins (susus) and Irrawaddy dolphins in the Sundarbans of India and Bangladesh In recent years, much has been learned about the status of Ganges dolphins in India and Bangladesh (e.g., Mohan et al. 1997; Sinha 1997; Smith et al. 1998, 2001; Sinha et al. 2000) and freshwater populations of Irrawaddy dolphins in parts of Southeast Asia and Indonesia (e.g., Baird and Mounsouphom 1997; Smith et al. 1997a, 1997b; Smith and Hobbs 2002; Beasley et al. 2002b; Kreb 1999, 2002). However, little research has been conducted in the one area where the ranges of the two species are known to overlap extensively: the Sundarbans of India and Bangladesh. This is despite the fact that threats to cetaceans in the Sundarbans are increasing: accidental entanglement in gillnets, destruction of fish-spawning habitat through mangrove deforestation, toxic contamination from upstream “mega-cities” (Calcutta and Dhaka), non-selective catch of fish fingerlings and crustacean larvae in “mosquito nets” (Figure 29), and ship traffic. The situation is complicated by saline encroachment during the dry season, particularly on the Bangladesh Figure 29. The ecological effects of intensive fishing can be truly devastating, not only to biodiversity but also to the long-term food security of people. In the Sundarbans Delta of Bangladesh, the widespread use of very fine-mesh nets (locally called rocket jahl) for catching shrimp fry to stock aquaculture ponds results in a massive bycatch of fish fingerlings. Although difficult to document and quantify, the implications for dolphin populations that inhabit such fresh- and brackish-water environments (e.g., Ganges dolphins, Irrawaddy dolphins, and Indo-Pacific hump-backed dolphins) are a serious concern. Photo: Brian D. Smith. 60

side of the Sundarbans, as a result of freshwater diversion and sub-surface extraction upstream in the Ganges Basin. Large portions of the delta are within UNESCO World Heritage sites. This project should entail a training course for local researchers, followed by a field survey of waterways within the delta. The survey should include the collection of fishery data and the measurement of salinity and other physical parameters, as well as standard observations of dolphins and other fauna. One objective is to identify factors that limit the downstream range of the Ganges dolphin and the upstream range of the Irrawaddy dolphin in order to evaluate the effects on both species of further salinity flux in the Sundarbans (e.g., caused by upstream damming and diversion of fresh river waters). The feasibility of using nature tourism to assist in long-term monitoring of dolphin populations should be evaluated. As with several projects included in this Action Plan, collaboration should be sought with other biodiversity initiatives in the region, including the work of other SSC specialist groups (e.g., crocodilian, otter, freshwater turtle). 12. Investigate the use of dolphin oil as a fish attractant in the Brahmaputra River and conduct one or more experiments to test potential substitutes Dolphin meat, intestines, and oil are used as fish attractant in the Ganges and Brahmaputra rivers of India and Bangladesh. In the Brahmaputra River, fishermen trail bound pieces of dolphin body parts alongside small boats while sprinkling the water with a mixture of oil and minced dolphin flesh. Small unbaited hooks are used to catch the fish as they come to the surface within the oil slick (Smith et al. 1998). Judging by the number of dolphin carcasses needed to supply fisheries that use dolphin oil, the number of animals killed is almost certainly unsustainable (Mohan et al. 1997; Bairagi 1999). Surveys of a 178km segment of the Brahmaputra River downstream of Guhuwati (Assam, India) in April 1999 found that dolphins had an extremely clumped distribution, with about three-quarters of the observed animals located in four counter-current areas (R.S.L. Mohan and B.D. Smith, unpublished data). Most of the fishing activity, especially with gillnets, was observed in these same areas. The overlap between prime fishing grounds and dolphin concentrations means that the dolphins are at risk of being taken accidentally, and perhaps deliberately. The market value of dolphin products creates an incentive for directed hunting and for fishermen to kill dolphins found alive in nets. This project should document details of the dolphin oil fishery, including the number of people and boats involved, economic value of the fish, income levels of the fishermen, market value of dolphin carcasses, and how these are procured. A rigorous experiment (or field trial) should be conducted to test the effectiveness of alternative attractants such as sardines or scraps from locally caught fish. The results of trials in the Ganges have been encouraging (Sinha 2002). If other oils are found to be as effective as dolphin oil, a practical plan must be implemented to make these available to local fishermen. 13. Assess the distribution, abundance, and habitat of Ganges river dolphins and monitor ongoing threats – India and Bangladesh Local and foreign scientists have conducted numerous surveys of dolphins in the Ganges-Brahmaputra-Megna and Karnaphuli-Sangu river systems since this project was initially proposed (Perrin 1988; Smith et al. 1994, 1998, 2001; Mohan et al. 1997, 1998; Sinha 1997, 2000; Ahmed 2000; Sinha et al. 2000)(Figure 30). Additional effort is nevertheless required to assess populations, habitat, and threats in rivers or portions of rivers that have not yet been surveyed. The status of river dolphins is unknown in the entire Sundarbans (Project 11, above) and in the Yamuna River between Delhi and the confluence of the Chambal River. Large-scale water abstraction for agricultural, industrial, and urban use has severely reduced dry-season flow in this latter segment. Information is also lacking on the status of dolphins in the entire Damodar river system, the Teesta tributary of the Brahmaputra, and the Burhi Gandak, Gomti, Mahananda and Ghaghara (downstream of the Girijapur Barrage) tributaries of the Ganges. It is also important to monitor the status of dolphins in areas that have been Figure 30. A Ganges River dolphin, locally called shushuk in Bangladesh, surfaces in the Karnaphuli River. The small population inhabiting the Karnaphuli-Sangu river complex in southern Bangladesh (a count of 125 individuals in a 1999 survey provides a lower bound of population size) is relatively isolated from those in the much larger Ganges, Brahmaputra, and Meghna river systems. Photo: Brian D. Smith. 61

Dolphins, Whales and Porpoises: 2002-2010 Conservation - IUCN
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