The principal threat to the Irrawaddy dolphin throughout much of its range is accidental entanglement in gillnets (Smith et al 2007). Freshwater populations of the species are at the most risk, particularly those inhabiting the Mekong River (Cambodia, Lao PDR, Vietnam), the Mahakam River (Indonesia), the Ayeyarwaddy River (Myanmar), and lakes Chilika (India) and Songkhla (Thailand). These areas are considered high-use habitat due to their biological productivity, and there is frequently overlap between dolphin populations and gillnet fisheries (Smith et al 2006). The Malampaya Sound subpopulation (Philippines) is listed as Critically Endangered by the IUCN, as are the Ayeyarwaddy, Mahakam, Mekong, and Songkhla subpopulations.
Gillnet entanglement caused 87% of 15 deaths from 2001-2005 in the Mekong River, and 66% of 44 deaths in the Mahakam River from 1995-2005 (Beasley et al 2007; Kreb et al 2007). Ayeyarwaddy and Mahakam dolphins are also threatened by illegal electrical fishing (Smith et al 2007). In Bangladesh, drift gillnets for elasmobranch species cause additional deaths (Smith et al 2005), and in Malampaya Sound, entanglement in bottom-set gillnets for crab result in an annual mortality rate of marine Irrawaddy dolphins between 2.6 and 4.4% (Smith et al 2004). Further assessments of population size and structure are needed in almost all regions of the species' range in order to more fully analyze the effects of entanglements (Smith & Hobbs 2002).
In 2007 an action plan for the conservation of freshwater Irrawaddy dolphins, detailing mitigation measures designed to reduce bycatch of the species, was published by the Wildlife Conservation Society. Methods include (1) the establishment of multiple-use protected areas and areas of no or controlled gillnetting, (2) the training of fishermen in how to release entangled dolphins, (3) enforced net checking, (4) the use of alternative fishing methods and or introduction of acoustic pingers and reflective nets, (5) finding other employ for fishermen, (6) increasing the cost of gillnetting permits to make this type of fishing prohibitively expensive while at the same time lowering costs for other fishing permits, and (7) creating a program through which fishermen are remunerated for gear damaged by dolphins (Smith et al 2007).
References
Beasley, I, S Phay, M Gilbert, C Phothitay, S Yim, KS Lor, & S Kim. 2007. Review of the stations and conservation of Irrawaddy dolphins Orcaella brevirostris in the Mekong River of Cambodia, Lao PDR and Vietnam. In BD Smith, RG Shore, & A Lopez (eds), Status and conservation of freshwater populations of Irrawaddy dolphins. pp. 67-82. WCS Working Papers No. 31.
Kreb, D, Budiono & Syachraini. Review of the status and conservation of Irrawaddy dolphins Orcaella brevirostris in the Mahakam River of East Kalimantani, Indonesia. In BD Smith, RG Shore, & A Lopez (eds), Status and conservation of freshwater populations of Irrawaddy dolphins, pp. 53-66. WCS Working Papers No. 31.
Smith, BD & L Hobbs. 2002. Status of Irrawaddy dolphins Orcaella brevirostris in the upper reaches of the Ayeyarwaddy River, Myanmar. Raffles Bulletin of Zoology Supplement No. 10: 67-73.
Smith, BD, I Beaseley, M Buccat, V Calderon, R Evina, JL de Valle, A Cadigal, E Tura, & Z Visitacion. 2004. Status, ecology, and conservation of Irrawaddy dolphins (Orcaella brevirostris) in Malampaya Sound, Palawan, Philippines. J. Cetacean Res. Manage. 6(1): 41-52.
Smith, BD, B Ahmed, R Mansur, T Tint, & TT Mya. 2005. New information on the status of finless porpoises Neophocaena phocaenoides and Irrawaddy dolphins Orcaella brevirostris in Bangladesh and Myanmar. International Whaling Commission, Scientific Committee Document Sc/57/SM4.
Smith, BD, 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(3): 527-547.
Smith, BD, RG Shore, & A Lopez. 2007. Status and conservation of freshwater populations of Irrawaddy dolphins. WCS Working Papers No. 31. PDF available http://www.iucn-csg.org/wp-content/uploads/2010/03/wcswp31.pdf. Accessed 24 Oct. 2012.