The Raffles Bulletin of Zoology (2002)


Irrawaddy dolphins Orcaella brevirostris and finless porpoises Neophocaena phocaenoides are referred to as facultative freshwater cetaceans because they occupy both fresh- and nearshore marine waters. In Asia, the especially rapid growth of human populations and their consequent resource demands have had profound impacts on these environments and the biodiversity that they sustain. Facultative freshwater cetaceans and other aquatic species inhabiting these waters are particularly threatened by intensive fishing with non-selective gear, vessel traffic, environmental degradation from water development (most notably dams), land reclamation, and the input of large quantities of toxic contaminants, especially those with bioaccumulative properties. Populations of finless porpoises in the Yangtze River and Inland Sea of Japan, and Irrawaddy dolphins in the Mahakam River, Malampaya Sound and Songkhla Lake, and probably the Mekong River and Chilkha Lake, are at risk of extirpation in the immediate future. The general absence of knowledge regarding the abundance and population structure (and even species occurrence in some areas) has prevented a comprehensive assessment of both species. To provide conservation guidance we liberally adapt a set of conservation principles developed for marine mammals (see Meffe et aI., 1999) to the specific survival requirements (in the holistic sense) of facultative freshwater cetaceans in Asia and give practical advice for their implementation.