POPULATION STATUS AND CONSERVATION OF THE GANGES RIVER DOLPHIN (PLATANISTA GANGETICA GANGETICA) IN THE INDIAN SUBCONTINENT - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 422

onshore to feed on vegetation (as the modern Hippopotamus does) or foraged on invertebrates
or aquatic vegetation. Raoellids are the sister group to cetaceans, and this implies that aquatic
habitats originated before the Order Cetacea. The great evolutionary change that occurred at
the origin of cetaceans is thus not the adoption of an aquatic lifestyle but dietary change was
the event that defined cetacean origins. Cetaceans originated from an Indohyus -like ancestor
and switched to a diet of aquatic prey. Significant changes in the morphology of the teeth, the
oral skeleton and the sense organs made cetaceans different from their ancestors and unique
among mammals (Thewissen et al., 2007).
The River Dolphins
The four genera of toothed cetaceans, i.e., the baiji, Lipotes vexillifer ; the susu, Platanista
gangetica , the boto, Inia geoffrensis ; and the franciscana, Pontoporia blainvillei ; comprise the
peculiar and poorly known ‗river dolphins'. The modern river dolphins occur only in two
continents: Asia and South America. The baijii Lipotes vexillifer (the Yangtze River
Dolphin), is endemic to China but was declared functionally/effectively extinct in December
2006, an event which the news media broadcasted worldwide. Either with a glimmer of hope,
or more likely, not-updated, the IUCN Red List of Threatened Species lists the Baiji, Yangtze
River dolphin ( Lipotes vexillifer ) as ‗critically endangered (possibly extinct)' (Hopkin, 2007).
The two populations of Platanista gangetica have been isolated for a considerable time with
P. gangetica minor being confined to the Indus drainage in Pakistan. However, a couple of
this species were sighted in the Sutlej River, a tributary of the Indus, in Punjab state in India
in 2008. P. g. gangetica occurs in the Ganges, Brahmaputra, Meghna, Karnaphuli, and Sangu
drainage systems of India, Bangladesh and Nepal. The boto, Inia geoffrensis has an
extraordinarily wide distribution. It can be found along the entire Amazon River and its
tributaries, small rivers and lakes, throughout the Orinoco river basin. It occurs in six
countries of South America: Bolivia, Brazil, Colombia, Ecuador, Peru, and Venezuela. The
franciscana, Pontoporia blainvillei is the only one of the four river dolphin species living in
the marine environment. It lives in coastal marine waters of eastern South America between
Argentina and Uruguay.
Freshwater dolphins in Asia are among the world's most endangered mammals and there
is an urgent need to establish conservation priorities based on scientifically credible
abundance estimates (Perrin & Brownell, 1989; Smith & Reeves, 2000a; IWC, 2001; Smith
& Jefferson, 2002). The complex geomorphology of freshwater and estuarine systems tends
to concentrate the distribution of cetaceans in counter-current associated with confluences,
meanders and mid-channel islands (Hua et al., 1989; Smith, 1993; Smith et al., 1997, 1998).
The murky river water makes it totally invisible under water. Many times surfacing is very
quiescent and whenever they come up it is usually for only a fraction of a second. All these
limitations make the credible abundance estimates of these dolphins a great challenge.
Extensive population fragmentation has resulted from the widespread construction of barrages
(Smith & Reeves, 2000a; Smith et al., 2000).