AN INTRODUCTION TO RIVER DOLPHIN SPECIES - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 13

F
Figure 5. Four photos of Inia geoffrensis (A-D) captured at the Tapiche River and at Yanallpa cocha in
the Ucayali River (Peru) by Ruiz-García's team in 2002-2003 and a mosaic of photos (E) of boto
captures at the Napo, Curaray, Napo and Samiria Rivers in 2003 by Ruiz-García´s team (copyright
Diana Alvarez & M. Ruiz-García). (F) An image of an Inia fishing a ―carachama‖ (copyright Tim
Smith).
Similar to the genera Lipotes and Platanista , Inia geoffrensis has unfused cervical
vertebrae that can permit an increase of mobility in the vertebral area compared to other
odontocetes (see Smith & Burrow's chapter 4). It has the largest population of all the river
dolphins and is widely distributed in the Amazon and Orinoco basins (Best & da Silva, 1989)
as well as in the upper Madeira River (da Silva, 1994), all in northern South America. Its
range includes the countries of Bolivia, Brazil, Columbia, Ecuador, Peru, and Venezuela (and
possibly some southern rivers of Guyana) (da Silva, 1994). Restricted to freshwater, the
quality and quantity of the pink river dolphin's habitat is dependent on the season (rain versus
dry) and will shrink considerably during the dry season. They have been observed commonly
in main river channels, lagoons, and confluence areas (see McGuire & Aliaga-Rossel's
chapter 2; Best & da Silva, 1993; Aliaga-Rossel, 2002) mostly alone or in pairs. At times they
have been known to travel hundreds of kilometers (Martin & da Silva, 2004), but they seem
to have a great fidelity and eventually return. Densities of pink river dolphins per linear km
vary and range between 0.21 to 1.55 individuals (Magnusson et al., 1980; Schnapp &
Howroyd, 1992; Aliaga-Rossel, 2002) with their greatest densities expected where their
characin prey are abundant (da Silva, 1983). There appears to be little gene flow among