MOLECULAR ECOLOGY AND SYSTEMATICS OF SOTALIA DOLPHINS - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 262

ecology studies of Sotalia dolphins, both with immediate application to their
conservation. At the end of the chapter there is a presentation of the prospects for new
discoveries in these fields in the near future.
Keywords : Sotalia , population structure, phylogeography, social structure, molecular
ecology.
I NTRODUCTION
Sotalia dolphins are among the smallest members of the Delphinidae family. These
dolphins occur along the Atlantic coast of Central and South America, as well as in the
Amazon River basin (Figure 1). Marine Sotalia are found from Honduras to the state of Santa
Catarina, in southern Brazil (Simões-Lopes, 1987; da Silva and Best, 1996), in a seemingly
continuous distribution that might be limited from extending southwards by low water surface
temperatures (Borobia et al., 1991). Throughout that range it has many local common names,
such as ―boto-cinza‖ (Brazil), ―tonina‖ (Venezuela and Colombia) and ―lam‖ (Nicaragua).
The distribution of riverine Sotalia comprises most of the Amazon River basin from Brazil as
far as Peru, Ecuador and Colombia (da Silva and Best, 1996). Locally, this dolphin is known
as ―tucuxi‖ (Brazil), ―bufeo-negro‖ or ―bufeo-gris‖ (Colombia and Peru). There are also
records of Sotalia dolphins in the Orinoco River, up to 800 km inland, and some disputed
reports in the Upper Orinoco (Borobia et al., 1991; Boher et al., 1995). Those sightings may
be attributed to marine Sotalia , since it inhabits bays and estuaries and is frequently seen
entering rivers along the South American coast (da Silva and Best, 1996).
Marine and riverine Sotalia are morphologically very alike: both are dark gray in the
dorsum , and light gray, white or pinkish in the ventral area, with a poorly developed lateral
stripe extending from the eye to the pectoral fin. The beak is moderately long and slender, and
the melon small and rounded. The dorsal fin is triangular , pectoral fins are large and the body
is stocky (Jefferson et al., 1993). The main morphological difference between them is size
with a maximum recorded total length for marine Sotalia of 206 cm, in contrast to 152 cm for
freshwater Sotalia (Barros, 1991; da Silva & Best, 1996). There are also meristic and
morphometric differences, but those are modal rather than absolute (Fettuccia, 2006).
Marine and riverine Sotalia are different not only in ecology but in life history traits: they
use different acoustic signals and have distinct reproductive parameters (such as gestation
length and birth seasonality (da Silva & Best, 1996; Rosas & Monteiro-Filho, 2002). Some of
those differences may have arisen as adaptations to the different environments they inhabit.
The infrageneric taxonomy of Sotalia remained uncertain for over a century, and was
solved only recently, when morphological (Monteiro-Filho et al., 2002) and genetic data
(Cunha et al., 2005; Caballero et al., 2007) showed that marine and riverine Sotalia are
different species.