AN INTRODUCTION TO RIVER DOLPHIN SPECIES - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 7

forms classified as different species, a taxonomic decision that was based on morphological
and molecular data. Cunha et al. (this topic; chapter 14) suggests that this split occurred
during the Pliocene, 2.5-5 million years ago (also see Caballero et al.'s phylogeographical
analysis in chapter 15). The riverine form has a dark gray dorsum and a white or pinkish
ventral area. It also possesses a moderately long slender beak, small rounded melon, large
pectoral fins, stocky body and a triangular dorsal fin (Jefferson et al., 1993)
Figure 3. A Sotalia fluviatilis at the mouth of the Napo River in the Peruvian Amazon (copyright Pablo
Escobar-Armel).
Sotalia fluviatilis is distributed throughout most of the Amazon River and its tributaries
(Da Silva & Best, 1994) and have also been sighted in the Orinoco River (Borobia et al.,
1991; Boher et al., 1995). There distribution extends from Brazil to Peru, Ecuador and
Columbia (da Silva & Best, 1996). They demonstrate strong site fidelity but there appears to
be high levels of gene flow among their Amazonian population units compared to those of S.
guianensis (Caballero, 2006). S. fluviatilis' main threat is entanglement in gillnets (Trujillo et
al., 2000) and is the most accidently captured dolphin in some Amazonian rivers (Barros &
Teixeira, 1994; Siciliano, 1994). Other factors including habitat destruction, oil and pesticide
pollution (Monteiro-Neto et al., 2003; Yogue et al., 2003), heavy metal contamination (Best
& Silva, 1989), dam construction (da Silva & Best, 1996) and direct killing for specific
organs (da Silva & Best, 1996; Siciliano, 1994) in combination with the problem of bycatch
and growing coastal development have led some researchers (Barros & Teixeira, 1994) and
the country of Ecuador (Tirira, 2001) to consider it endangered. Currently, IUCN lists Sotalia
fluviatilis in the category of ―data deficient‖. This species lives in the sympatric Amazonian
area together with Inia , but does not have a mythological Indian tradition as developed as that
of Inia and their tissues are not frequently sought after for love charms. Additionally, Sotalia
fluviatilis is a much faster and more efficient swimmer than Inia , and also possesses amazing
and superior agility. Therefore, fishermen find them comparatively, difficult to hunt and they
are not used as bait to attract small catfishes, like the ―mota‖ or ―mapurito‖ ( Calophysus
macropterus ) as in the Orinoco and in the Amazon rivers (Colombia and Brazil, mainly).