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Ruiz-Garcia's anecdotal field observations support these claims. For example, during a
population genetics and phylogeography study of river dolphins in the Amazonian river-
system, Ruiz-Garcia intended to capture river dolphins. Even with expert Indian fishermen
and with a 10-meter long wooden boat powered by a 40 horse power engine, only two
Sotalia
specimens were captured (in little lagoons of the Curaray and Samiria rivers at the Peruvian
Amazon) compared to 200
Inia
. In another example, Ruiz-Garcia's team used large nets to
encircle mixed groups of botos and tucuxis (around seven to nine botos and four to six
tucuxis) in the Napo and Curaray rivers. All the botos were caught, but incredibly, in the last
instant, when the nets were perfectly closed, all the tucuxis escaped.
Taxonomy:
of
Sotalia fluviatilis
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Suborder: Odontoceti
Family: Delphinidae
Genus:
Sotalia
Species:
Sotalia fluviatilis
(Gervais & Deville, 1853)
Pontoporia blainvillei
(Franciscana, La Plata Dolphin)
Pontoporia blainvillei
is a small dolphin species that has a gray, brown, to dark-yellowish
dorsum that is comparatively darker than its flanks and ventral region (Figure 4). Key
characteristics for this species include the fluke width to body length ratio (greater than 1:4)
(Brownell, 1989) and an elongated, slender rostrum which is the longest of any dolphin
relative to its body size. Both its broad flippers and dorsal fin have rounded tips and its dorsal
fin is triangular and tall. They have small eyes, rounded head and a mouth that contains 250
small, sharp teeth (Bastida et al., 2007). And, similar to other river dolphin species it has
unfused cervical vertebrae. It has a short life span (usually less than 12 years) (Pinedo, 1991)
compared to other cetaceans and reaches sexual maturity quickly in two to three years
(Kasuya & Brownell, 1979) and has birth intervals of approximately 1.5 years. Sexual
dimorphism exists with female franciscanas slightly larger than males (1.53 versus 1.35
meters). Two geographical body forms exist for this species with smaller forms in the
northern range and larger forms in the coastal waters (Pinedo 1995). There are no-overall
population estimates at this time for this dolphin species, but limited surveys show that
densities vary from 0.056 to 0.657 ind/km2. Their distribution range consists of the southern
Brazil, Uruguay and Argentina coasts, estuaries (Santos et al. 2009) as well as the La Plata
River and Babitonga Bay Estuaries in Uruguay (Cremer & Simoes-Lopes, 2005).
Franciscanas are not continuously distributed across their range and studies indicate that their
populations are genetically distinct from each other (Lazáro et al., 2004). They prefer turbid
waters shallower than 30-35 meters deep (Pinedo et al., 1989; Danilewicz et al., 2009) and are
considered an opportunistic predator that feed on small fish cephalopods and crustaceans
(Danilewicz et al., 2002). The major threat for this dolphin species is mortality due to fishing,
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