(Gervais, 1853) - Tucuxi
Distinctive Characteristics
This small dolphin resembles the bottlenose dolphin in body shape; it is rather chunky. The snout is longer and narrower, the flippers are broader, and the dorsal fin is shorter and more triangular than in the bottlenose dolphin.
Dorsally, dolphins of the genus Sotalia are dark bluish or brownish grey, fading to light grey or white on the belly. Much of the light ventral area may be pinkish. There is a broad, somewhat indistinct stripe from the eye to the flipper and often light zones on the sides above the flippers.
The mouth contains 26 to 35 teeth in each row.
There are 2 forms of Sotalia, one found in rivers and lakes, and another in marine waters. Most of the information available on the species' biology comes from studies of the riverine form, and may not apply to those along the coast.
Can be confused with
In the rivers, it is often difficult to distinguish Tucuxi from Boto at a distance. Up close, however, differences in dorsal-fin shape, head shape, and behaviour are the best clues to distinguishing them. Bottlenose dolphins could be mistaken for Sotalia along the coast, but they are much larger, with taller dorsal fins. Franciscana might also be difficult to distinguish from Sotalia in coastal waters. The franciscana has a larger body, much longer snout, and squarish (rather than pointed) flippers.
Size
Adult dolphins of the genus Sotalia are up to 2.1 m (coastal) and 1.6 m (riverine) in length. They reach weights of up to at least 40 kg. Size at birth is between 0.7 and 0.8 m.
Geographical Distribution
This dolphin is found mostly nearshore and in estuaries along the Atlantic coast, from Panama (perhaps Honduras) to southern Brazil. There are separate marine and freshwater populations. The latter are found in the Amazon and Orinoco drainage basins, as far inland as southern Peru, eastern Ecuador, and southeastern Colombia.
Biology and Behaviour
Dolphins of the genus Sotalia live mostly in groups of 4 or fewer, although they are found in groups of up to 20 (in freshwater) or 50 (in marine waters). They are generally shy and difficult to approach. During the flood season, riverine animals may move into smaller tributaries, but apparently do not move into the inundated forest to feed (as Boto do), staying mostly in the main river channels.
In Brazil, calving in the riverine form apparently occurs primarily during the low water period, October to November. Little else is known of the species' reproduction.
A wide variety of fish, mostly small schooling species, are eaten by riverine tucuxi. Those along the coast consume pelagic and demersal fish and cephalopods.
Exploitation
Coastal and riverine Sotalia are taken in gillnets, seines, and shrimp traps. In the Amazon, there may be some direct captures, and there is at least one record of harpooning a coastal animal. The coastal form is sometimes used for human consumption and as shark bait. Damming of the Amazon River potentially can cause isolation of segments of the population and reduce food supplies. Destruction and degradation of mangroves and exposure to polluted waters are other potential problems for this species.
IUCN Status
Insufficiently known.