Tucuxi dolphin  (Sotalia fluviatilis)

The tucuxi dolphin (pronounced ‘too-koo-shee') quite closely resembles the bottlenose dolphin, but smaller. It is blue to light grey on the back, and fades to white or whitish-pink on the belly. There is a dark bar between the mouth and the flipper. The beak is slender and long, and the dorsal fin is triangular and slightly hooked at the tip (2). Both the beak and the dorsal fin may be tipped with white (5). Some marine populations have yellow-orange sides with a bright patch on the dorsal fin (5).

Occurring in the river systems of the Amazon and the Orinoco, as well as along the coasts from Brazil to Nicaragua, the tucuxi dolphin is split into two subspecies. The freshwater subspecies, Sotalia fluviatilis fluviatilis, inhabits only fresh water and is found as much as 250 kilometres up the Orinoco River system and as much as 2,500 km up the Amazon River system. The marine subspecies, Sotalia fluviatilis guianensis, is found in the coastal estuaries and bays of the east coast of South America as far south as the Brazilian city of Florianópolis (2).

The freshwater subspecies inhabits rivers and lakes, but is not found in flooded forests and avoids rapids, whereas the marine subspecies inhabits shallow, protected estuaries and bays (2).

Little is known of the reproductive habits of the tucuxi dolphin. The freshwater subspecies calves during the low water period of October and November (2), after an 11 to 12 month gestation. It is thought to be polyandrous (where each female has more than one male partner), and aggression between males is seen during courtship (5).

The seasonal fluctuation in river water levels has a great influence on the freshwater subspecies. It enters lakes during high water but leaves as the waters begin to fall to avoid being trapped (2). A shy dolphin, the tucuxi tends to be most active during the early morning and late afternoon, but is usually a slow swimmer that jumps infrequently (5). It dives for around 30 seconds (4), and uses echolocation to communicate as well as to catch fish and shrimp (5). Group size varies, but can be up to 20 in freshwater or 50 in the marine subspecies (3).

The tucuxi dolphin is regularly caught accidentally in gillnets of large fishing trawlers, and is the most common cetacean in the by-catch of coastal fisheries in the south Caribbean Sea. Intentional hunting appears to be rare, but does take place for meat to eat, for blubber to be used as shark bait, and for the genital organs and eyes which are sold as love amulets (1). A major potential threat is a proposal for the construction of hydroelectric dams, which would cause population fragmentation and increased inbreeding, as well as the extinction of the migratory fish that constitute the diet of the freshwater tucuxi dolphin (2). Pollution from heavy metals, banned pesticides and noise are also concerns, as is habitat loss (1).

The superstition of fishermen, who believe the tucuxi dolphin to be a sacred animal that brings the bodies of drowned people back to the shore, has ensured that it has rarely been targeted as a food item (6). In 1994, the International Whaling Commission's (IWC) Scientific Committee urged member states to reduce by-catch and monitor populations (1). The IWC had previously started the Sotalia Project with the organisation ‘Brasil's Biologists', which sets out to study the behaviour and habitat needs of the tucuxi dolphin, and has managed to build a significant collection of photo identifications (6).

For further information on the tucuxi see:

• Convention on Migratory Species:
  http://www.cms.int/reports/small_cetaceans/data/S_fluviatilis/s_fluviatilis.htm

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