Sotalia fluviatilis
gray dolphin
(Also: tucuxi)

Sotalia fluviatilis, commonly known as the tucuxi or river dolphin, includes two subspecies, the riverine S. f. fluviatilis, and the marine S. f. guianensis. The riverine tucuxi is found in the main tributaries of the Amazon Basin in northern Brazil, Peru, Colombia, and Ecuador. The marine tucuxi is found along the Atlantic coastlines of South and Central America. (da Silva and Best 1996, Nowak 1999)

S. fluviatilis can be found in fresh or salt water. Marine S. fluviatilis are found in shallow and protected estuarine waters, bays, and mouth of large rivers. Riverine S. f. fluviatilis are found in the main channels of tributaries as well as in large lakes, but they do not enter flooded forest and avoid rapids. (da Silva and Best 1996, Nowak 1999)

Sotalia fluviatilis is a small dolphin with a mean body length of 1.7 m for the marine tucuxi and 1.4 m for the riverine tucuxi. The dorsal fin is triangular in shape, curved to the back, and is approximately 11-13 cm in height. The flippers are slightly broader in comparison to other dolphins. The eyes are about 18 mm in diameter. The iris is brown with a longitudinal oval pupil. In general, the tucuxi is dark gray on its dorsal side and pale pink on its ventral side with a distinct line separating these two regions. An area of pale gray starts behind the pectoral fin and another gray area starts from the mid-body and runs to the anus.

In the marine S. f. guianensis, the upper colorings range from pale bluish gray to brown or black. The color of the back extends to a circle around the eye, onto the pectoral fin, and to the sides of the tail. Some populations have yellow-orange sides with a bright patch on the sides of the dorsal fin.

In S. f. fluviatilis, the upper parts are bluish or pearl gray. Furthermore, the tip of the beak and tip of the dorsal fin are occassionally white. S. fluviatilis is often confused with a smaller version of bottlenose dolphin. However, its internal structure provides distinguishing features -- undivided nasal sacs and partially unfused neck vertebrae. Sotalia has 26-35 teeth on each side of the jaw. (da Silva 1996, Nowak 1999, Gewalt 1990)

Sotalia is found to be most active in early morning or late afternoon. It is a slow swimmer and rarely jumps from the water. However, in the wild populations this species displays acrobatics and behaviors such as vertical and lateral jumps, somersaults, surfing in the waves of the boats, and rolling on the surface of the water. Captive tucuxi do not display aerial stunts voluntarily.

The two types of tucuxi have similar social groupings with 1-30 individuals. Groups often swim in perfect synchrony.

Sotalia fluviatilis produces echolocation at 8-15 kHz, 30 kHz, and 95 kHz. The rates of the clicks are 10-70 per second when animal is moving. The short pulses and high rates of repetition allow distinction of objects at distances less then 15 cm. Whistling has also been reported in the wild riverine tucuxi, and a higher frequency whistle has been reported when the animals are agitated in captivity.

Aggressive behavior occurs amongst males during breeding season. (Nowak 1999,da Silva and Best 1996).

The diet contains mostly fish and shrimp. The following seafoods have also been found in the stomach of the tucuxi: pelagic lupeids, demersal scianids, neritic cephalopods, and anchovies. (Nowak 1999, da Silva and Best 1996)

S. fluviatilis has been intentionally captured to be used as bait for sharks in Brazil. (da Silva and Best 1996)

The greatest danger to both subspecies is incidental capture in the fishing nets belonging to large commerical fisheries. Other concerns are water pollution and hydroelectric dams. The species has been listed under Appendix I since 1982. Sotalia is considered "insufficiently known" by IUCN. In Brazil, it is protected under the Federal Fisheries Law. An organization in Brazil, the IWC/Brasil's Biologist, started the Sotalia Project in 1991 to study the behavior and habitat needs of S. fluviatilis. Furthermore, the group aims to gain more knowledge on how humans impact the tucuxi's residence in Brazil. There have already been hundreds of photo-identifications of the dolphins. (Nowak 1999,da Silva and Best 1996, Flores 1996)

Many South Americans regard the tucuxi as a sacred animal, consider it a good companion and protector, and believe that it will bring the bodies of drowned persons back to shore. (Nowak 1999)