(de Blainville, 1817) - Boto
The boto, or Amazon River dolphin, is probably the best-known of the river dolphins. These animals are moderately robust, and have long beaks and steep bulbous foreheads, which are capable of changing shape. There is no true dorsal fin, but only a dorsal ridge that is low and wide-based. The flippers are large and triangular, with blunt tips, and the flukes have a concave trailing edge that is often ragged. The eyes are small, but not as small as those of the Ganges River dolphin or Indus River dolphin.
Botos are grey to pink above and lighter below; some individuals are totally pink. In general, young animals are mostly uniform dark grey; they become progressively more pinkish with age. The extreme colour is so unique that the boto is often called the pink dolphin.
The mouth is lined with 23 to 35 stout teeth in each row. This is the only species of cetacean with differentiated teeth; those at the front of the jaw are typically conical, but those near the rear are flanged on the inside.
Can be confused with
The only other dolphin that inhabits the range of the boto is Sotalia. This latter species is much smaller, has a taller dorsal fin, and more spritely dolphin-like movements.
Adult size ranges to 2.3 m (females) or 2.8 m (males). Males can reach maximum weights of 160 kg. At birth, boto are about 80 cm long.
Boto are endemic to the Amazon and Orinoco drainage basins of South America. Their distribution extends to the upper reaches (impassible falls or rapids) of these rivers and their tributaries in Guyana, Colombia, Ecuador, Peru, and Bolivia, as well as the lower reaches in Brazil and Venezuela. They are found widely not only in the main river channels, but also in smaller tributaries, lakes, and (seasonally) the flooded forest.
Biology and Behaviour
Groups of up to 12 to 15 have been observed, but most boto are seen singly or in small groups. They generally move slowly, and surface at a shallow angle, showing the top of the head and the dorsal ridge. Their responses to humans can range from shyness to curiosity.
In Brazil, births apparently occur in May to July, the season of peak flooding.
These animals feed on a large variety of fishes, generally near the bottom. Some of their prey have hard outer shells, and dolphins have been observed breaking up their larger prey before swallowing. They sometimes feed in a coordinated manner, occasionally with Sotalia.
Boto are threatened by various activities, among them are incidental catches in fisheries, damming of rivers associated with hydroelectric development, deforestation, and pollution from mercury mining operations. Significant numbers have been taken for the aquarium trade. Despite these problems, boto are still abundant in many parts of their range. Superstitions surrounding this species provide protection from hunting in many areas of its range.