Species Corner: Amazon River Dolphin

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Species Corner

Amazon River Dolphin (Inia geoffrensis)

 

by Laurie Stepanek

The distinctive pink coloration of the boto, or Amazon river dolphin, makes it easy to distinguish from other odontocetes. Born with dark gray pigmentation, the dolphins become more translucent with age so that blood circulating beneath their skin gives them a vivid pink appearance, especially on the ventral side. Botos living in clear waters tend to have darker pigmentation than those living in turbid waters.

In addition to their unique coloration, botos can be identified by their long beak containing many stiff hairs. Although all dolphins originally have hair, a characteristic of mammals, most lose it soon after birth. Scientists believe that the botos’ hairs are used as tactile sensory organs. These may help make up for reduced eyesight.

The mouth of Amazon river dolphins is fairly straight with a slight upturn at the corners. They have heterodont dentition, with conical front teeth and molar-like rear teeth. They eat a wide variety of benthic organisms, including catfish. Heavily armored fish and crustaceans can be crushed with the rear teeth.

Echolocation is probably a major tool in food-finding and navigation. Botos have the ability to change the shape of their melons, like beluga whales, from flat to bulbous. Also, Amazon river dolphins are often seen "scanning" - turning their heads 90° to the side. This is possible because their cervical vertebrae are unfused, as in many ancestral dolphin species. Besides turning their necks, botos can paddle one flipper forward while paddling the other backwards.

When prey is scattered, as in high-water seasons, botos are generally seen in singles or pairs. During low-water seasons, when prey is more concentrated, botos congregate in groups of about 15. Most births occur between June and September. Some females have been observed as lactating and pregnant at the same time.

Botos move at a slower pace than most marine dolphins, swimming between 1.6 and 3.2 km/hour on average. They have occasionally been observed leaping above the surface. They rarely dive longer than two minutes at a time.

Living throughout the Amazon and Orinoco River basins in Brazil, Peru, Bolivia, and Venezuela, botos were historically safe from capture in much of their range because of superstitions of the native people. Children born with spina bifida, in which the skull fails to close, appear as if they have a blowhole and are known as "boto’s babies." Natives feared that harming a boto will cause their children to be born with this disease.

The species name, Inia geoffrensis, is derived from the name used for botos by a native Bolivian tribe, and from the name of a French naturalist, Geoffrey St. Hilaire. St. Hilaire worked for Napoleon Bonaparte to collect zoological specimens, and his boto specimen serves as the type specimen for the species.

The biggest threat to all species of river dolphins now is land development by humans. Hydroelectric dams limit dolphins’ movements, and pollution causes developmental and other health problems. Some dolphins are captured in fishing nets, or are captured to be put in aquarium displays.

 

Jefferson, T.A., S. Leatherwood, and M.A. Webber. FAO Species Identification Guide: Marine Mammals of the World. FAO. Rome. 1993.

Leatherwood, S. and R. Reeves. The Sierra Club Handbook of Whales and Dolphins. Sierra Club Books. San Francisco. 1983.

Morell, Virginia. 1997. Looking for big pink. International Wildlife. November/December 1997: 26.

 

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Created: May 19, 1998
Updated: May 19, 1998