Amazon River Dolphin

Inia geoffrensis

FIELD MARKS:

dolphinlike
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to 8 feet
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slightly falcate dorsal fin
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long, distinct beak
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bright pink skin throughout
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Fresh water habitat

Note

One of few fresh water dwelling dolphins. Skin color is pink throughout with varying grayish patches which seem to be different for each individual.

Description

(maximum) Males - 8.4 feet (255cm)/345 lbs. (156.5 kg)
(maximum) Females - 6.6 feet (201 cm)/217 lbs. (98.5 kg.)

Varies between pink and gray. Dependent on age, sunlight, water clarity, temperature, excitement, or a combination of these factors. They are born grey, and become pinker with age. Similarly, individuals found in darker water (where the sunlight cannot penetrate as well) are pinker than those in clear water (where they develop more pigmentation, or a suntan). When excited, they flush to a bright pink color temporarily. This is most visible ventrally on their pectoral flippers and tail, and on their belly. In cold water and at death, pinkness is lost.

Habitat

They are not found in rapids, estuaries, or near waterfalls, but they do range throughout the entire floodplain of the Amazon and Orinoco river systems. They can be found in extremely shallow water during the flooding season. During flooding, their habitat is also filled with trees and plantlife that is normally part of the rainforest floor. This creates an interesting maze of obstacles through which they must weave as they search for their prey. As a result, they are extremely flexible and much slower swimmers than most oceanic species of dolphins.

Range

They are only found in South America, throughout the Amazon and Orinoco Rivers and their tributaries. These rivers flow through seven countries: Bolivia, Brazil, Columbia, Ecuador, Guyana, Peru, and Venezuela. They are a completely freshwater species, never venturing into salt water.

Food

They feed on a remarkably large variety of fish -- over 50 different species -- as well as on crustaceans and occasionally turtles. However, the amount of food eaten is much less than most other dolphin species (0.5% of their body weight compared to 6-10%). This may be related to a lower metabolic rate in Inia made possible by the warm environment of the Amazon and Orinoco river systems.

All dolphins have cone-shaped teeth that are used to grasp fish in their jaws. These animals are unique among dolphins, because they also have molar-like teeth and can chew their prey. Another unique characteristic are the small hairs on their rostrum (or snout) which remain throughout their life. These hairs might be used as a tactile (sense of touch) device when searching for crustaceans in the mud of the river bottom. No other species of dolphin has any hair on its body as an adult.

Comments

Also known as the Boto, Bouto, Pink Dolphin, Inia, or Tonina.

They are far more solitary than many oceanic species. While they are social mammals, they are generally sighted individually or in pairs (most likely mother-calf pairs, based on the size differences). Group sightings appear to be related to mating/courtship, or feeding.

The number of left in the wild has not been determined. It is thought that the population is in good condition, but highly vulnerable because of the destruction of their rainforest environment. The major threats to their survival are the construction of large hydroelectric dams along the rivers, and pollution and deforestation. The fishing industry is not a threat currently, but it is expanding rapidly, and may become a threat.

Some protective legislation exists in the seven South American countries where they are found, but these laws are very difficult to enforce. More legislation (and the means to enforce it) is necessary. Rivers ignore country boundaries and so cooperative efforts between the countries involved is crutial to their protection. Without protection, their survival is seriously threatened.

Credits

Much of the information found here has been adapted from the following sources:

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