Botos, also called Amazon river dolphins or pink river dolphins, live only in fresh water rivers in South America. They are the largest and most abundant of the river dolphins. Adult botos range in length from 6.6 to 8.5 feet (2 to 2.5 meters) and in weight from about 185 to 400 pounds (85 to 180 kilograms). Males are larger than females. Young animals are usually dark gray. As they mature, their color changes and they become pink. However, individuals that live in dark, muddy water tend to remain darker than those that live in clear water.
Botos have thick bodies and a large slender beak (snout) that contains about 140 teeth. Instead of a distinct dorsal (back) fin, they have a small triangular peaked ridge along their back. Their flippers are large and pointed. Botos are very flexible, allowing them to live in shallow, cluttered environments. One reason for their flexibility is that their cervical vertebrae, or neck bones, are not fused or joined, giving them the freedom to twist and turn their head easily.
Botos have good eyesight both above and under water. However, because they often live in dark, murky water, they usually rely on echolocation (eck-oh-loh-KAY-shun) to avoid objects and find food. The forehead of a dolphin is a lump of fatty tissue called the melon. Dolphins make sounds (scientists disagree about how this is done) that seem to be focused through the melon and skull. These sounds are then sent out into the environment. When the sounds bounce back, the echo is passed through special tissue in the lower jaw to the inner ear. From the time it takes to collect the echoes, their strength, and their direction, dolphins construct a “sound picture” of their environment. This system is extremely sensitive and allows the animal to locate objects very small objects.
Botos are found in the Amazon and Orinoco River systems in Brazil, Bolivia, Colombia, Ecuador, Guyana, Peru, and Venezuela. They require fresh water and do not live in estuaries (EST-yoo-air-eez) where rivers meet the ocean.
Botos live mainly in dark, cloudy water. They seem to prefer areas where water currents meet and cause turbulence. Several studies have found that they are attracted to places where streams flow into the main river channel or to areas around sand bars or sharp bends in the river. Botos live in water with temperatures ranging from about 73 to 86°F (23 to 30°C). During the rainy season (November to May) when rivers flood, they move out of the main river channel into the shallow flooded forests. As the waters go down, they move back into the deeper main channels.
Botos eat a broad range of food, including up to fifty different species of fish. Most of the fish they eat are from 8 to 12 inches (20 to 30 centimeters) long, although they are able to eat fish as long as 31 inches (80 centimeters). During the rainy season, the forests flood, fish swim into the flooded areas to eat seeds and fruits, and botos follow the fish. They are able to move easily in this shallow water, because they are so flexible and they have a well-developed sense of echolocation. When the water level starts to fall, the fish and the botos return to the deeper main channel.
Botos also eat small turtles, mollusks (hard shelled animals like clams), freshwater shrimp, and crabs. Other species of dolphins have only sharp cone-shaped teeth. Botos have this type of tooth, but also have some teeth that are modified for grinding. This allows them to eat a wide variety of food.
BEHAVIOR AND REPRODUCTION
Botos usually swim alone or occasionally with one or two other botos. They communicate with each other using a series of “clicks” that are above the range of human hearing. These communication sounds are not well understood. Botos kept in captivity have been aggressive toward each other, suggesting that in the wild they need to keep a certain distance between themselves and other botos. They are occasionally observed in larger groups when feeding.
Botos swim slowly, sometimes on their backs. They come to the surface to breathe every thirty to sixty seconds, but rarely leap out of the water or even show much of their body above the surface. They are, however, playful and curious. Botos have been seen playing with floating logs or turtles and have been known to come up to boats and rub against them.
Female botos give birth to a single calf after an eleven-month pregnancy beginning when they are three to five years old. After that, they have a single calf every two to five years. Most births occur between May and August, newborns being about 30 inches long (75 centimeters) and weighing about 15 pounds (7 kilograms). They nurse, feed on their mother’s milk, for more than a year. Natural lifespan is estimated at about thirty years. Botos do not appear to migrate.
BOTOS AND PEOPLE
Botos are not hunted, but are sometimes intentionally killed to prevent them from destroying fishing gear. Botos are associated in folklore with misfortune and bad luck.
Although the population of botos in the wild is not known, it is estimated to be in the tens of thousands. Botos are considered Vulnerable, facing a high risk of extinction. The biggest threat comes from human development. In 2000, there were ten dams on the Amazon River that fragmented, or separated, groups of botos and interfered with their free movement. More dams are planned on the rivers that botos inhabit. In addition, water control projects that prevent the forest from flooding during the rainy season reduce food available for fish. This causes the fish population to decrease, meaning the botos will also have less food. Other threats to the boto include mercury pollution from the mining of gold near the rivers, other types of pollution associated with human development, and accidental drowning in fishing gear. Although the boto is protected by law in some parts of its range, enforcement is difficult and not very effective.