Not much is really known about the river dolphins living in the Amazon basin. That is why the research of Tamara McGuire and other scientists is so very important. Only with more information about the dolphins can the best possible conservation plan, one that benefits both the dolphins and the people who share their rainforest habitat, be developed.


Which dolphins are we studying and where are they found?

We will be studying two species of river dolphins, the bufeo colorado, often just called, "boto" and the bufeo gris called the "tucuxi". Their scientific names are Inia geoffrensis and Sotalia fluviatilis. Bufeo refers to the sound both species of dolphins make when they exhale.

The Inia, or boto, is found only in South America and ranges throughout the entire flood plain of the Amazon and Orinoco

river systems. These rivers flow through seven countries: Bolivia, Brazil, Columbia, Ecuador, Guyana, Peru, and Venezuela. The boto is a completely freshwater species and never ventures into salt water.

The Sotalia, or tucuxi, is also found in the Amazon and Orinoco basins but is not as widely distributed as the boto. However, the
tucuxi is also found in the marine coastal waters from Panama to the northern part of Argentina.

Only a few rivers in the world have dolphins living in them. The Yangtse River in China, the Ganges River in India and Pakistan, and the Indus River which flows through Nepal, Bhutan, and India all currently have populations of river dolphins. Those populations are declining at a rapid rate however, and in the Yangtse and Indus, the dolphins are close to extinction. Only a few hundred animals remain.


Where do river dolphins come from?

The boto and tucuxi are cetaceans and belong to the same scientific Suborder, the Odontoceti because they have teeth. Scientists think that their recent ancestors are different though. The boto has a long narrow beak and flexible neck and is more closely linked to prehistoric cetaceans. The tucuxi has a more compact shape like a modern marine dolphin. It is thought that the boto has lived in the Amazon basin longer than the tucuxi and is better adapted to the shallow waters.

Because dolphins are mammals, they are warm blooded and
breathe air. Millions of years ago, a land mammal began to adapt to life in the water. Over time, arms became flippers and legs became a tale. The nostrils became a blowhole on top of the head for breathing, making it possible for the dolphins to breathe as soon as their heads break the surface of the water.

Dolphins breathe voluntarily, (unlike humans) which means they must always be partly aware or they would stop breathing and drown. When they rest, one side of their brain stays "awake" so that they can keep breathing. The other side of their brain can go to sleep.

The tables below summarize the two species.



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Inia geoffrensis (boto)

Sotalia fluviatilis (tucuxi)

Common Names

Amazon river dolphin, bufeo, boto


The largest of all river dolphins. Has a flexible body, large flippers and very low dorsal fin.


Adult females: up to 2.4 meters

Adult males: up to 2.8 meters, 150 to 200 kilos

Calves: 70 - 80 centimeters at birth


Bulging head, small eyes and a long beak. There are more than 100 teeth. Some of their teeth are molar-like and they can chew their prey. Boto can turn their heads much further than other dolphins because some of the vertebrae are not fused together. They have 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.


Broad pectoral and tail fins. Low dorsal fin along the back.


Calves are gray at birth. Adults vary form gray to bright pink and some have mixed gray and pink coloring. Some may change color when they are excited.


When they are active, they make loud breathing noises. Underwater they make clicks, creaking noises and squawks.


They swim slowly and only rarely jump clear of the water.


They eat more than 50 species of fish. They also eat crabs in the river banks.


Generally found in groups of only one to five animals.

Life Span

Unknown but some scientists think they may live between 15 and 25 years.

Common Names

tucuxi, delfin gris (gray dolphin)


One of the smallest of all dolphins with a compact body and almost triangular dorsal fin.


Adult average between 1.35 and 1.6 meters and weigh up to 50 kilos. Calves measure between 70 and 75 kilos at birth.


Rounded forehead, dark eyes and a medium length beak with up to 140 teeth. They have a larger brain than the boto in proportion to their size.


Pectoral fins are bigger than average but not as broad as the boto's. Strong, triangular dorsal fin which is often slightly rounded at the top.


They are light to medium gray on top with lighter gray bands on their flanks. When active their pale underside can flush to pink. Some have a white spot or patch on the tip of their dorsal fin.


Short, sharp breathing puffs. Underwater sounds include whistles and clicks.


Fast, active swimmers. They do horizontal, vertical and backward jumps as half somersaults. They also "spy-hop", with their head sticking up out of the water.


They eat twice as much as a boto as they use more energy even though they are smaller.


They can form large groups of 50 or more animals. Generally they are found in groups of two to twenty-five animals.

Life Span


What kind of habitats do river dolphins prefer?

Both species of dolphins live in clear rivers, blackwater rivers, and rivers that are so muddy that you can't see more than a few inches in front of your face. The temperature of the water, however, changes little during the year. The dolphins are limited in their range only by waterfalls, strong rapids, seasonal changes in water level and hydroelectric dams.

In the Amazon basin, rivers may rise and fall by as much as 14 meters over the year. Dolphins remain in the main channels of the rivers during the dry season when tributaries and lakes become too shallow for them to navigate. They can often be seen in the shallow waters along the river banks resting, playing and mating.

When the rains begin to fall and the water levels rise, much of the forest floor is flooded. Fish move into these areas to feed on the fruits and seeds that have fallen from the trees during the dry season. The dolphins also move into these areas. The boto move right in among the trees while the tucuxi stay in the deeper waters. The tucuxi's neck vertebrae are fused so they aren't as flexible as the boto and cannot maneuver between the flooded forest floor.

Regardless of whether it is the dry or wet season though, the dolphins move about throughout each day. They can swim as much as 30 kilometers in any given day. Many individuals do remain in the same general area for years however.


How do river dolphins navigate through the waters and communicate with one another?

Both the boto and tucuxi can see above and below the water but sound is much more important to them as theriver water is often muddy which makes seeing difficult. Using *echolocation, dolphins create "sound" pictures" using a special sonar system. That way they can navigate and communicate with one another even though they may not be able to see in the water.

All species of dolphins use sound for echolocation. Using their melon (the bulbous portion of their forehead), they create a sound that bounces off objects around them. The returning echo of the sound gives the dolphin information about the location and physical description of the object(s). Inia and Sotalia are capable of echolocation, but very little research has been done how they use it.


At what age are river dolphins able to reproduce?

The age at which Inia reach sexually maturity (able to reproduce) is not known. However, by the time males are 198 cm (6.5 ft.) in length and females are 160-175 cm (5.25-5.75 ft.) they are observed to be sexually mature. It is not know if there is a calving season but the *gestation period is 10-12 months. Females can simultaneously *gestate and *lactate, and calves have been known to nurse for over one year. The average length of time that calves nurse is not known.


What is the river dolphins' conservation status?

The boto river dolphin population is listed as Appendix II (threatened) by Convention of International Trade in Endangered Species of Wild Fauna and Flora, 1975 CITES. It is also listed as "vulnerable" by the International Union for Conservation of Nature and Natural Resources (IUCN)/World Conservation Union.
Tucuxi is listed as Appendix I by CITES, and as "insufficiently known" by the IUCN.

The number of Inia and Sotalia left in the wild is not known. It is thought that the populations of both are in good condition for now, but highly vulnerable because of the continued destruction of their rainforest environment. The major threats to their survival are pollution, deforestation, entanglement in fishing gear and competition for fish with human fishers.

Fishing nets are hard for the dolphins to detect and they can become entangled in them and drown. As nets replace traditional methods of fishing more dolphins may get caught. Also, modern fishing methods result in higher numbers of fish being caught. Over fishing may be becoming a problem in some areas as there are less fish for the dolphins to eat.

The human population in the Amazon is growing just like it is in the rest of the world. More and more people are moving into the rainforest for the resources that are available. Sections of forest are cleared, some of which are around lakes and rivers. Clearing areas of trees affects the *watershed and *water cycle. There becomes less food for the fish (and other animals) that feed on the fruit and seeds in the forest. This, in turn, means that there is less food for the dolphins.

Farmers use pesticides that eventually get washed into the rivers, streams and lakes causing water pollution. Oil exploration and the mercury used in gold mining are also causing pollution problems. In some areas, hydroelectric dams are a problem as the dolphins cannot navigate around them and they become separated from other dolphins and their food source.

Some protective legislation exists in the seven South American countries where Inia and Sotalia are found, but enforcement is challenging. More legislation (and the means to enforce it) is necessary, as well as cooperative efforts between the countries involved. Without protection, the survival of the river dolphins is seriously threatened.

Information sources: Tamara McGuire, the Fundacion Omacha, and the Whale and Dolphin Conservation Society. Dolphin artwork by students at St. Theresa School, Oakland, California.

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