Amazon River Dolphin

## Description

The Amazon river dolphin (Inia geoffrensis ), also known as the boto, bufeo or pink river dolphin, is a species of toothed whale classified in the family Iniidae. Three subspecies are currently recognized: I. g. geoffrensis (Amazon river dolphin), I. g. boliviensis (Bolivian river dolphin) and I. g. humboldtiana (Orinoco river dolphin) while position of Araguaian river dolphin (I. araguaiaensis ) within the clade is still unclear. The three subspecies are distributed in the Amazon basin, the upper Madeira River in Bolivia, and the Orinoco basin, respectively.

The Amazon river dolphin is the largest species of river dolphin, with adult males reaching 185 kilograms (408 lb) in weight, and 2.5 metres (8.2 ft) in length. Adults acquire a pink color, more prominent in males, giving it its nickname "pink river dolphin". Sexual dimorphism is very evident, with males measuring 16% longer and weighing 55% more than females. Like other toothed whales, they have a melon, an organ that is used for bio sonar. The dorsal fin, although short in height, is regarded as long, and the pectoral fins are also large. The fin size, unfused vertebrae, and its relative size allow for improved manoeuvrability when navigating flooded forests and capturing prey.

They have one of the widest ranging diets among toothed whales, and feed on up to 53 different species of fish, such as croakers, catfish, tetras and piranhas. They also consume other animals such as river turtles and freshwater crabs.

In 2008, this species was ranked by the International Union for Conservation of Nature (IUCN) as being data deficient, due to the uncertainty regarding its population trends and the impact of threats. While hunting is a major threat, in recent decades greater impacts on population have been due to the loss of habitat and inadvertent entanglement in fishing lines.

It is the only species of river dolphin kept in captivity, mainly in Venezuela and Europe. It is difficult to train and a high mortality rate is seen among captive individuals.

## Appearance

The Amazon River dolphin, or, otherwise called Boto dolphin is one of the five river dolphins and is the most famous species of the group. The body of this mammal is long and plump, whereas the fins remind paddles by their shape. In addition, the animal can be easily identified by having a ridge on its back instead of a dorsal fin. The Amazon River dolphin also stands out from other dolphin species due to its coloration, ranging from bluish grey to white, and, sometimes, pink. Some vertebrae of the dolphin are unfused, making the neck of the animal amazingly flexible, which allows the dolphin to move its head in almost all directions. The animals have been treated with suspicion by local people. Moreover, the Amazon River dolphin is a subject of numerous myths and tales. According to one of the stories, these animals become handsome men in order to seduce young women, coming to the water.

## Distribution

The Amazon River dolphin is a South American mammal, distributed across the drainage basins of the Orinoco and Amazon Rivers and primarily occurring in rivers and streams with slow current. As the wet season comes, the water level increases, flooding surrounding forests. During this period, the dolphins usually leave the deeper streams to swim through the trees.

## Behavior

The Amazon River dolphins are typically found solitarily as well as in pairs. However, there have been recorded dolphin groups, consisting of up to 15 individuals. The Botos are most active in the early morning and late evening. These animals are neither fast swimmers nor deep divers, often preferring to swim on the water surface. Spotting a boat in the water, these curious dolphins swim up in order to explore it. The Amazon River dolphins are highly communicative animals, sometimes interacting with other dolphin species. Rolling, lob tailing and flipper waving are common behavior among these playful animals. Moreover, they frequently play with their logs as well as pull at underwater grass. Also, these dolphins can often be seen playing with turtles, fish and other aquatic life forms.

## Diet

Amazon River dolphins are carnivores (piscivores). Their diet usually consists of crustaceans, fish and crabs.

## Reproduction

Currently, very little is known about the mating system of these animals. Thus, the dolphins were thought to be monogamous, but recent studies have discovered facts, indicating other types of mating behavior in this species. Males of these dolphins are noticeably larger than females. They display extremely aggressive behavior: because of biting and abrasion, male dolphins often damage their fins, flukes, and blowholes. On the other hand, tooth-raking leads to scarring. The reason of this behavior can be tough competition for mating rights, which brings us to polygynous mating system. In the meantime, they are likely to practice polyandry and polygynandry - a mating system, where both males and females have a number of mates. The breeding period occurs in October - November, while the gestation period lasts approximately 11 months. The female dolphin normally yields a single baby with an interval of up to 5 years. As soon as the baby is born, the mother immediately helps the youngster to come to the water surface for air. The calf is nursed by its mother for about a year after birth, becoming independent within 2 - 3 years. Male dolphins are ready to mate at 7-12 years old, whereas females - earlier - at 6-10 years old.

## Population

### Population threats

Presently, one of the major threats to these animals' population is continued development of the river systems, which are the natural habitat of these dolphins: they suffer from separation of their range into smaller section due to hydroelectric or irrigation schemes, damming rivers. Feeding upon aquatic animals, the dolphins compete with local fishermen. Moreover, the animals are threatened by the fishing process, during which they can accidently be caught in fishing nets or injured because of collisions with boats and motors.

### Population number

According to the IUCN Red List, the total population size of the Boto is unknown for today, but there are estimated populations in certain areas. Thus, in the Amazon basin there are: 107 individuals in the Solimões River (Brazil), 346 the in the Amazon River bordering Peru and Colombia, around 260 individuals in the Mamirauá Lake system of Brazil and 13.000 individuals in the Mamirauá Sustainable Development Reserve. The Orinoco basin holds: 122 individuals in the Apuré River (Venezuela), 14-15 individuals in the Orinoco River (Venezuela) and 8 individuals in the Casiquiare River (Venezuela). Currently, Botos are classified as Data Deficient (DD) on the IUCN Red List.

### Ecological niche

Amazon River dolphins have an important role as predators of the river, and prey on a range of fish species, thus controlling their populations.

## Fun Facts for Kids

The Amazon River dolphin has a very long beak, which can contain up to 140 teeth.

The body of the animal is extremely flexible, helping the dolphin swim even through some very tight areas. The animal is also able to swim upside down: according to some experts, this position promotes better vision, given that the chubby cheeks of the dolphin are an obstacle to seeing downward while the animal is upright.

Due to living in highly murky waters with low visibility, these dolphins have small eyes and low vision.

As the rainy season comes, the Amazon River dolphins move to ponds and lakes, since the rivers are flooded.

They use a wide variety of whistles and clicks as a form of communication.

Not only these highly intelligent animals are capable of identifying potential dangers, related to humans, but they also learn to avoid these threats.

When hunting, these dolphins use echolocation technique: they send out sounds which pass through the water, bouncing from objects, located in front of them and returning to the animal, providing information about the type, size and speed of the potential prey.

## References

https://animalia.bio/amazon-river-dolphin