Amazon river dolphin (Inia geoffrensis)

The Amazon river dolphin (Inia geoffrensis), also known as the boto (pronounced 'boatoo'), bufeo, or pink river dolphin, is a species of dolphin native to the freshwater rivers of South America, particularly the Amazon and Orinoco river basins. They are characterised by their distinctive pink coloration, which is more pronounced in adults and often fades with age. Amazon river dolphins have a flexible neck and long snout, which allows them to navigate through the flooded forests and shallow waters of their habitat. They are known for their intelligence and social behavior, often living in groups called pods. The Amazon river dolphin face threats from habitat loss, pollution, and fisheries, which have led to declines in their populations in some areas.

Physical description

Color: Amazon river dolphins are most commonly associated with a pink hue, though they can range from gray to pinkish-gray. This pink coloration is more prominent in adults and tends to fade with age.
Size: It’s the largest species of river dolphin, with adult males reaching up to 160 kilograms (353 lb) and 2.55 metres (8.36 ft) in length and adult females reaching 1.96m(6.43 ft) in length and 96.5kg (213 lb).^[1]
Body Shape: Their bodies are robust and streamlined, with a long snout and a distinctive bulbous forehead, known as a melon. This shape aids in echolocation, which they use to navigate murky waters and locate prey.
Fins and Flippers: Amazon river dolphins have long, paddle-shaped pectoral fins (flippers) that they use for steering and maneuvering. Their dorsal fin is relatively small and triangular in shape. Their tail fluke is large and powerful, aiding in propulsion through the water.
Teeth: They have long, sharp teeth that are conical in shape. These teeth are well-adapted for catching and grasping prey, primarily fish and crustaceans.
Eyes: Their eyes are small in comparison to their body size and are adapted for seeing in the often murky waters of the Amazon basin. Their vision is likely not their primary sense, as they rely more on echolocation.
Sexual Dimorphism: Adult males are generally larger and bulkier than females, with more pronounced melons on their foreheads.
Skin: Their skin is relatively smooth and often appears shiny. It lacks the typical dorsal ridge found in other dolphin species.

Distribution

The Amazon river dolphin inhabits various river systems across South America. They are found in the Amazon and Orinoco river basins, spanning several countries including Brazil, Bolivia, Colombia, Ecuador, Peru, and Venezuela.^[2]

Brazil

In Brazil, Amazon river dolphins have been extensively recorded. They are found in the central region, particularly in the Araguaia-Tocantins River basin, and various tributaries such as the das Mortes and Verde, Paranã, Vermelho, Peixe, Crixas-Açú, and Água Limpa rivers. Additionally, sightings have been reported in Lake Montaria in the state of Mato Grosso and mangrove habitats in Marajó Bay.^[2]

Amazon river dolphin sightings have also been documented in several rivers and tributaries of the Amazon basin in Brazil, including the Juruá, Purus, Madeira, Tapajós, Xingu (only below Belo Monte falls), Içá, Caquetá-Japurá, Negro-Branco, and Trombetas. Moreover, they have been observed along the Madeira mainstem above and below the Teotônio rapids.^[2]

Bolivia

Reports of Amazon river dolphin sightings come from various river basins in Bolivia, including the Beni (and Orton tributaries), Iténez or Guaporé Basin (Verde, Machupo, and Iporuporé tributaries), and Mamoré Basin and its tributaries such as Pirai, Grande, Ichilo, Chapare, Ibaré, Matucaré, Tijamuchi, Apere, Yacuma, and Yata.^[2]

Colombia

In Colombia, Amazon river dolphins are found in both the Orinoco and Amazon systems. They inhabit the Caquetá-Japurá River, from the Araracuara rapids to the mouth of the Apaporis River at the border with Brazil, the Putumayo-Içá River from Puerto Leguizamo to the east, and in the Amazon River. In the Orinoco, sightings have been reported in various rivers including Meta, Arauca, Casanare, Bita, Vichada, Tomo, Tuparro, Orinoco, Guaviare (and the Guayabero affluent), Inírida, and Atabapo.^[2]

Ecuador

Amazon river dolphins are widely distributed in Ecuador, particularly in the main rivers and some lacustrine systems at elevations below 260 meters. They have been sighted in rivers such as Payamino (near Napo River), Napo, Pastaza, Tigre, and Santiago. Notably, they are absent from the Morona River in the Ecuadorian Amazon.^[2]

Peru

In Peru, Amazon river dolphin can be found in various tributaries of the Ucayali and Marañon flowing generally north, as well as in the Napo, Tigre, and Pastaza tributaries flowing generally south.^[2]

Venezuela

In Venezuela, Amazon river dolphins occur in the Orinoco system, including the delta region upstream at Ciudad Bolivar, Caicara del Orinoco, and near Puerto Ayacucho. They are also found in rivers such as Apure, Portuguesa, Guanare, Guaritico, Capanaparo, Cinaruco, and Caura. Amazon river dolphin sightings have been documented in the Cassiquiare Canal, connecting the Orinoco with the Negro River, and above and below the two sets of rapids at Puerto Ayacucho.^[2]

Threats

Populations of the Amazon river dolphin are at risk because of several threats to the Amazon-Orinoco aquatic ecosystems including residential & commercial development, energy production, mining, pollution, agriculture, hydroelectric development, deforestation and fisheries.^[1]^[2]

IUCN Red List assessments

2018 — Endangered (EN)
2011 — Data Deficient (DD)
2008 — Data Deficient (DD)
1996 — Vulnerable (VU)
1994 — Vulnerable (V)
1990 — Vulnerable (V)
1988 — Vulnerable (V)

Sub species

Inia geoffrensis geoffrensis (Amazon River Dolphin): This subspecies is found in the Amazon River and many of its tributaries.^[3]
Inia geoffrensis boliviensis (Bolivian River Dolphin): This subspecies is found in the Madeira River, a tributary of the Amazon, in Bolivia.^[3]
Inia geoffrensis humboldtiana (Orinoco River Dolphin): This subspecies is found in the Orinoco River basin.^[3]