Description & Behavior
Amazon river dolphins, Inia geoffrensis (Blainville, 1817), aka boutu, boto, bufeo, Delphinorhynchus geoffroyi (Lesson, 1827), Delphinus (Delphinorhynchus) geoffrensis (de Blainville, 1817), Delphinus (Delphinorhynchus) geoffroyi (Desmarest, 1822), Delphinus amazonicus (Spix & Martius, 1831), Delphinus frontatus (G. Cuvier, 1823), Delphinus geoffrensis (de Blainville, 1817), Delphinus geoffroyi (Spix & Martius, 1831), Delphinus geoffroyi (Desmarest, 1822), Delphinus inia (Rapp, 1837), Delphinus rostratus (G. Cuvier, 1812), Inia amazonicus (Pelzeln, 1883), Inia geoffroyensis (Austin, 1897), Inia geoffroyi (Bates, 1863), Inia geoffroyii (Gray, 1846), Inia humboldtiana (Pilleri & Gihr, 1978), and Sotalia pallida (Sanborn, 1949), are one of the few species of fresh water dolphins and the most well-known river dolphin. They are a medium size dolphin with long beaks, a stocky body, and prominent forehead. Males measure about 2.5 m in length; females average 1.8 m with a maximum length of 2.4 m. Amazon river dolphins weight up to 160 kg. They have long beaks with 24-34 conical and molar-like teeth. The conical teeth in the front of the mouth are used for holding prey, the molars in the rear of the mouth are used to grind food before swallowing. A characteristic unique to the Amazon river dolphin is stiff hairs on the beak; the hairs are a sensory organ that help sense prey in muddy river bottoms.
Another interesting characteristic is that Amazon river dolphins are able to move their neck unlike other dolphin species that have fused vertebrae. Neck mobility enables the Amazon river dolphin to look to the side or down. They are also known for their keen eyesight and hearing.
Amazon river dolphins are known as the “pink dolphins” although they range in color depending on their age. Juveniles are dark gray on the dorsal side, lighter gray on the ventral side. As they mature, the ventral side and flanks turn pink making these creatures almost mystical. They become lighter with age, tinged with white and blue-gray coloring.
Unlike other dolphin species, they have no dorsal fin, but they do have a dorsal ridge. The flippers and flukes are large, likely used for maneuvering in shallow river waters.
Amazon river dolphins are often found singly or in pairs. They are a gregarious species unafraid of boats. Like other dolphin species, they are equipped with audible sonar, which is used for echolocating prey.
World Range & Habitat
Amazon river dolphins, Inia geoffrensis, are found in South America from the Amazon river delta to the Andes Mountains. They can also be found in tributaries of the Amazon, lakes, and in the Orinoco River and its tributaries in Venezuela. They also inhabit rivers in Columbia, Ecuador, northern Peru, Brazil, and Bolivia. The species varies in physical characteristics by region causing some scientists to recommend reclassifying the species into subspecies. The only other dolphin that inhabits the range of the boto is Sotalia. This latter species is much smaller and has a taller dorsal ridge.
Feeding Behavior (Ecology)
Amazon river dolphins, Inia geoffrensis, feed on a large variety of fishes, generally near the bottom including Amazon catfish as well as other river fish including piranhas and crustaceans. Some of their prey have hard outer shells, and dolphins have been observed breaking up their larger prey before swallowing. They sometimes feed together and occasionally with Sotalia.
Male Amazon river dolphins reach sexual maturity at about 2 m, females at about 1.7 m. Calves are born between July and September following a 9-12 month gestation period. Newborns measure 80 cm in length and weigh about 6.8 kg.
Conservation Status & Comments
South American Indian folklore hails the Amazon river dolphin, Inia geoffrensis, as sacred leading to the belief that hunting and killing them would bring bad luck, therefore the dolphins were somewhat protected. The arrival of new settlers ended that protection as numerous Amazon river dolphins were killed for their skin for leather and fat for cooking. Several hundred of this species have been captured for live display in aquariums, including at least 100 taken by the US. Unfortunately, few were able to adapt to captivity. They are threatened by various activities, among them are incidental catches in fisheries, damming of rivers associated with hydroelectric development, deforestation, and pollution from mercury mining operations. Despite these problems, these beautiful creatures are still abundant in many parts of their range.
References & Further Research
ACS boto (Amazon River Dolphin) Cetacean Fact Sheet – American Cetacean Society
Jefferson, T.A., S. Leatherwood, and M.A. Webber, FAO species identification guide, Marine mammals of the world, Rome, FAO. 1993. 320 p. 587 figs.
Whale and Dolphin Conservation Society (WDCS)
Balcomb, Kenneth, and Stanley Minasian, The World’s Whales. Illustrated by Larry Foster. New York: Smithsonian Books, W. W. Norton, 1983
Ellis, Richard, Dolphins and Porpoises. New York: Alfred A. Knopf, 1984.
Research Inia geoffrensis @
Barcode of Life BioOne Biodiversity Heritage Library CITES Cornell Macaulay Library Encyclopedia of Life (EOL) ESA Online Journals FishBase Florida Museum of Natural History Ichthyology Department GBIF Google Scholar ITIS IUCN RedList (Threatened Status) Marine Species Identification Portal NCBI (PubMed, GenBank, etc.) Ocean Biogeographic Information System PLOS SIRIS Tree of Life Web Project UNEP-WCMC Species Database WoRMS