The Amazon river dolphins (known locally as the boto) is the only dolphin species on Earth that turns pink, and the reason has nothing to do with what most accounts suggest. Not pale pink. In older males, a vivid, almost shocking pink that looks less like a natural coloration and more like something that has been dyed. The local name in Brazil is boto cor-de-rosa. Pink dolphin.
The color is real, and the explanation for it is not what most popular accounts suggest.
Inia geoffrensis, the Amazon river dolphins, is the largest river dolphin species on Earth, reaching lengths of up to 2.5 meters and weights of up to 185 kilograms in large males. It is one of only five remaining river dolphin species globally, all of which are endangered or critically endangered, and it is the only one that turns pink.
Why Amazon River Dolphins Turn Pink
The pink coloration in boto is not produced by a pink pigment. It is the result of scar tissue. Botos are highly aggressive animals, particularly males, who engage in frequent and serious fights over females and territory. The repeated scarring from these encounters, combined with the thinness of the boto’s skin relative to marine dolphins, causes scar tissue to accumulate in a way that appears pink against the grey underlying skin.
Older males, who have had more time to accumulate injuries, are pinker than younger males. Females, who fight less frequently, are generally greyer. The degree of pinkness in a male boto is, in a sense, a record of his fighting history, and since fighting success correlates with reproductive success, the pink coloration may function as an honest signal of competitive ability in the same way that other secondary sexual characteristics function in other species.
Researcher Vera da Silva at Brazil’s National Institute for Amazonian Research, who has studied boto biology for decades, has documented the relationship between age, scarring, and coloration in detail. Her long-term population studies in the Amazon have produced the most comprehensive dataset on boto life history available, tracking individuals across years and documenting how their coloration changes as they age and accumulate injuries.
How Amazon River Dolphins Navigate Murky Water
The Amazon River carries an extraordinary load of suspended sediment. Visibility in the water is often measured in centimeters rather than meters. Marine dolphins, which rely heavily on vision for hunting, would be effectively blind in these conditions. The boto has adapted to this environment through an echolocation system of exceptional sophistication.
The boto’s melon, the fatty organ in the forehead that focuses echolocation clicks, is unusually large and flexible relative to marine dolphins. The boto can change the shape of its melon while echolocating, allowing it to direct its sonar beam with a precision that compensates for the visual limitations of its environment. It can detect fish hidden under leaf litter on the river bottom, locate prey inside submerged root systems, and navigate through flooded forest during the Amazon’s annual flood season, when the river expands to cover millions of hectares of forest floor.
The flooded forest is critical to boto ecology. During high water, botos move deep into the forest, hunting fish that have dispersed into the flooded vegetation. Researcher Martin Haimovici and colleagues have documented boto foraging in flooded forest at distances of several kilometers from the main river channel, navigating through submerged trees and vegetation using echolocation alone. When the waters recede, the botos return to the main channels, following the retreating fish.
Amazon River Dolphins Folklore: The Encante
In Amazonian folklore, the boto is a shapeshifter. At night, according to traditional belief, the boto transforms into a handsome man dressed in white who seduces women at riverside festivals and disappears before dawn, returning to the river in his dolphin form. Children born without a known father are sometimes attributed to the boto. The creature is called the encantado, the enchanted one, and it occupies a complex position in Amazonian culture, simultaneously feared, respected, and protected by the taboo against killing it.
This cultural protection has historically provided the boto with a degree of informal conservation that formal legal protection has not always managed to achieve. In communities where the boto taboo is strong, the dolphins are not hunted and are treated with a wariness that keeps humans from interfering with them.
The taboo has weakened in recent decades as traditional beliefs have eroded and economic pressures have increased. Botos are now deliberately killed in some areas to use as bait for a catfish called piracatinga, which is sold commercially. Da Silva’s research has documented this practice and its impact on boto populations, and it has become one of the primary conservation concerns for the species.
The Amazon River Dolphins Under Pressure
Inia geoffrensis was listed as Endangered on the IUCN Red List in 2018, upgraded from Data Deficient as population surveys produced clearer evidence of decline. The primary threats are deliberate killing for bait, entanglement in fishing nets, habitat degradation from dam construction, and mercury contamination from illegal gold mining operations in the Amazon basin.
The Tucuruí Dam in Brazil and the Balbina Dam have already isolated boto populations in the reservoirs they created, preventing genetic exchange with river populations. Planned dam construction across the Amazon and Orinoco systems threatens to fragment populations further.
Da Silva’s population surveys have found significant declines in boto numbers in areas with high fishing pressure and near mining operations. In some stretches of river that were historically abundant with botos, the animals have become rare or absent within a single generation.
The pink dolphins of Amazonian folklore, the shapeshifter who seduces and disappears, is disappearing in a different and less romantic way. The encante is becoming harder to find not because it has returned to the river, but because the river itself is changing around it.