The Amazon River basin is home to a unique aquatic mammal known for its unusual coloration. These freshwater dolphins navigate complex river systems, thriving in an environment vastly different from the open ocean. Their distinct appearance and specialized adaptations allow them to thrive in their South American habitats.
Their Common and Scientific Names
These distinctive dolphins are widely known as the Amazon River Dolphin or Boto. They are also called Bufeo or, colloquially, the Pink River Dolphin, reflecting their characteristic hue. Scientifically, they are Inia geoffrensis, within the family Iniidae.
Three subspecies of Inia geoffrensis are recognized: I. g. geoffrensis (Amazon basin), I. g. boliviensis (upper Madeira River, Bolivia), and I. g. humboldtiana (Orinoco basin). While there is ongoing scientific discussion about whether some of these should be considered separate species, they are generally classified as subspecies.
Why They Appear Pink
Amazon River Dolphins are not born pink; young individuals are typically gray and gradually acquire their pink coloration as they mature. This unique color is not due to a specific pigment, but rather the visibility of blood vessels close to the skin’s surface. Their translucent skin allows these underlying networks to show through, similar to how human skin might flush.
Several factors contribute to the varying shades of pink, from mottled gray-pink to bright rosy hues. Older dolphins often exhibit more intense pinks. Physical activity and excitement can also temporarily deepen their color due to increased blood flow, much like blushing in humans.
Dietary carotenoids from fish and crustaceans are thought to influence coloration. Scarring from aggressive social interactions, particularly among males, often heals with a pink appearance. Environmental conditions like water clarity may also play a part, as murky water can help preserve brighter coloration.
Habitat and Conservation Status
Amazon River Dolphins inhabit the vast freshwater systems of South America, primarily the Amazon and Orinoco river basins. Their distribution spans Brazil, Bolivia, Colombia, Ecuador, Peru, and Venezuela. They are well-adapted to their complex aquatic environment, with a flexible neck allowing them to turn their heads up to 180 degrees, aiding navigation through submerged vegetation and flooded forests.
Despite their wide distribution, the Amazon River Dolphin is classified as Endangered by the IUCN Red List. Their populations face numerous threats from human activities. Habitat loss and fragmentation from hydroelectric dams and navigation projects disrupt river connectivity and alter water flow.
Pollution poses a serious risk, particularly mercury contamination from illegal gold mining, as it accumulates in the food chain. Dolphins also face danger from entanglement in fishing gear, especially gillnets, leading to accidental drowning. Intentional killing for bait in certain fisheries or due to perceived competition for fish also contributes to their decline.