The Amazon River dolphin, also known as the boto, is a unique freshwater species inhabiting the extensive Amazon and Orinoco river systems across South America. These captivating creatures are found in countries like Brazil, Bolivia, Colombia, Ecuador, Peru, and Venezuela.
The Amazon River Dolphin: An Overview
The Amazon River dolphin possesses several distinctive characteristics, setting it apart from its marine relatives. Born grey, adults typically develop a striking pink coloration, varying from dull gray-pink to bright flamingo pink, influenced by water clarity, temperature, and excitement. Unlike other dolphin species, it has unfused neck vertebrae, allowing it to turn its head up to 180 degrees. This flexibility, combined with its unique paddling ability, enables them to navigate intricate submerged forests and maneuver around obstacles like tree trunks and roots in search of prey.
They are the largest freshwater dolphin species, with males reaching up to 2.5 meters and weighing over 185 kilograms. They primarily rely on echolocation to navigate and locate food in murky waters, emitting low-powered clicks to avoid overwhelming echoes in shallow, complex environments. As apex predators, Amazon River dolphins play a significant role in maintaining fish populations. Their diverse diet includes at least 53 different fish species, along with river turtles and freshwater crabs, which they can crush with their unique molar-like teeth.
Direct Human Impacts on Survival
The Amazon River dolphin faces severe threats from human activities that cause injuries or fatalities. A major cause of dolphin deaths is bycatch in fishing gear. Dolphins frequently become entangled in nets, leading to drowning because they cannot surface to breathe. Local fishermen may also intentionally kill entangled dolphins, viewing them as competition for fish resources or due to superstitions.
Targeted killing of dolphins for use as bait in the piracatinga (Calophysus macropterus) catfish fishery is another significant human impact. This practice, despite being illegal, provides effective bait for the piracatinga, a scavenger catfish. The demand for piracatinga, particularly in markets like Colombia, has driven this unsustainable practice, contributing to substantial declines in dolphin populations. Brazil implemented a five-year moratorium on piracatinga fishing in 2016, extended until July 2023, but illegal trade and killing persist due to weak enforcement.
Beyond fishing-related mortality, dolphins also experience direct harassment and collisions. Increased boat traffic in the Amazon’s waterways, particularly around dams, can lead to injuries and deaths from collisions. Some local communities may also intentionally harm dolphins due to the perception that they compete for fish, or as a result of traditional beliefs.
Habitat Degradation and Environmental Challenges
Broader environmental issues and habitat alterations also affect the Amazon River dolphin’s survival. Pollution is a widespread threat, with various contaminants impacting their aquatic environment. Mercury contamination, primarily from illegal gold mining, is a serious concern. Mercury from gold extraction enters rivers, accumulates in the food chain through fish, and poisons dolphins as apex predators. Studies show a notable percentage of river dolphins exhibit mercury levels exceeding health guidelines.
Agricultural runoff containing pesticides and industrial waste further pollutes the rivers, posing additional risks to the dolphins and their prey. Plastic pollution, including microplastics and larger debris, also contributes to the degradation of the river system. As forests are cleared along riverbanks, soil erosion increases, leading to more sediment in the water. This sedimentation reduces water clarity, making it harder for dolphins to navigate, find food, and communicate effectively, and disrupts the aquatic food web.
Hydropower dam construction fragments river habitats, isolating dolphin populations and reducing genetic diversity. Dams alter natural water flow patterns, impede fish migration—a primary food source for dolphins—and can lead to localized extinctions. Noise and vibrations during dam construction can also harm dolphins, and the resulting reservoirs change their natural environment.
Climate change introduces challenges through altered rainfall patterns, extreme droughts, and floods. Prolonged droughts, exacerbated by deforestation, lead to low water levels and high temperatures, causing mass dolphin die-offs. Extreme floods can also disrupt their habitats and prey availability. These climate-induced changes not only reduce fish populations but also increase heat stress in dolphins, weakening their immune systems and making them more vulnerable to disease.