Amazon River Dolphin (Pink Dolphin)

The Amazon River dolphin (also known as the pink dolphin and botos) is a freshwater animal and a species of toothed whale. Considered the biggest and smartest animal of the freshwater dolphin species, it lives in the Amazon, Orinoco and Araguaian rivers located in Bolivia, Columbia, Ecuador, Brazil, Venezuela, and Peru.

River dolphins are smaller than saltwater dolphins, and they have excellent hearing. Pink dolphins must live in warm, shallow water because they have very little blubber. River dolphins suffer in captivity with few aquariums able to keep them alive.

Scientific Name and History

The Amazon River dolphin’s scientific name is Inia Geoffrensis. Its common name comes from where it often makes its home and its skin color.

The name “boto” is used by natives. It is also a popular character in South American mythology, where pink dolphins have amazing musical skills and are seductive. They also love parties. Some myths claim that they can shapeshift into human form and have magical abilities.

There are five extant species besides the Amazon River dolphin: the Tucuxi River dolphin, the Ganges River dolphin, the Irrawaddy River dolphin, the Indus River dolphin, and the Yangtze Finless Porpoise.

It is unknown how or when the dolphin got into the Amazon basin, but it may have done so during the Miocene period, entering from either the Atlantic or the Pacific Ocean before the formation of the Andes.

Species

There is considerable debate within the scientific community as to whether the Amazon River dolphin is actually one, two, or potentially even three different species. In 2014, scientists in Brazil published research in the journal Plot One, saying that the Araguaia River dolphins were a unique species. Also, there has been considerable debate as to whether river dolphins living in Bolivia are a unique species. As of 2020, the IUCN recognizes three subspecies: the Amazon River dolphin (I. g. geoffrensis), the Bolivian River dolphin (I. g. boliviensis), and the Orinoco River dolphin (I. g. humboldtiana).

Appearance and Behavior

The pink river dolphin features that distinctive dolphin smile. They have rounded foreheads and long, slender beaks.

While other river dolphin species, such as the Ganges River dolphin, have dimorphism where females are larger than males, the opposite is true in Amazon River dolphins. Males can grow to be about 50% larger than females and weigh in excess of 400 pounds (180 kg).

The animals have conical-shaped teeth that they use to catch small fish and other prey. The river dolphin features a long nose that can measure up to 23 inches long, and this is about four times longer than the nose of ocean dolphins. River dolphins have a two-chambered stomach, and they breath by emitting air through a blowhole.

Pink dolphins swim with great precision. Because river dolphins are extremely flexible, they can maneuver around rocks, tree trunks and other objects. They also have the ability to swim forward using one flipper while the other flipper paddles backward. This swimming method lets them make tight turns. River dolphins also like to swim upside down.

River dolphins have exceptionally large brains, and while dolphins are known for swimming in groups, river dolphins tend to spend more time alone or among small groups of two to four dolphins. You might see a bigger group of them in areas rich in food.

The Amazon River dolphin does not have a dorsal fin. Instead, it sports a modified hump. The animal makes its way through rivers and flooded areas using strong flippers and a tail fluke. Compared to oceanic dolphins, pink dolphins swim slowly. Their top speed is around 35 miles per hour. The reason for this is that their neck vertebrae are not fused. This gives them more flexibility, but it means that they can not swim as fast. River dolphins are able to turn their heads without shifting their bodies.

River dolphins have unique ear adaptions to help them survive in their watery environment. Dolphins hear sound from their throats instead of from their outer ear to their inner ear. Their ears are also acoustically separated from their heads. Between these two body parts are sinus pockets. The combination gives them enhanced directional hearing under the water. Dolphins use an organ called a melon to emit high-frequency clicks. This allows them to produce biosonar, used to orient themselves.

Dolphins rely on echolocation to the point that they can survive even if blinded. Echolocation lets them determine the size and shape of surrounding objects. In fact, river dolphins have small eyes and have poor vision. Also, their eyes are on the sides of their heads. This means that their vision features two separate views instead of the one forward view that humans see. Researchers believe that some types of pink dolphins are blind while others just have extremely poor eyesight.

These dolphins, like their saltwater cousins, are friendly and curious about humans. That can be a problem, considering their eyesight. Many are killed because they inadvertently come into contact with nets and fishing boats.

Why Amazon River Dolphins Are Also Known as “Pink Dolphins”

One of the defining features of Amazon River dolphins is they often turn pink. Scientists are still researching the reason why, but a few theories stand out.

Amazon River dolphins often fight one another and leave significant amounts of scar tissue. It is hypothesized this scar tissue turns pink, which is why older males tend to have the most distinctive pink coloration.

Amazon River dolphins live in rivers along the Amazon rainforest, which are often inundated with incredible amounts of rain. This high level of rainfall causes the muddy bottoms of rivers to turn a red/pink hue. Amazon River dolphins may have simply evolved to better blend in with their surroundings.

It is important to note that most Amazon River dolphins are born with gray tones, and males tend to become more pink as they age. In addition, this pink coloration normally covers parts of their body while areas of grey remain. It’s hypothesized that males with more pink coloration are better able to attract mates.

Habitat

Amazon River dolphins live in freshwater areas, including lakes, enormous rivers, and small tributaries. As the Amazon is fed by large stretches of rainforest, every year, it floods its banks for extended periods of time. During this period, Amazon River dolphins will expand across the vast inland seas that are created in floodplains.

Pink dolphins can be found in Bolivia, Columbia, Ecuador, Brazil, Venezuela, and Peru. The Amazon River dolphin also lives in the Amazon and Orinoco rivers and in the Araguaia River.

Diet

Amazon River dolphins have teeth that are similar to the molar teeth that humans have. They are not picky about what they eat. The mammals will dine on turtles, shrimp, crabs, and more than 40 different species of fish, including piranhas.

Predators and Threats

Animals that prey on the river dolphin include large snakes, jaguars, and caimans. However, once the species has passed adolescence, they have few natural predators.

Human development and farming have had a major impact on the habitats of the river dolphin. These activities have impacted the ecology of the waterways. Human fishing is also threatening the species. Overfishing is a problem because it decreases food supply. The dolphins also get caught in the nets.

Pollution is another threat. Small gold mining operations cause mercury pollution, and this makes its way to dolphins through the food chain. River dolphins eat a lot of catfish, which dwell on the bottom of waterways where mercury generally accumulates.

Amazon River dolphins are endangered. The Brazilian Institute of Environment and Renewable Natural Resources has taken steps to protect the dolphin species. They have made it illegal for fishermen to kill the dolphins. 

Reproduction, Babies, and Lifespan

In South America, spring is the rainy season. During this time, acres and acres of rainforest floods, turning into an enormous tree-covered sea. The water becomes deep enough for the river dolphins to swim amongst the trees. Mating season occurs when the water recedes, and the male and female dolphins are constricted to the river channels. The dolphin species is polygamous, meaning males mate with several females each year. However, females mate every two to three years.

Female river dolphins are more attracted to males that are a brighter shade of pink. To impress the females, male river dolphins smack the water with bunches of grasses or branches in their mouths. Sometimes, they hold up a turtle to capture the attention of a female. When a female river dolphin becomes pregnant, she will carry the calf for 11 to 15 months. The animal species gives birth to just one calf. After a baby dolphin is born, it will nurse for over a year. Baby dolphins are often around 30 inches long, and they weigh around 22 pounds. Adult female dolphins usually have their calves from July to September. Once they are born, babies remain close to their mothers for protection.

Sexual maturity is based on the dolphin’s size. When a female reaches 5.5 feet in length, she becomes sexually mature. Males reach the stage once they are 7 feet long. In the wild, river dolphins live for an average of 12 to 18 years, but they can live for as long as 30 years.

Population

The Amazon River dolphin population is difficult to estimate because the dolphins live in remote, muddy waters and lack a distinctive dorsal fin that makes it easier to spot them. While their population is thought to be over 10,000, river dolphins are endangered.