Amazon river dolphin

Profile

The Amazon River dolphin is an interesting mammal living, as its name implies, only in the Amazon River. They are one of the few species of dolphins that only live in fresh water. These mammals are also called pink river dolphins and boto. The latter is thought to be from a Portuguese origin, but none of my sources said what it means. The reason for the name pink river dolphin is not easily seen in the picture above, and the one below gives a slightly better view.

It almost looks like that dolphin stayed out in the sun too long. Not all of these dolphins are pink, with some being bluish-gray or white. The younger dolphins are normally gray, with the pink color starting to appear as they mature. This coloring is especially evident in the males.

The beaks, or mouths, of botos are longer and skinnier than those of most dolphins. The beaks can contain up to 140 teeth. These dolphins’ necks are also weird. They are much more flexible than most dolphins’ necks. This is because some of the neck bones aren’t completely connected, so they can turn their head easily in almost any direction.

Size

Amazon River dolphins are some of the smaller dolphins in the world. They can still be somewhat large, but some adults are barely 4 feet (1.2 m) long! The females, which are smaller than the males, can be up to 7.5 feet (2.3 m) long, while the males can grow up to almost 9 feet (2.8 m).

This is a rather large size range, and their weight has a large range as well. The lightest ones still weigh about 215 pounds (98 kg), while the heavier ones can be more than 400 pounds (182 kg)!

Diet

Amazon River dolphins eat fish, but they eat more different species of fish than most other dolphins. They are known to eat at least 43 different species of fish! These fish can range in size from just 2 inches (5 cm) to 44 inches (80 cm) long! These dolphins are definitely not picky eaters.

Not all of their food is fish. Botos will also eat turtles and crabs. During the wet season, the river gets larger, and the fish spread out more. This makes the fish harder to catch, so the dolphins aren’t as picky about what they eat. During the dry season, the river is smaller, so the fish are closer together and easier to catch. At this time the dolphins can choose to eat only the fish they like best.

These dolphins are solitary feeders, not working together to catch prey as some dolphins do. They are most active in the early morning and mid-afternoon. Botos frequently feed near waterfalls or the mouths of tributaries, as the currents here disrupt the fish, making it easier to catch them. Sometimes the disturbances of boats confuse fish enough for the dolphins to catch them.

Habitat and range

Amazon River dolphins live mostly in the Amazon River, but they also inhabit the Orinoco River. This river is connected to the Amazon by a sort of “natural canal.” These animals prefer to live in slower-moving water. During the wet season when the water rises to cover the forest floor, these dolphins will leave the deeper areas and swim through the trees, over what would be land in the dry season.

Status and threats

The IUCN does not currently have enough information to accurately classify this animal, and that is most likely because they are rather rare. Amazon River dolphins are sometimes hunted by fishermen, as their love for fish can be harmful to the fishing industry.

Probably the biggest threat to these dolphins, however, is the use of dams along the rivers they live in. They decrease the supply of fish by preventing migration, and they trap populations of botos, reducing the genetic diversity needed to survive.

Reproduction

Botos breed during the wet season, with the males “proposing” to the females using branches, floating vegetation, or balls of clay. The male will then nibble on the female’s flippers. If she is not receptive, she will respond aggressively.

About 11 months after mating, the female will give birth to a single calf towards the beginning of the wet season, between May and July. In captivity, Amazon River dolphins were in labor for 4-5 hours. The calf is about 30 inches (75 cm) long and weighs a mere 2.5 pounds (1.2 kg). It may be up to 2 years until the mother mates again.

These dolphins do not cope well in captivity, normally living just 3 years. Some have been able to survive more than 25 years in captivity. In the wild, they can live much longer, sometimes as long as 30 years, though the average is closer to 18.

Sources:

Photo credits:

  • Amazon River dolphin – Stephanie Triltsch
  • Amazon River dolphin 2 – Michelle Bender

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