Indus river dolphin

The Indus river dolphin (Platanista minor) is a special kind of freshwater dolphin that lives only in the rivers of the Indus basin in Pakistan and parts of northwestern India. It was the very first dolphin discovered that swims on its side. In Pakistan, these dolphins can be found in the Indus River, but they are split into five small groups because of dams built for irrigation. In India, there is a tiny group of them in the Beas River, and they are in big danger of disappearing forever.

For many years, from the 1970s until 1998, people thought the Indus river dolphin and the Ganges River dolphin were two different kinds of animals. But in 1998, scientists decided they were actually two versions of the same animal, called the South Asian river dolphin. However, newer research shows that they are probably different kinds of dolphins after all.

The Indus river dolphin is very important to Pakistan—it is the country’s national mammal. It is also the official aquatic animal of the state of Punjab, India. These dolphins help scientists learn about the health of the rivers they live in, showing how well the water is keeping all kinds of animals safe.

Taxonomy

The Indus river dolphin was first described in 1853 by Richard Owen. He called it Platanista gangetica, var. minor after looking at a dolphin skull that was smaller than the skulls of the Ganges river dolphin.

At first, the Indus and Ganges river dolphins were thought to be the same species, named Platanista gangetica. In the 1970s, scientists decided they were different species, but in the 1990s, they were grouped together again. Now, newer studies looking at genes, how long ago they separated, and skull shapes show that they are indeed two distinct species.

The Ganges river dolphin separated from the Indus river dolphin around 550,000 years ago during the Pleistocene.

Description

The Indus river dolphin has a long, pointed nose, like other river dolphins. Its teeth are visible in both the upper and lower jaws, even when its mouth is closed. Young dolphins have long, thin, curved teeth, but as they grow older, the teeth change into flat, square, bony disks.

This dolphin cannot see clearly because it lacks a special part in its eyes called a crystalline lens, so it is effectively blind. Instead, it uses a special sense called echolocation to find its way and hunt. Its body is brownish and sturdy in the middle, with a small triangular bump instead of a dorsal fin. The flippers and tail are thin and large compared to its body, which measures about 2–2.2 meters (6 ft 7 in – 7 ft 3 in) for males and 2.4–2.6 meters (7 ft 10 in – 8 ft 6 in) for females. The oldest known Indus river dolphin was a male that lived to be 28 years old and measured 199 centimeters (78 inches) long.

Distribution

The Indus river dolphin lives in the Indus River system. In the past, it could be found along about 3,400 km (2,100 mi) of the Indus River and its smaller rivers. Today, it is only found in about 690 km (430 mi) of the main river, and it is no longer in the smaller rivers. A small group still lives in the Beas River and Harike Wetland in Punjab, India.

There are very few of these dolphins left. In 2017, scientists thought there were about 1,800 left. Some surveys have found more, but numbers are still very low.

Behaviour and ecology

The Indus river dolphin is believed to swim on its side. This helps it move easily through shallow waters, especially during the dry season.

Threats

The Indus river dolphin faces many challenges from human activities. Getting caught in fishing nets can hurt the dolphin population. Some dolphins are still caught for their oil and meat, which some people use for medicine or as bait for catfish.

Irrigation projects have lowered water levels, and water pollution from chemicals may also be affecting their numbers. Building many dams on rivers separates dolphin groups and makes it harder for them to find mates. There are three groups of Indus river dolphins that might survive if they are protected. The group living in the Beas River is threatened by heavy fishing, which reduces their food and also leads to dolphins getting caught in nets.

Conservation status

The Indus river dolphin is very rare and needs protection. It is listed as Endangered, meaning there are not many left. Special rules help keep it safe, and scientists are studying it with satellites to learn more.