Indus river dolphins are light brownish-grey, though they sometimes exhibit lighter undersides. They have a long thin rostrum with many long teeth that are visible even when their mouths are closed. Their dorsal fin is rather small compared to other river dolphins, and is more like a triangular hump. They have large flippers and flukes, and flexible necks.
This species is functionally blind. Therefore, like other dolphin species, it relies heavily on echolocation to navigate and hunt1, 13. Externally, the eye appears to be barely larger than a pinhole, restricting light from reaching the retina, there is no lens, and the optic nerve is very narrow, leading scientists to conclude that their eyes are incapable of forming clear images, but that they may still serve as light receptors13.
Indus River Dolphin. Illustration by Uko Gorter
Reproduction and growth
Indus river dolphins reach sexual maturity when they are approximately 10 years old14. Mating occurs throughout the year but births appear to peak between March and May1. After a gestation period of 8-9 months, a single calf is born, generally around 70cm in length, and feeds on milk from the mother14. They can grow up to 2.5 metres in length and weigh 70-110 kg. Limited data is available about their lifespan, but the oldest known animal was 39 years3.
The Indus river dolphin eats a large variety of prey including river prawns, catfish and carp1.
Indus river dolphin. © Nyal Mueenuddin / WWF-Pakistan
Like Ganges river dolphins, Indus river dolphins have developed a unique side swimming behaviour which is an adaptation to help them navigate through shallow waters13. Although the dolphins have occasionally been found in groups consisting of as many as 30 individuals, they are mainly solitary15.
Individuals are at the surface for only about 1 second, and they then dive for just over a minute15. Like other dolphin species, they navigate using echolocation, but reflecting the complexity of the river environment, Indus river dolphins emit sound almost constantly. Generally, these animals are shy towards humans.