Indus blind dolphin, Side-swimming dolphin, Bhulan (Urdu and Sindhi)
The Indus River dolphin (Platanista minor) is a species of toothed whale native to Pakistan and northwestern India. This dolphin was the first discovered side-swimming cetacean. It is patchily distributed in five small, sub-populations that are separated by irrigation barrages. The Indus River dolphin has been named as the national mammal of Pakistan, and the state aquatic animal of Punjab, India.
The Indus River dolphin has the long, pointed nose characteristic of all river dolphins. The teeth are visible in both the upper and lower jaws even when the mouth is closed. The teeth of young animals are almost an inch long, thin, and curved; however, as animals age the teeth undergo considerable changes and in mature adults become square, bony, flat disks. The snout thickens towards its end. The species does not have a crystalline eye lens, rendering it effectively blind, although it may still be able to detect the intensity and direction of light. The body is a brownish color and stocky in the middle. The species has a small triangular lump in place of a dorsal fin. The flippers and tail are thin and large in relation to the body size. Mature adult females are larger than males.
Indus River dolphins presently only occur in the Indus River system, along with a remnant population in the Beas River. A population can be found in the Harike Wetland located in Punjab, India. They prefer a freshwater habitat with a water depth greater than 1 meter (5.6 ft).
Indus River dolphins are active throughout the day. Living in flowing waters, they swim almost constantly with only brief periods of sleep, which add up to seven hours per day. They swim on their sides when in shallow water. River dolphins generally surface with the rostrum, head, and dorsal fin breaking the water and rarely breach or raise the tail fluke, though surface activity can vary based on age, distance from shore, and time of day. Diving may last as long as 8 minutes among adults and subadults; dives of newborns and juveniles are not as long. Indus River dolphins are typically seen alone or in groups of up to 10 individuals, though enough natural resources may attract up to 30 dolphins. Individuals do not appear to have strong social bonds, outside of mothers and calves. Living in shallow river environments with acoustic obstacles, these dolphins echolocate using repetitive clicks spaced 10 to 100 milliseconds apart. Vocalizations used for communication include bursts and twitterings. When hunting at the surface, dolphins listen for the movements of schooling fish which are then herded with spins, side-swimming, and lobtailing. Echolocation signals are not frequently used at the surface, since many fish at this level can hear ultrasound. At the mid-surface level, the dolphins use more echolocation clicks to find prey hidden in clutter and vegetation as far as 20 m (66 ft) away. They flush out bottom-dwelling prey by digging around.
Indus River dolphins are carnivores (piscivores). They feed on a variety of fish and crustaceans, including prawns, carp, catfish, and gobies.
Little information is known about the reproductive habits of Indus River dolphins. Calves have been observed between April and May. Females give birth to a single calf after the gestation period which is thought to be approximately 9-10 months. Indus river dolphin calves are around 70 cm (28 in) long at birth and may nurse for up to a year. They eat their first solid food within a couple of months. Indus River dolphins reach reproductive maturity at around 10 years, though males may not reach their adult size until 20 years.
The Indus River dolphin has been very adversely affected by human use of the river systems in the subcontinent. Entanglement in fishing nets can cause significant damage to local population numbers. Some individuals are still taken each year and their oil and meat are used as liniment, as an aphrodisiac, and as bait for catfish. Irrigation has lowered water levels throughout their ranges. Poisoning of the water supply from industrial and agricultural chemicals may have also contributed to population decline. Perhaps the most significant issue is the building of dozens of dams along many rivers, causing the segregation of populations and a narrowed gene pool in which dolphins can breed. There are currently three sub-populations of Indus dolphins considered capable of long-term survival if protected.
According to the IUCN Red List, the total population size of the Indus River dolphin is 1,987 individuals. Currently, this species is classified as Endangered (EN) on the IUCN Red List but its numbers today are increasing.
