Indus River Dolphin (Platanista gangetica minor)
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· Indus River dolphins have very small eyes that resemble pinhole openings. Some scientists believe they are functionally blind, sensing only light levels and direction.
The Indus river dolphin is a subspecies of the Ganges river dolphin (Platanista gangetica) .Species Description
Indus River dolphins, sometimes called "bhulans," are one of two separate subspecies of South Asian river dolphins. The other recognizable geographic form or subspecies is the Ganges River dolphins (Platanista gangetica gangetica), also sometimes called "susus." The Indus River dolphin subspecies is one of the world's most endangered cetaceans.
Indus River dolphins are about 7-8.5 ft (2.2-2.6 m) and weigh 150-200 lbs (70-90 kg). The Indus River subspecies is considered slightly smaller than the Ganges River subspecies (Jefferson et al. 2008). Females are slightly larger than males. They have an unusual robust or chunky body with a low triangular "dorsal" fin located far (about two-thirds) down their back. They have a rounded "melon", a very long narrow beak, extremely small eyes, and noticeable external ears. A longitudinal ridge can be found on the melon as well as from the dorsal fin to the tail. The eyes are poorly-developed (lack a crystalline eye lens) and located above the corners of the mouth (Shirihai and Jarrett 2006). These animals have a uniformly gray coloration pattern with a pale white or pinkish underside, giving a slight counter-shading effect. As this species ages and matures, the melon gradually becomes less rounded.
Indus River dolphins are usually found individually or in pairs, but have been occasionally seen in larger groups of up to 10 or more animals. Little information is available or known on the social structure of these groups.
Indus River dolphins' swimming behavior is often described as active, yet timid and reserved. This species is frequently seen swimming on its side, especially when in captivity. When at the water's surface, these animals can breach or just lift their heads and beaks out of the water. "Breaching" may occur as a response to threats and other disturbances (Shirihai and Jarrett 2006).
Indus River dolphins' generally dive for 30-90 seconds, but are capable of holding their breath for up to several minutes. During dives they use their long beaks to probe the sediment along the bottom of the river to feed on prey such as clams, fish, and shrimp. They have 26-39 pairs of teeth in each jaw that are useful for grasping prey. The fang-like teeth in the lower jaw are comparatively longer and curved, and may interlock, overlap, and be visible outside the mouth. As these animals get older, the teeth become worn-down. Groups may coordinate their movements to cooperatively feed on prey.
Indus River dolphins become sexually mature at lengths of about 5.5 ft (1.7 m) or more, and begin breeding between 6-10 years of age. Females give birth year-round to a single calf that is about 2-3 ft (0.7-0.9 m) long. Mothers may also nurse calves for about 1 year before weaning. The estimated lifespan of this species is about 30 years.
Indus River dolphins prefer the fresh and possibly brackish, shallow (usually less than 100 ft or 30 m), murky waters of the Indus River system in Pakistan. This species may occur in the main channels of rivers and in tributaries and lakes during the flood season.
Indus River Dolphin Range Map
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Indus River dolphins occur in the lower and middle areas of the Indus River in south-central Pakistan on the Indian subcontinent. Their current range is about 435-620 miles (700-1,000 km) along the Indus River and its tributaries. Their migrations have been linked to the monsoon. Historically, their range extended from the Indus River delta to the shallow, rocky foothills of the Himalayas (~3,400 km or 2,100 miles). The tributaries this species once occupied include: the Sutlej, Ravi, Chenab, and Jhelum Rivers (Reeves et al. 2002). Today, their distribution and range is extremely limited; it is currently just 20% of its historical extent (Shirihai and Jarrett 2006).
For management purposes, there are five sub-populations (three meta-populations) of Indus River dolphins inhabiting the animal's range on the river. Most of the dolphins in these sub-populations are located between the Chashma and Taunsa, Taunsa and Guddu (Punjab Province), and Guddu and Sukkur "Barrages" (Sind Province) (Reeves et al. 2002). The largest sub-population of this species can be found in south-central Pakistan between the Guddu and Sukkur Barrages, followed by those between the Taunsa and Guddu Barrages (Shirihai and Jarrett 2006; Reeves et al. 2002). Small numbers of individuals are scattered outside of these barrages. A survey along the river in 2001 found at least 1,000 animals throughout the species' range. There are insufficient data available on current population trends.
Indus River dolphins have been incidentally taken as bycatch in fisheries such as gillnets and longlines. These animals have also been targeted and harpooned by local fisherman for bait, medicine, and meat and oil for consumption. Indus river dolphins are affected by human development and other anthropogenic impacts such as hydroelectric dams and irrigation canals (e.g., Indus Basin Irrigation System) that can separate populations, and reduce and alter suitable habitat. Individuals have been entrapped in irrigation canals along the river and its tributaries. They are also susceptible to vessel strikes, and pollutants and other contaminants discharged into the water from agriculture, industrial, and urban use. These contaminants have led to fish kills, which may deplete Indus River dolphins prey. Another threat to this species is water consumption for various uses by humans in Pakistan 's arid climate.
The International Union for Conservation of Nature and Natural Resources (IUCN's) Red List of Threatened Species considers this species "Endangered" due to declining population status and trends.
The World Wide Fund for Nature, Pakistan Office and the United Nations Development Programme (UNDP) have developed programs to rescue trapped Indus River dolphins. Wildlife reserves were created and a hunting ban implemented along the river in Pakistan in the 1970-1980s for the protection and conservation of this species.
|ESA Listing Rule||56 FR 1463||01/14/1991|
- U.S. Fish & Wildlife Service Indus River Dolphin Species Profile
- NMFS National Marine Mammal Laboratory River Dolphin Information
- Jefferson, T. A, M. A. Webber, and R. L. Pitman. (2008). Marine Mammals of the World, A Comprehensive Guide to their Identification. Amsterdam, Elsevier. p. 294-296.
- Reeves, R. R., P. A. Folkens, et al. (2002). Guide to Marine Mammals of the World. New York, Alfred A. Knopf. p. 302-305.
- Shirihai, H. and B. Jarrett (2006). Whales, Dolphins and Other Marine Mammals of the World. Princeton, Princeton University Press. p. 238-239.
Updated: December 12, 2012