SOUTH ASIAN RIVER DOLPHINS
Ganges dolphins (Platanista gangetica) live in the Ganges and related rivers in India, Nepal, and Bangladesh. Indus dolphins (Platanista minor or Platanista gangetica minor) and live in the Indus River in Pakistan and the Beas River of northwestern India . There is some debate as whether they are separate species or more closely related subspecies. There are about 500 Indus dolphins left and it is believed that the concrete barriers that divide the river may interfere with the mammal's ability to breed. Ganges dolphins are better off because their population is spread out over a larger area.
The Ganges and Indus river dolphins are toothed whales classified in the family Platanistidae. The Ganges river dolphin is related to but is much bigger than the much smaller Indus river dolphin. The two species or subspecies split during the Pleistocene, around 550,000 years ago. The earliest fossil identified as belonging to the Ganges species is only 12,000 years old.
The fresh water dolphins of the Indus and Ganges are strange creatures. They are nearly blind. Biologist Kenneth Norris said, "They have very long snouts lined with teeth that they seem willing to use in defense, unlike most dolphins. They swim on their sides and sweep their long bony snouts in wide arcs across the river bottom, emitting long trains of echolocation clicks that let them hunt fish in all but opaque waters."
The Ganges and the Indus river dolphins were initially classified as a single species, Platanista gangetica, but in the 1970s both were split into distinct species. In the 1990s, they were once again grouped together as a single species. More recent studies of genes, divergence time, and skull structure support both being distinct species
Though Indus River dolphins and Ganges River dolphins look very similar have have few physical differences other than for slight differences in tail lengths, the two species are distinguishable by their sizes — with the Ganges river dolphins being significantly bigger — and ranges. Indus River dolphins only inhabit the Indus River system, while Ganges River dolphins live only in the Ganges River system.
Websites and Resources: Britain-based Whale and Dolphin Conservation Society uk.whales.org ; Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Ganges River Dolphins
Ganges river dolphins (Scientific name:: Platanista gangetica) are also known by the name susu in Indoa . They have been recognized by the Government of India as its National Aquatic Animal and is the official animal of the Indian city of Guwahati. The estimated surviving number is 3,000 to 4,000. The dolphins in the Brahmaputra are known locally as “su”. They reportedly swim up the Brahmaputra almost all the way to Assam.
Ganges river dolphins lives along the Ganges-Brahmaputra-Meghna and Karnaphuli-Sangu river systems of Bangladesh and India, and the Sapta Koshi and Karnali Rivers in Nepal. They favor deep pools and seek out eddy countercurrents located downstream of the convergence of rivers and of sharp meanders, and upstream and downstream of midchannel islands. Ganges River dolphins have been reported at densities of 0.7-1.36 dolphins per kilometer. [Source: Wikipedia]
Ganges river dolphins eyes distinguish only between light and dark. They navigate in murky waters using echolocation. The swim slowly but rarely stop. They use their sonar to detect fish and the then snag them with their long beak. Ganges river dolphins often swim on their sides, with their flippers undulating from side to side. The tips graze the bottom for orientation. Using this technique they can move easily in shallow water. The oldest recorded individual was a 28-year-old male, two meters in length. It has estimated they can live up to 30 years old.
Ganges River Dolphin Characteristics and Feeding
Ganges river dolphin reaches lengths of between 2 and 2.6 meters (6.5 and 8.5 feet) and weighs between 80 and 90 kilograms (175 and 200 pounds). Females tend to be larger than males. They have a long, slender beak and a rectangular, ridgelike dorsal fin,
Ganges river dolphins are usually tan, chocolate brown, dark grey or light blue. They have sharp and very pointed teeth, similar to most river dolphins. Their rounded belly and rectangular dorsal fin, makes them look particularly stocky in build compared to other dolphins. Their flippers and tail flukes are large and broad. They have a large melon head used for echolocation. Their eyes are usually small. They are nearly blind and the water they live in is very cloudy. [Source: Wikipedia]
Ganges river dolphins use echolocation to find food. They eat crustaceans such as prawns and fish including carp, mahseer, and even sharks such as the Ganges shark. They may also take birds and turtles. They dolphin do not have a specific mating season. When a calf is born, 8 to 12 months after conception, it stays with its mother for one year.
David Attenborough wrote: “The Ganges dolphin lives in waters that are so cloudy and thick with suspended mud that no one swimming in it, animal or human, could see more than a few inches ahead. The dolphin certainly cannot. For it is blind. Its eyes are tiny and do not even have lenses within them. The animal finds it way around by moving its mobile neck from side to side and making a series of clicking noises. These sounds are very high-pitched and, like those produced by bats, have important components that are far beyond the range of the human ear. They are produced in passages within the skull and then focused, amplified and transmitted forward by a large lump of fat in the dolphin’s forehead, known as the melon. When the beam of these ultra-sounds strikes a hard object, they are reflected back as echoes and received by another lump of fat in the lower jaw, which extends upward towards the dolphin’s ear. So even though the animal is blind, it has a detailed mental picture of its surroundings.”
“The Ganges dolphin feeds in its own peculiar way, tipping on its side and ploughing its flipper through the mud, stirring it up in clouds. As it does so, it greatly increases the frequency of the clicks so that, converted down into our audibility, they sound like the chatter of a machine gun. The effect for the dolphin must be like shining a torch in the twilight and it enables the animal to locate and snap up crabs, shrimp and bottom-living catfish.”
Ganges River Dolphin Behavior and Communication
Ganges river dolphins usually swim alone or in pairs and are not known to do acrobatic maneuvers near boats. Little is known about their behavior because they are usually shy around boats and are hard to observe. They occasionally to breach, but this behavior is rare. [Source: Wikipedia]
Ganges river dolphins are nearly blind. Eecholocation (emitting sound waves and sensing their reflections to determine the location of objects) is used for navigation and locating prey. They show object-avoidance behavior in both the murky waters where they live and in clear water in captivity, demonstrating their echolocation use.
Ganges river dolphins are capable of performing whistles, but rarely do, suggesting that the whistle is a spontaneous sound and not a form of communication. The Ganges river dolphin most typically makes echolocation sounds such as clicks, bursts, and twitters. The pulse trains they produce are similar in wave form and frequency to the echolocation patterns of Amazon river dolphins. Both species regularly produce frequencies lower than 15 kHz and the maximum frequency is thought to fall between 15 and 60 kHz.
Endangered Ganges River Dolphins
A 2017 population assessment estimated that there were less than 3,500 Ganges river dolphins throughout their species' range. The Convention on International Trade in Endangered Species (CITES) places them in Appendix II, which lists species not necessarily threatened with extinction now but may become so unless trade is closely controlled.
Ganges river dolphins are threatened by pollution, gill nets, poaching, dramas and degradation of their habitat. It is believed that the concrete barrages that divide the river may interfere with the mammal's ability to breed. Ganges dolphins are better off than the Yangtze or Irrawaddy dolphins because their population is spread out over a larger area.
Sometimes Ganges river dolphins are killed by local people for their meat or because they are considered a threat to local fishermen, who believe they steal their fish. Soraya Auer and Anika Hossain wrote in The Daily Star of Bangladesh, “Rubaiyat Mowgli Mansur, a dolphin researcher and wildlife photographer, believes some coastal poor people are just unaware of what is right, legal or even ethical. “This winter, we found for the first time an alarming number of people in coastal villages not realising that this thing that was cut up in the markets, that looks like red meat, was endangered dolphin,” says Mansur, referring to the Ganges River Dolphin. “This was really shocking for us but we believe this is a relatively recent development. People are not hunting the dolphins to sell in the market, but rather dolphins get entangled in the fishing nets and then they don't throw them away but sell them to somebody and that somebody cuts it up and takes it to the market.” [Source: Soraya Auer and Anika Hossain, The Daily Star of Bangladesh, July 7, 2012]
“The researcher explains that this discovery is not as bad as in the Jamuna River where there is targeted killing of dolphins so fishermen can extract dolphin oil to use for a special fishing technique. Mansur argues it is more important to influence the village people by raising awareness about the endangered mammals than rushing the police over to arrest them. “It's really worrying but also inevitable as people are becoming poorer and this is meat, so they are going to go for alternative meat sources,” he explains. However, not everyone can claim ignorance of wrongdoing. There is an indefinite number of poachers and traffickers across the country who are more than aware of the illegality of their actions.
Indus River Dolphins
Also known as "bhulans", Indus river dolphins are the national mammal of Pakistan and one of the world’s most endangered marine mammals. . They and Ganges dolphins are regarded by some as the same species — the South Asian river dolphin (Platanista gangetica) — and others as a separate species (Platanista minor or Platanista gangetica minor). From the 1970s until 1998, the Indus and Ganges river dolphins were regarded as separate species. Then they were considered two subspecies of a single species. Now they are viewed as separate species again. The Indus and Ganges river dolphins in turn are different species from the Irrawaddy dolphins found in Myanmar, Borneo, Laos, Cambodia and parts of India.
The Indus dolphin is now found only in the main channel of the Indus River in Pakistan and channels between the Jinnah and Kotri barrages, and in the River Beas (a tributary of the Indus) in Punjab in India. The Ganges dolphin lives primarily in the Ganges and Brahmaputra rivers and their tributaries in India, Bangladesh, and Nepal. There are about 500 Indus river dolphins left and it is believed that the concrete barriers that divide the river may interfere with the mammal's ability to breed. Ganges dolphins are better off because their population is spread out over a larger area. A 2011 survey along the Indus river estimated there were about 1,450 Indus river dolphins remaining at that time. Their lifespan is About 30 years.
According to the World Wildlife Fund: Indus river dolphins are believed to have originated in the ancient Tethys Sea. When the sea dried up approximately 50 million years ago, the dolphins were forced to adapt to its only remaining habitat—rivers. They have adapted to life in the muddy river and are functionally blind. They rely on echolocation to navigate, communicate and hunt prey including prawns, catfish, and carp. [Source: World Wildlife Fund]
Indus River Dolphin Habitat and Where They Are Found
Indus River dolphins live in freshwater and brackish water environments and are found in rivers, streams, canals and estuaries. They are typically found at depths of three to nine meters (10 to 30 feet). The live in waters with a temperature range of 8º to 33º C (8º to 33ºF). [Source: Rachel Bricklin, Animal Diversity Web (ADW) /=]
Today, Indus River dolphins can only be found in the lower parts of the Indus River in Pakistan and in River Beas, a tributary of the Indus River in Punjab, India. They used to range throughout the Indus river system, but now are found mainly in waters above the Kotri Barrage and below the Chasma, Trimmu, Sidhnai, and Islam Barrages. These human-created barriers, in addition to changes in rainfall patterns, have greatly limited the dolphins’ distribution. /=\
Some paleontologists believe that river dolphins might have evolved from marine-dwelling relatives that moved to estuaries and then rivers as seawater levels rose and fell during the Miocene Period (23 million to 5.3 million years ago). Though this species prefers water deeper than three meters, Indus River dolphins have special adaptations such as swimming on their sides that enable them to exist in shallower waters as well. /=\
Indus River Dolphin Physical Characteristics and Feeding
Indus River dolphins range in length from two to 2.5 meters (6.6t o 8.2 feet) and They weigh 60 to 90 kilograms (150 to 200 pounds). Their average weight is 84 kilograms (185 pounds). They are endothermic (use their metabolism to generate heat and regulate body temperature independent of the temperatures around them), There is some sexual dimorphism (differences between males and females): Females are larger than males. [Source: Rachel Bricklin, Animal Diversity Web (ADW) /=]
Indus River dolphins are roughly the same color as the river they live in — gray or brown --- though they sometimes are much lighter on their undersides. Their “beaks” are distinctively swollen at the tip and very long, reaching 20 percent of the length of their bodies, with large, visible teeth.
In contrast to their “beaks”, their dorsal fins are rather small and reduced compared to other river dolphins. Large flippers and flukes, combined with long and remarkably flexible necks, probably help the dolphins navigate effectively. Indus River dolphins have external ears located below their eyes, but their eyes are very small and probably can only see shadowy, unclear images.
Indus River dolphins feed on catfish, herring, carp, gobies, mahseers, prawns, and clams. Captive individuals consume about a kilogram of food each day. These dolphins use echolocation to find prey. They way their body is shaped enables them to pursue prey. Their toothy long snouts are good at snagging prey once it is within range and forage for many bottom-dwelling animals including catfish and invertebrates./=\
Indus River Dolphin Behavior, Perception and Communication
South Asian river dolphins have incredibly poor eyesight. One of their common names is “blind river dolphin”. They rely on echolocation (emitting sound waves and sensing their reflections to determine the location of objects) to find prey such as shrimp and fish, including carp and catfish. Their eyes distinguish only between light and dark. They navigate in murky waters also using echolocation. These dolphins generally do not form tight groups but rather are usually seen on their own or in loose aggregations. [Source: Wikipedia]
Indus River dolphins are motile (move around as opposed to being stationary), solitary and social (associates with others of its species; forms social groups). They appear to migrate seasonally along the river.[Source: Rachel Bricklin, Animal Diversity Web (ADW) /=]
Indus River dolphins are mainly solitary, though the dolphins have occasionally been found in groups consisting of as many as 30 individuals. In general, they travel in groups of no more than three. These dolphins are equipped to swim on their sides in very shallow water if necessary. With the exception of juveniles, Indus River dolphins rarely display the acrobatic and aerial leaping behavior associated with dolphins. However, they are highly vocal and perceive their environment through echolocation as is the case with other dolphins.
Indus River dolphins communicate with sound and sense using touch, echolocation and chemicals usually detected by smell. The sounds they produce are mainly used to navigate while swimming, with a very small percentage used for communication. Their external ears might help receive echolocation signals, which are intermittent pulses rather than continuous whistles. Indus River dolphins are very vocal, but only about five percent of their vocalizations are used in communication. /=\
Indus River Dolphin Mating, Reproduction and Offspring
Indus River dolphins are viviparous, meaning they give birth to live young that developed in the body of the mother, and engage in year-round breeding. Females probably breed once every two years or longer due to their relatively long gestation and nursing periods. The gestation period ranges from eight to 11 months. The weaning age ranges from two to 12 months. On average males and females reach sexual maturity at age 10 years. [Source: Rachel Bricklin, Animal Diversity Web (ADW) /=]
Indus River dolphin calves are born at different times throughout the year which led to the conclusion that these dolphins do not mate seasonally. However, a captive male in Switzerland, chases around two captive females only in the spring.
Indus River dolphins are presumed to give birth to one young at a time. Newborns are about one meter (3.3 feet) long when they are born, which is nearly half the length of an adult female. During the pre-fertilization, pre-birth stage and pre-weaning stages provisioning and protecting is done by females. Calves nurse up to a year after birth. It has been surmised that Indus River dolphin females likely spend much time and invest a lot of energy in the raising of their offspring.
Endangered Indus River Dolphins, Threats and Humans
Their main known predators of Indus River dolphins are humans. They are sometimes hunted by local people for their meat and oil. People in some areas eat dolphin meat, while others use it as a fishing bait. The dolphin’s oil is used for medicinal purposes. It is considered an aphrodisiac and skin treatment. [Source: Rachel Bricklin, Animal Diversity Web (ADW) /=]
Indus River dolphins are classified as “Endangered” on the International Union for Conservation of Nature (IUCN) Red List. The Convention on International Trade in Endangered Species (CITES) has listed them in Appendix I, which lists species that are the most endangered among CITES-listed animals and plants, and Appendix II, which lists species not necessarily threatened with extinction now but may become so unless trade is closely controlled.
Threats include entanglement in fishing gear, habitat degradation, noise, chemical contaminants, and vessel strikes. Indus River dolphins are perhaps most threatened by human-produced dams and barrages. According to the World Wildlife Fund: In Pakistan, their numbers declined dramatically after the construction of an irrigation system, and most dolphins are confined to a 750 mile stretch of the river and divided into isolated populations by six barrages. Their small numbers and divided populations may restrict their gene pool and the sharing of DNA and produce problems associated with low genetic variation within a population. [Source: World Wildlife Fund]
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated June 2023