Ganges and Indus Dolphin: Platanistidae
GANGES AND INDUS DOLPHIN: Platanistidae
The single member of this family is a dolphin that lives in freshwater rivers on the Indian subcontinent. At one time, scientists thought that there were two species in this family, the Indus river dolphin and the Ganges river dolphin. However, recent genetic testing shows that even though these groups are separated geographically, they are the same species. Native people call these dolphins "susu," which sounds like the noise they make when they breathe.
Ganges and Indus river dolphins are small, gray-brown dolphins. Adults measure between 5 and 8 feet (1.5 to 2.5 meters) and weigh between 150 and 200 pounds (70 to 90 kilograms). These dolphins have a long beak, or snout, and when they close their mouth, their sharp front teeth are still visible. They use these teeth to catch their prey, animals they hunt for food, mainly fish. Ganges and Indus river dolphins have a small hump behind the center of their back instead of a dorsal (back) fin. Their flippers are broad and paddle-shaped, and their blowhole is a single slit, set off-center on the top of their head. Unlike other dolphins, the opening to their ear is below their eyes.
Ganges and Indus river dolphins have poorly developed eyes. They are able to see only light and dark patterns, which is why they are sometimes called blind river dolphins. Instead of relying on sight to find food, they use a system called echolocation (eck-oh-loh-KAY-shun). Dolphins make sounds (scientists disagree about how this is done) that seem to be focused through the melon, a lump of fatty tissue in the dolphin's forehead, and skull and then sent out into the environment. When the sounds bounce back, the echo is passed through special tissue in the lower jaw to the inner ear. From the time it takes to collect the echoes, their strength, and their direction, dolphins construct a "sound picture" of their environment. This process is so sensitive, that they can "see" an object the size of a kernel of corn at a distance of 50 feet (15 meters), and can find their way around muddy waters as well as clear waters. Ganges and Indus river dolphins also use sound to communicate with each other.
The Ganges and Indus river dolphin is found only on the Indian subcontinent. Indus river dolphins live in about a 100-mile (160-kilometer) stretch of the Indus River where it flows through the Sind and Punjab provinces of Pakistan. Their distribution is limited by two dams built in the 1930s.
Ganges river dolphins live in the Ganges, Meghna, Brahmaputra, and Karnaphuli Rivers, and their tributaries (streams that flow into these rivers). These rivers flow through western India, Nepal, Bhutan, and Bangladesh. The dolphins' range has been reduced, and populations have been fragmented or separated from each other by the construction of dams and water control projects, especially along the Ganges River.
Ganges and Indus river dolphins have developed an unusual method of swimming on their side with their tail held slightly higher than their head. As they swim, they drag one flipper along the bottom to stir up food. Scientists believe that this is an adaptation that allows them to live in water as shallow as 3 feet (1 meter) deep. While swimming like this, these dolphins sometimes carry their young on their back.
These dolphins live in freshwater rivers from sea level to an elevation of 820 feet (250 meters). They can be found in clear, swift-moving water or muddy, cloudy water. They are often found where streams feed into the main river or where there are eddies, which are currents in the water that run opposite the main current. These river dolphins prefer living in water 10 to 30 feet deep (3 to 9 meters), but they are able to live in water as shallow as 3 feet (1 meter). They can survive a wide range of water temperatures, from about 46 to 91°F (8 to 33°C).
Ganges and Indus river dolphins eat bottom-dwelling fish such as carp and catfish, and occasionally shrimp and clams. In captivity they eat from 1 to 3.3 pounds (0.5 to 1.5 kilograms) of fish daily.
BEHAVIOR AND REPRODUCTION
Unlike some social dolphins, Ganges and Indus river dolphins swim alone or with one or two other dolphins. Adults rarely leap out of the water or expose much more of their body than their beak (snout) and melon. Compared to other dolphins, they swim slowly, although they are capable of short bursts of speed. Ganges and Indus river dolphins use echolocation to find their food and navigate around objects in the river. They also communicate with each other frequently through pulses of sound.
Not much is known about the reproductive behavior of these dolphins. Pregnancy is believed to last eight to eleven months. Newborns are about 3 feet (1 meter) long when they are born, and weigh about 17 pounds (7.5 kilograms). It appears that births occur throughout the year. Scientists are not certain, but they think the young nurse anywhere from two months to one year. These dolphins are capable of living long lives and do not become sexually mature (able to reproduce) until they are about ten years old.
GANGES AND INDUS RIVER DOLPHINS AND PEOPLE
River dolphins live in rivers that run through heavily populated and extremely poor areas. These dolphins are sometimes hunted for their oil, which is used in folk medicines for humans and livestock. Occasionally dolphin meat is eaten, and it is often used as bait to attract other fish. Dolphins are also accidentally trapped and drowned in fishing nets. Human development, such as dam building, water control projects, and pollution have all decreased the river dolphin population.
River dolphins are Endangered, facing a very high risk of extinction. There may be fewer than one thousand individuals remaining in the Indus River, while the outlook is equally grim in other river systems, including the Ganges River.
River dolphins are threatened mainly by human development. Dam building, begun in the 1920s, still continues today. Not only do dams isolate groups of dolphins, they interfere with migration and water flow. Heavy fishing, reducing water flow, and preventing flooding all decrease the population of fish that are the main source of food for these animals. In addition, pollution puts a strain on their health and may shorten their lives. Hunting and "accidental intentional" killing of dolphins in fishnets also are threats to their survival.
To combat the decline in population, the Whale and Dolphin Conservation Society recommends establishing protected habitats, training local people to manage river dolphins as a protected resource, educating the public to substitute other oils for dolphin oil, and enforcing protection laws already in existence.
FOR MORE INFORMATION
Carwadine, Mark, and Martin Camm. Smithsonian Handbooks: Whales Dolphins and Porpoises. New York: DK Publishing, 2002.
Gowell, Elizabeth T. Whales and Dolphins: What They Have in Common. New York: Franklin Watts, 2000.
Mead, James G., and Joy P. Gold. Whales and Dolphins in Question: The Smithsonian Answer Book. Washington, DC: Smithsonian Institution Press, 2002.
Smith, Alison M., and Brian D. Smith. "Review Status and Threats to River Dolphins and Recommendations for Their Conservation." In Environmental Reviews. Vol 6, edited by T. C. Hutchinson. Ottawa, Canada: NRC Research Press, 1998, 189-206.
American Cetacean Society. http://www.acsonline.org (accessed on July 8, 2004).
Whale and Dolphin Conservation Society. http://www.wdcs.org (accessed on July 8, 2004).