River dolphins are found in several rivers in Asia as well as the Amazon basin in South America. They range in size from five to eight feet in length. They are blueish grey in color and can survive in both freshwater and saltwater but prefers freshwater. They are shy, slow swimming. They have very long snouts lined with teeth that they seem willing to use in defense, unlike most dolphins. They swim in small groups with two or three individuals
There are four generally recognized species of freshwater dolphin. The Irrawaddy fresh water dolphin is found in the Mekong River in Laos and Cambodia, the Mahakam River in Kalimantan in Indonesia, and the Yangtze in China. They were once found in the Chao Praya River, which flows through Bangkok, but haven't been seen there in decades (See Laos). The three other live in the Ganges in India, the Indus in Pakistan and the Amazon in South America.
Mark Jenkins wrote in National Geographic: River dolphins parted company with its oceanic ancestors about 15 million years ago, during the Miocene epoch. Sea levels were higher then, large parts of the mainland areas where river dolphins now reside may have been flooded by shallow, more or less brackish water. When this inland sea retreated, some scientists have hypothesized, river dolphins remained in various river basin, evolving into striking creatures that bear little resemblance to our beloved Flipper.[Source: Mark Jenkins, in National Geographic, June 2009]
“At up to 450 pounds and eight feet in length, the Amazon dolphin, or boto, is the largest of the four known species of river dolphin. The others live in the Ganges in India and the Indus in Pakistan, in the Yangtze in China, and in the Río de la Plata between Argentina and Uruguay. All river dolphins are superficially similar, says Hamilton, yet the four species don't belong to the same family. DNA studies by Healy Hamilton of the California Academy of Sciences in San Francisco and others have shown that river dolphins evolved from archaic marine cetaceans (the order that also includes whales) on at least three separate occasions — first in India, later in China and in South America — before modern marine dolphins themselves had emerged as a distinct group. In an example of what's known as convergent evolution, geographically isolated and genetically distinct species developed similar characteristics because they were adjusting to similar environments.
River Dolphin Characteristics
Mark Jenkins wrote in National Geographic: River dolphins “have fat, bulbous foreheads and skinny, elongated beaks suited to snatching fish from a tangle of branches or to rooting around in river mud for crustaceans. The jaw muscles can its elongated beak down on prey with crocodilain ferocity. Unlike marine dolphins, they have unfused neck vertebrae that allow them to bend at up to a 90-degree angle — ideal for slithering through trees. They also have broad flippers, a reduced dorsal fin (a larger one would just get in the way in tight spots), and small eyes — echolocation helps them pinpoint prey in muddy water.
David Attenborough wrote: “The most primitive of tooth whales alive today are the dolphins that swim in some of the world’s great rivers, the Ganges and the Indus, the Yangtze and the Amazon...Their neck bones are still separate so they can move their heads from side to side and the bones in their fingers are still indistinguishable and separate withing the gristle of their flippers.
All dolphins and whales have blowholes about the size of a quarter with inner valves and out outer valves to seal out water when the dolphin is under water. When they surface dolphins inhales four to ten liters of air in one second. They can blow bubbles from their blowholes. Bottlenose dolphins come to the surface an average of once every 28 seconds to breath. In aquariums they have been observed making rings and other shapes with bubbles and playing with them.
Dolphins and whales have hair and blubber — milky, white fat underneath a animal’s skin. Like whales, dolphins have a horizontal fluke rather than vertical tail fins like fish. Dolphins propel themselves forward by moving their fluke up and down. A subdermal sheath is attached to the dolphin’s muscles and skeleton. Dolphins are able to keep their skins clear of parasites that attach to whales through special features in their skins: nanometer-size ripples and ridges with a gel-like coating. Scientists are studying dolphin skin for clues on how to keep ships clear of barnacles and tubeworms
Dolphins have several stomachs, like cows, which may be remnants from its terrestrial ancestors that lives tens of millions of years ago. Dolphins collect salt in their kidneys like camels.
Dolphin Hearing, Noise Making and Echolocation
All toothed whales and dolphins produce sound to communicate, navigate, and locate prey and have a melon, an oval fat-filled organ in their foreheads. A melon focuses outgoing sounds. It evolved from a sac off the main nasal passage for moving air back and forth to create sound vibrations. The lower jaw helps catch returning vibrations.
Dolphins whistle, grunt, squawk and make clicking noises. They make a variety of hissing noises like air escaping from a balloon by blowing air through nasal sacs inside their skull. Most sounds are made in the nasal passages not the larynx. Some believe the clicking noises are generated by forcing air from two sacks near the blowholes. Others believe they are formed by forcing nasal plugs against bony edges of the skull.
Dolphins “hear” using their jaws. They don’t have an outer ear. Instead, sound travels to the inner ear through a thin "window" in the lower jawbone. Clicks can be rattled off at a rate of up to 700 per second or generated as a drawn-out individual sound. The frequency of these clicks varies between 20 cycles per second and 170,000 cycles per second. The human ear can only detect sounds as high as 16,000 cycles per second.
Dolphin click frequency Dolphins — like bats and many whales — use echolocation to locate objects. They make whistles, and ultra-sounds with frequencies of 200,000 vibrations a second with their larynx and produce clicks by forcing air through special passages and sinuses in the heads. The clicks and ultra-sounds pass through the melon, where the clicks are focused, and strike objects outside the dolphin and return to the dolphin brain like radar, enabling a dolphin to determine the distance and certain things about the objects. Blindfolded dolphins can detect a object three inches in diameter from a distance of a 120 meters.
Dolphins rely on echolocation more than sight to sense objects. Not only can they deduce the presence of an object with echolocation they can deduce its size and what it is. They can also determine if a container is full or empty and distinguish between a rock and a piece of flesh. Studies have shown that dolphins are almost as good at picking out objects of different shapes and sizes when they blindfolded as when they are not blindfolded.
River Dolphin Sonar and Communication
River dolphins are nearly blind. They have very small eyes. Indus and Ganges dolphins even lack lenses and can do little more than distinguish light and dark and night and day. The water they swim in is often so muddy that even if the could see they could only see a few inches in front of them.
In the sea, dolphins use their echolocation primarily to locate and catch fish. River dolphins use it primarily to navigate through the murky water so they can sweep for fish. 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."
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.”
Dolphins are among the most vocal animals. They communicate by using body language and at least 30 different sounds and vocalizations. Members of a group can communicate with one another of large expanse of open ocean. They can hear each over of at least half a mile. There are still a lot basic things about dolphin communication that scientists don’t understand: for example how they synchronize themselves when the leap in formation.
Dolphins use unique whistles to identify themselves and make sounds to express excitement and moods and exchange messages that help keep groups together and warn others of danger. Individual identity is practiced by humans and dolphins but few other members of the animal kingdom.
River Dolphin Mating
Mark Jenkins wrote in National Geographic: Vera da Silva have found that female Amazon dolphins in particular stray far into the forest when the Amazon floods during the wet season — perhaps to take refuge from aggressive, bright pink males. The females are mostly gray; the males' pink color, Martin and da Silva believe, is scar tissue. [Source: Mark Jenkins, in National Geographic, June 2009]
Tony Martin of the University of Kent in England has studied Amazon dolphins since the mid 1990s rold National Geographic, "The males beat the hell out of each other. They are brutal. They can snap each other's jaws, tails, flippers, lacerate blowholes. The large males are literally covered with scar tissue." Only a small percentage of males turn bright pink, Martin says, and those are the ones females are most attracted to — at least during the mating season, when the water retreats back into the river channel and both sexes are thrown together.
Being pink is not the only strategy males have for impressing females. They also sometimes pick up weeds or a piece of wood with their beaks, twirl in a circle, and smash the object on the water. Locals long believed the dolphins were just playing, but Martin discovered that only males carried objects, and only in the presence of females. What's more, they were 40 times more likely to get into fights when engaged in such ostentatious behavior. No other mammals besides humans and chimps carry objects for display, says Martin. "It's like a guy showing off — the equivalent of having a Ferrari," he explains.
River Dolphins and Humans
There are stories of how the river dolphins rescued and saved the lives of fishermen and villagers who are drowning or being attacked by crocodiles. According to a Cambodia legend they are descendants of beautiful woman who was forced by her parents to marry a grotesque python. Rather than go through with the marriage she leaped into the river to commit suicide and was transofmedd into a dolphin.
Along the Mekong River there are taboos about catching and eating river dolphins. Even so dolphins suffer from the presence of humans. They get trapped in nets and can’t surface and drown. Fishermen don’t cut the nets because they don’t want the expense of repairing their nets. Conservationist are urging fishermen to switch back to traditionally bamboo nets which don’t endanger the dolphins.
The Khmer Rouge reportedly killed hundred of dolphin in Tonle Sap to discourage superstitions surrounding them and extract oil for machines..
Irrawaddy and Ganges Dolphins
Irrawaddy dolphins are found in the Mekong River in Laos and Cambodia, the Mahakam River in Kalimantan in Indonesia, the Padma River in Bangladesh, the Irrawaddy River in Myanmar, and the Yangtze in China. They were once found on the Chao Praya River, which flows through Bangkok, but haven’t been seen there in decades. The Yangtze river dolphin is considered to be an Irrawaddy dolphin.
The Indus dolphins and the Ganges dolphins live in the Indus River in Pakistan and the Ganges in Nepal, India, and Bangladesh. There are about 500 Indus dolphins left and it t 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.
Mekong River Irrawaddy Dolphin
There are a few dozen freshwater dolphin — the Irrawaddy dolphin—living in the Mekong River. Harmony Patricio told mongabay.com: The dolphin that has a lot of cultural significance.“People really honor the dolphin, and there are many stories about dolphins helping drowning people or helping fishermen to catch fish. So they never kill the dolphins.
T he Mekong River Irrawaddy dolphin (Orcaella brevirostris) population inhabits a 190 kilometers stretch of the Mekong River between Cambodia and Laos. The latest population is estimated between 64 and 76 members (2008 figures). The Irrawaddy dolphin is identified by a bulging forehead, a short beak, and 12-19 teeth on each side of each jaw. The pectoral fin is broadly triangular. There is a small dorsal fin, on the posterior end of the back.
In 2004, the Irrawaddy dolphin was declared a protected species. Most are found around the Khone Falls area in the Mekong River along the Laos-Cambodia border. Some believe they will be extinct in less than 50 years. Many have been killed by gill nets and dynamite fishing used mostly by Cambodians. Some fishermen have purposely caught them for their teeth, which are regarded as talismans against evil spirits Today villagers are encouraged to participate in the tourism trade in the area and so they have reason to conserve the dolphins.
Khon Island near Siphandan (on the Mekong River north of the Cambodian border) is place where tourist gather to try and catch a glimpse of the river dolphins. They are most likely to be seen off the southern tip of the island in the early morning or late afternoon from December to May. The best spot of all is on Kham Island, a small sand island within Cambodian territory on the Mekong River. Boats make runs to this island for a small fee. Viewing the dolphins from boats isn’t really practical because the boats scare the dolphins off.
Irrawaddy Dolphins in Cambodia
The Irrawaddy dolphins found in Cambodia live mainly in the Mekong River around Kratie and Stung Treng provinces. The number of these mammals is estimated to be between 40 and 60 and they are often seen travelling in small groups of 6 to 10 individuals. The females usually give birth to young once every two years most often during the months of June to August. The young dolphins are about 1 meter in length at birth and suckle milk. By adulthood the dolphins can attain a length of over 2.5 meters and weigh up to 180 kilograms. Their diet consists mainly of small fish, shellfish and snails. The dolphins can swim at speeds up to 40 kilometers per hour and stay submerged for periods between five and ten minutes.
The Dolphin Habitat in Kratie, Cambodia is situated at Kampee Village and Resort in the Sambok Commune. Besides being a wonderful tourist hub the Dolphin Habitat, also plays a significant role in the conservation of dolphins. The Irrawaddy Dolphins make their home on a beautiful stretch of the Mekong River near a small set of rapids. They make upward arches, breaking the surface of the water as they swim about the area. The dolphins are most active in the early morning hours (around 6 am) and the late afternoon and early evening hours. A local family hires out their small boat. A young man in the family takes you out on the river for a closer look. The charge is 3,500 riel per person.
The Mekong River Irrawaddy dolphin (Orcaella brevirostris) population inhabits a 190 kilometers stretch of the Mekong River between Cambodia and Laos. The latest population is estimated between 64 and 76 members (2008 figures). The Irrawaddy dolphin is identified by a bulging forehead, a short beak, and 12-19 teeth on each side of each jaw. The pectoral fin is broadly triangular. There is a small dorsal fin, on the posterior end of the back.
In January 2005, four fishermen were arrested in Cambodia after they allegedly killed a rare Irrawaddy dolphin by tossing an explosive device into a river in northeastern Mondulkiri province, officials said yesterday. The 86kg freshwater dolphin was found dead Saturday in the Srepok River after people exploded the device to catch fish, Sam Samat, secretary of the provincial police chief said. "We never knew that there were Irrawaddy dolphins in Srepok River. The fishermen also did not know this kind of animal was in the river," he said, adding that three men and a woman were arrested. Fishing with explosives is common in Cambodia. Fewer than 100 of the famous pink dolphins are left in Asia's Mekong River; once there were thousands. [Source: Agencies, January 28, 2005]
Endangered River Dolphins
Mark Jenkins wrote in National Geographic: “River dolphins have no predators, except for humans. In December 2006 the Yangtze river dolphin, called the baiji, succumbed to pollution, propeller blades, dams, and overfishing; it became the first cetacean to be declared "functionally" extinct — meaning the species cannot renew itself, even if a specimen or two still exist. "Losing the baiji is like taking a chain saw to the cetacean tree of life," says Hamilton. "We've lost 20 million years of independent evolution." The Ganges river dolphin is also in grave danger; only a few thousand remain, and they live in some of the most polluted rivers on Earth. [Source: Mark Jenkins, in National Geographic, June 2009]
“The Amazon species probably has the best prospects; though its numbers are uncertain, Martin thinks at least 100,000 are left. But the trend is worrisome. At the Mamirauá Reserve, Martin's study population has declined by half over the past seven years. Fishermen hunt dolphins for catfish bait, he says, and they also kill them accidentally in their gill nets.
Mekong Dolphin near Extinction, WWF Says
In June 2009. AFP reported: “Pollution in Southeast Asia’s Mekong River has pushed freshwater dolphins in Cambodia and Laos to the brink of extinction, an international conservation group said. The World Wide Fund For Nature (WWF) said only 64 to 76 Irrawaddy dolphins remain in the Mekong after toxic levels of pesticides, mercury and other pollutants were found in more than 50 calves who have died since 2003. “These pollutants are widely distributed in the environment and so the source of this pollution may involve several countries through which the Mekong River flows,” WWF veterinary surgeon Verne Dove said in a press statement. [Source: AFP, June 19, 2009]
The organization said it was investigating how environmental contaminants got into the Mekong, which flows through Cambodia, Laos, Myanmar, Thailand, Vietnam and the southern Chinese province of Yunnan. The WWF said it suspected that high levels of mercury found in some dead dolphins came from gold mining activities. It added that Irrawaddy dolphins in Cambodia and Laos urgently needed a health program to counter the effects of pollution on their immune systems.
Inbreeding among the small population could have also contributed to weakened immune systems of the young dead dolphins, all of whom were under two weeks old. “The Mekong River dolphins are isolated from other members of their species and they need our help,” WWF Cambodia country director Seng Teak said, adding that the mammals “can show remarkable resilience” if their habitat is protected.
The Mekong River Irrawaddy dolphin, which inhabits a 190km stretch in Cambodia and Laos, has been listed as critically endangered since 2004, the WWF said. Thousands of Irrawaddy dolphins once swam in the Mekong. Although regarded as sacred in Cambodia and Laos, their numbers were cut by illegal fishing nets and Cambodia’s drawn-out civil conflict, in which dolphin blubber was used to lubricate machine parts and fuel lamps.
The Mekong is one of only five freshwater habitats in the world for the Irrawaddy dolphin, and Cambodia was thought to support its largest remaining population. With their pale grey skin and blunt beaks, Irrawaddy dolphins resemble porpoises more than their sea-going cousins, and congregate in a handful of the Mekong’s natural deep-water pools.
The Cambodian government has been promoting dolphin-watching to attract ecotourism and cracked down on the use of illegal nets that entangled them. It was hoped that banning fishing nets in dolphins’ protected areas would raise their number to 170 within the next few years.
River Dolphins in the Ganges
The fresh water dolphins of the Indus River in Pakistan and the Ganges in Nepal, India, and Bangladesh are strange creatures. First, 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. Ranging from five to eight feet in length, 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."
Ganges river dolphin reaches lengths of between 2 and 2.6 meters and weighs between 80 and 90 kg. They have a long beak. Its habitat is the Ganges, Brahmaptra, Meghna, Karnaphuli and Sangu Rivers and their tributaries. 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 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.
Endangered River Dolphins in the Ganges
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.
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.
Freshwater Dolphins in China
The baiji, a freshwater dolphin species, is the rarest and most endangered of all whale, porpoise of dolphin species. It lives on a 1,000-mile stretch of the Yangtze river between the mouth of the river and the Three Gorges. They have traditionally been viewed by some as "the Goddess of Chang Jiang" and are a good omen to any fisherman who spots one. The Yangtze river dolphin is considered to be an Irrawaddy dolphin.
Baijis, also known as white flag dolphins or Yangtze river dolphins, weigh between 300 and 500 pounds and reach a length of 8.5 feet. They have a long snout and small eyes and have white sides and a pale blue grayish back. They feed primarily on fish, which they locate with sonar since they are nearly blind.
Baijis can live to be 25 to 30 years of age. They stay under water for an average of 20 seconds and can dive for up to two minutes. They are usually found in pairs or social units of 10 or so members. Some scientists regard them as a subspecies of Irrawaddy fresh water dolphin.
For millions of years river dolphins have inhabited the Yangtze. The first are believed to have migrated up the Yangtze 20 million years ago.
Image Sources: Wikimedia Commons
Text Sources: National Geographic, Natural History magazine, Smithsonian magazine, Wikipedia, New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, Top Secret Animal Attack Files website, The New Yorker, Time, Newsweek, Reuters, AP, AFP, The Economist, BBC, and various books and other publications.
Last updated April 2014