Irrawaddy dolphins (Scientific name: Orcaella brevirostris) are lightly colored and similar in appearance to beluga whales. They have a blunt, rounded head, and an indistinct beak. Their dorsal fin is short, blunt and triangular. In the wild, they have been seen spitting out streams of water, a unique and peculiar behavior. Contrary to what some people believe, these animals are not considered true river dolphin, but an oceanic dolphin because they can live in brackish water near coasts, river mouths and in estuaries. Even so they also live a considerable distance upriver in freshwater as they do in the Mekong and Irrawaddy Rivers. [Source: WWF]
Irrawaddy dolphins feed mainly on fish but also eat crustaceans and cephalopods and other things they can find. These dolphins sometimes spit water while feeding, perhaps to herd fish. Other than humans, there are no known natural predators of Irrawaddy dolphins. Otherwise, they are typically considered the top predator in their river ecosystems. [Source: Melissa Koss; Lucretia Mahan; Sam Merrill, Animal Diversity Web (ADW) /=]
According to the World Wildlife Fund: Irrawaddy dolphins enjoys the highest level of international protection. All trade is forbidden, under international agreements. Some Irrawaddy dolphin populations are classified by the International Union for Conservation of Nature (IUCN) as critically endangered. This includes the Malampaya Sound sub-population in the Philippines. Irrawaddy dolphins in general however, are International Union for Conservation of Nature (IUCN) listed as a vulnerable species, which applies throughout their whole range. In 2004, Convention on International Trade in Endangered Species (CITES) transferred the Irrawaddy dolphin from Appendix II to Appendix I, which forbids all commercial trade in species that are threatened with extinction. The Irrawaddy dolphin is listed on both Appendixes I and II of the Convention on the Conservation of Migratory Species of Wild Animals.
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
Irrawaddy Dolphin Habitat and Where They Live
Irrawaddy dolphins are named after the Irrawaddy River in Myanmar bu are also found in the Mekong River in Laos and Cambodia, the Mahakam River in Kalimantan in Indonesia, Odisha, India and the Padma River in Bangladesh. They were once found on the Chao Praya River, which flows through Bangkok, but haven’t been seen there in decades. The baiji (Yangtze river dolphin, Lipotes vexillifer) is considered by some to be an Irrawaddy dolphin. But it looks really different. It has a long slender snout and it is hard to believe it is an Irrawaddy dolphin. In any case it is now believed that the baiji is now extinct.
Irrawaddy dolphins once ranged throughout much of the tropical and subtropical Indo-Pacific region; along the coasts of India, Bangladesh, Myanmar (Burma), Thailand, Cambodia, Laos, Vietnam, Malaysia, Singapore, Brunei and Indonesia. Now they are found in partes of this range. [Source: Melissa Koss; Lucretia Mahan; Sam Merrill, Animal Diversity Web (ADW) /=]
Irrawaddy dolphins prefer coastal areas, particularly muddy, brackish waters at river mouths and deltas, and do not appear to venture far offshore but occupy areas that pretty far upriver where the water is freshwater. They are typically found at depths of 2.5 to 18 meters (8.2 to 59 feet). Most sightings have been made within 1.6 kilometers of the coastline, but some have been reported in waters greater than five kilometers from shore. The oldest recorded Irrawaddy dolphins, all of which were found dead in fishing nets, were estimated to be 28 years old. Several individuals of this age have been found, all entangled in nets, so it is believed that Irrawaddy dolphins can live longer. /=\
Irrawaddy Dolphin Physical Characteristics
Irrawaddy dolphins range in length from 1.46 to 2.75 meters (4.8 to 9 feet), with their average length being 2.1 meters (7 feet). They range in weight from 114 to 133 kilograms (251 to 293 pounds), with their average weight being 124 kilograms (273 pounds). Some sexual dimorphism (differences between males and females) exists: Males are larger, heavier and longer than females. They also have a larger dorsal fin than females. [Source: Melissa Koss; Lucretia Mahan; Sam Merrill, Animal Diversity Web (ADW) /=]
Irrawaddy dolphins are endothermic (use their metabolism to generate heat and regulate body temperature independent of the temperatures around them) and homoiothermic (warm-blooded, having a constant body temperature, usually higher than the temperature of their surroundings). /=\
According to Animal Diversity Web: Unlike other dolphins, Irrawaddy dolphins lack a beak and have flexible necks. The flexibility in the neck causes visible creases behind the head. Additionally, Irrawaddy dolphins have bulging heads, with the forehead extending past the mouth, broad triangular, paddle-like, pectoral fins, and small, triangular dorsal fins set approximately two-thirds of the body length along the back. Skin coloration varies from slate-blue to slate-gray with a lighter underside. The face and head are similar in appearance to beluga whales. Irrawaddy dolphins have narrow, pointed, peg-like teeth about one centimeter in length in both the upper and lower jaws. Irrawaddy dolphins lack a cardiac sphincter and the stomach is subdivided into compartments. /=\
Irrawaddy Dolphin Behavior
Irrawaddy dolphins are diurnal (active mainly during the daytime), motile (move around as opposed to being stationary), sedentary (remain in the same area), and social (associates with others of its species; forms social groups). In terms of home range, Groups of Irrawaddy dolphins inhabit discrete ranges of approximately 35 kilometers in length, based on some observations. [Source: Melissa Koss; Lucretia Mahan; Sam Merrill, Animal Diversity Web (ADW) /=]
According to Animal Diversity Web: Irrawaddy dolphins stay in groups of three to six individuals and are social within their pods. They are also social outside of their group and mixing between groups has been reported. When scouting areas, Irrawaddy dolphins raise their heads out of the water and rotate around to see their surroundings. Irrawaddy dolphins swim slowly and display sluggish movements. When they surface to take a breath, only the top of the head is visible and it is done quickly; only 14 percent of all surfacings between long dives include rolling, splashing, or limb waving and slapping. Before an Irrawaddy dolphin dives, it usually surfaces two times. The longest recorded dive is over six minutes long. /=\
Irrawaddy dolphins in Chilka Lake in Odisha, India are known to swim onto a sand bar and roll around, then retreat if disturbed. Irrawaddy dolphins have also been seen waving or slapping their flippers and tail, breaching or partially leaping from the water, blowing bubbles, rolling sideways, and pausing at the surface. Water spitting has been observed on numerous occasions, but the reason for this behavior is unknown. Local fisherman report that they are able to identify individual dolphins based on unique behaviors./=\
Irrawaddy dolphins sense using echolocation (emitting sound waves and sensing their reflections to determine the location of objects) vision, sound, touch, ultrasound and chemicals usually detected with smelling or smelling-like senses and communicate with vision, sound and chemicals usually detected by smelling. Vocalizations of Irrawaddy dolphins in captivity within the Mahakam River, Indonesia included a single-component sonar signal, with the majority of frequencies captured at 60 kHz. Pulse trains were consistent with rates repeated at 40 to 60 kHz. Researchers theorize that Irrawaddy dolphins have a narrow sonar field. Little is known or recorded regarding courtship communication or other social signals. /=\
Irrawaddy Dolphin Mating, Reproduction and Offspring
Irrawaddy dolphins They are viviparous, meaning they give birth to live young that developed in the body of the mother, and engage in seasonal breeding.Females may not reproduce yearly, in one population females give birth every three years. Irrawaddy dolphins breed in December through June, with the average number of offspring being one. The gestation period ranges from nine to 14 months. The average weaning age is 24 months. Females and males reach sexual maturity at three to six years. [Source: Melissa Koss; Lucretia Mahan; Sam Merrill, Animal Diversity Web (ADW) /=]
Little is currently known about mating behavior of Irrawaddy dolphins. Since the animals live in small groups averaging between three to six individuals, it is presumed that breeding happens outside of those groups. These dolphins are believed to be polygynous (males having more than one female as a mate at one time) as this is often the case with other dolphin species. /=\
The calving season for Irrawaddy dolphins is from June to August for at least some populations. . Captive born Irrawaddy dolphin calves were measured at 96 centimeters (3 feet) in length and weighed 12.3 kilograms (25 pounds). In the first seven months the calves increased in length by 59 percent and 266 percent in weight. From birth to approximately seven months old, calves subsist solely on the nutrition from the mother. Calves begin eating fish around six months and are fully weaned at about two years old. After seven months the calves stay within the pod and continue to receive nourishment from the mother while also eating fish. Adult length is achieved between three and five years old. Rate of sexual maturation is thought to be positively correlated with growth rate. It is presumed the calves learn to prey on fish by copying behavior of the mother's and pod mates.
Based on the behavior of other dolphins it has been inferred that with Irrawaddy dolphins parental care is provided by females. During the pre-fertilization, pre-birth, pre-weaning and pre-independence stage provisioning and protecting are done by females. The post-independence period is characterized by the association of offspring with their parents. There is an extended period of juvenile learning. /=\
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]
Irrawaddy 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..
Endangered Irrawaddy River Dolphins
Irrawaddy dolphins are designated “Critically Endangered: on the International Union for Conservation of Nature (IUCN) Red List. Convention on International Trade in Endangered Species (CITES) lists them in Appendix I, which lists species that are the most endangered among CITES-listed animals and plants.
Humans are responsible for a large number of deaths to Irrawaddy dolphins, who are often caught in nets or harmed by boats or destructive fishing practices (such as, dynamite fishing). Currently, the most immediate threat facing Irrawaddy dolphins is drowning in gill nets. The threat of gill net entanglement occurs primarily during the dry season (December to May), when dolphins settle in deep water pools. Dynamite and electric fishing occur in some important habitats. These activities are causing depletion of the dolphin's fish supply and noise from the explosions is potentially dangerous to dolphins.[Source: Melissa Koss; Lucretia Mahan; Sam Merrill, Animal Diversity Web (ADW) /=]
Due to the small population size and their narrow distribution, it is quite possible that dam construction or river dredging anywhere within their habitat might critically endanger populations. Furthermore, uncontrolled tourism can harass dolphins in important habitats during the dry season and interfere with normal activities, such as feeding, resting, and socializing. Overfishing, collisions with boats and injuries from boat propellers are also threats to their survival. /=\
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.
Freshwater Dolphins in China
For millions of years river dolphins have inhabited the Yangtze. The first are believed to have migrated up the Yangtze 20 million years ago. There is also a species of river porpoise: the finless porpoise. In 1993 2,700 lived in the Yangtze. Less than 1,000 live there now according to an expedition in 2006. So they don't go the same way as the baiji and colony of 30 of them has been established in nature preserve, far from the polluted river. The hope is that they will reproduce.
Baijis (Scientific name: Lipotes vexillifer) are a freshwater dolphin species found in China. They are the rarest and most endangered of all whale, porpoise of dolphin species. They live on a 1,000-mile stretch of the Yangtze river between the mouth of the river and the Three Gorges.
Baiji have traditionally been found in China from the mouth of the Chang Jiang (Yangtze) to a point about 1,900 kilometers (1,200 miles) up the river, as well as in the middle and lower regions of the Quintangjiang River and in the Dongting and Poyang lakes. They prefer to stay near large eddies that form next to sandbars and have been observed in lakes, ponds, rivers, streams as well as estuaries and areas adjacent to rivers and other water bodies. [Source: Allison Poor and Sarah Grigg, Animal Diversity Web (ADW) /=]
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