The Irrawaddy dolphin (Orcaella brevirostris) is a type of dolphin that can live in both saltwater and freshwater. It is found in small groups near coastlines, in rivers, and in areas where saltwater and freshwater mix, such as parts of the Bay of Bengal and Southeast Asia. This dolphin looks very similar to the Australian snubfin dolphin, which belongs to the same family, Orcaella. The Australian snubfin dolphin was not recognized as a separate species until 2005. The Irrawaddy dolphin has a dark blue to dark gray color. While it lives in many rivers and coastal areas across South and Southeast Asia, the largest groups of these dolphins are found in Chilika Lake in Odisha, India, and Songkhla Lake in southern Thailand.

Taxonomy

The first known description of the Irrawaddy dolphin was written by Sir Richard Owen in 1866. He based his description on a sample found in 1852 in the harbor of Visakhapatnam on India’s east coast. This dolphin is one of two species in its genus. In the past, it was sometimes placed in a family that included only itself, or grouped with the families Monodontidae and Delphinidae. Most scientists now agree that it belongs to the Delphinidae family.

Description

The Irrawaddy dolphin has a grey to dark slate blue color, with a lighter color on its underside. It does not have a unique pattern. Its back fin is small and rounded, located near the middle of its back. The dolphin has a high, rounded forehead and no beak. The front of its snout is blunt. Its flippers are wide and rounded. The finless porpoise (Neophocaena phocaenoides) looks similar but lacks a back fin. The humpback dolphin (Sousa chinensis) is larger, has a longer beak, and a bigger back fin. The Irrawaddy dolphin weighs between 90 to 200 kg (200 to 440 lb) and grows to 2.3 m (7.5 ft) in length when fully grown. The longest recorded length is 2.75 m (9.0 ft), measured in a male in Thailand.

The Irrawaddy dolphin resembles the beluga in appearance but is most closely related to the killer whale. It has a large, rounded head and a blunt snout. Its beak is not clearly defined. The back fin is located about two-thirds of the way along its back. This fin is short, blunt, and triangular. The shape of the back fin varies between individuals. The flippers are long and wide. These dolphins are usually two-toned, with the back and sides being grey to bluish-grey and the belly lighter in color. Unlike other dolphins, the Irrawaddy dolphin has a U-shaped blowhole on the left side of its head, which opens toward the front. Its short snout looks different from other dolphins, and its mouth has 12 to 19 small, peg-like teeth on each side of the jaw.

Behaviour

Irrawaddy dolphins use clicks, creaks, and buzzes to communicate. These sounds are most common at a frequency of about 60 kilohertz, which they may use to find food. They eat bony fish (like catfish), fish eggs, squid, octopus, cuttlefish, and crustaceans. Observations of dolphins in captivity show they may suck food into their mouths. Irrawaddy dolphins can spray water up to 1.5 meters (about 5 feet) to help catch fish. This behavior is used to herd fish into a group or to remove water swallowed during feeding. Some dolphins in captivity have been trained to perform this action on command. These dolphins swim slowly but can reach speeds of 20–25 kilometers per hour (about 12–16 miles per hour) when chased by boats. In one year, female dolphins may travel up to 45 kilometers (about 28 miles), and males may swim up to 100 kilometers (about 62 miles).

Irrawaddy dolphins are often shy around boats and do not commonly ride on their bows. They usually dive when frightened. They move slowly but may spyhop (rise to the surface to look around), roll, or breach (jump out of the water). They are often found in groups of 2–3 dolphins, though sometimes up to 25 may gather. Smaller groups of fewer than six dolphins are most common. Traveling in groups helps them hunt, build social connections, and mate. In Brunei Bay, some dolphins are near the mouths of the Temburong and Aloh Besar rivers. These dolphins are calm and gather around fishing boats during the fishing season, which runs from December to February.

When diving, Irrawaddy dolphins surface by rolling and lift their tail fluke (the flat part of the tail) only for deep dives. Deep dives can last from 30 seconds to 12 minutes. In Laos, 277 group dives were timed, with an average of about 115 seconds (about 1 minute and 55 seconds), ranging from 19 seconds to 7 minutes and 11 seconds.

When Irrawaddy dolphins are forced into areas where other dolphins live, competition may occur. In captivity, humpback dolphins (Sousa chinensis) have been seen chasing and keeping Irrawaddy dolphins in small areas of the tank. In Chilika Lake, local fishers report that Irrawaddy dolphins flee when they meet bottlenose dolphins in the outer channel.

When a male or female dolphin wants to mate, they may chase a partner for a few minutes. They face each other belly to belly and mate for about 40 seconds. After mating, they separate and swim in different directions.

Irrawaddy dolphins reach sexual maturity at 7–9 years. In the Northern Hemisphere, mating occurs from December to June. Their pregnancy lasts 14 months, and females give birth to one calf every 2–3 years. Calves are about 1 meter (3.3 feet) long and weigh about 10 kilograms (22 pounds) at birth. They stop nursing after two years. These dolphins may live up to 30 years.

Irrawaddy dolphins eat fish, crustaceans, and cephalopods. During hunting, groups of about 7 dolphins may circle prey underwater to trap it. These hunting actions happen just below the water’s surface.

Distribution and habitat

The Irrawaddy dolphin is a type of oceanic dolphin that lives in brackish water near coasts, river mouths, and estuaries. It has groups living in freshwater rivers, such as the Ganges, the Mekong, and the Ayeyarwady River, which is where the dolphin gets its name. Its habitat ranges from the Bay of Bengal to New Guinea and the Philippines, but it does not swim far out to sea. It is often seen in the estuaries and bays of Borneo, with sightings from Sandakan in Sabah to areas in Brunei and Sarawak. One individual was found in the Mahakam River in East Kalimantan. Reports of the dolphin in Chinese, Taiwanese, and Hong Kong waters are not reliable.

• Bangladesh: About 3,500 live in the coastal waters of the Bay of Bengal, and 451 (VU) live in the brackish Sundarbans mangrove forest.
• India: 156 live in the brackish-water Chilika Lake in Odisha, as of 2021.
• Cambodia: About 105 live in a 190-km (118-mi) freshwater section of the Mekong River, as of 2024.
• Indonesia: About 70 live in a 420-km (260-mi) freshwater section of the Mahakam River.
• Philippines: About 35 live in the brackish inner Malampaya Sound in Palawan. At least 20 live in Quezon in southern Palawan, and 30–40 live in areas such as Pulupandan, Bago, Negros Occidental, Guimaras, and Iloilo in the Western Visayas Region and Negros Island Region. At least two live in San Miguel Bay in Bicol, which is the easternmost group and the only one in the Pacific Ocean.
• Myanmar: About 58–72 live in a 370-km (230-mi) freshwater section of the Ayeyarwady River.
• Thailand: Fewer than 50 live in the brackish Songkhla Lake, possibly only 14.

The Irrawaddy dolphin has been extinct in Laos since 2022.

Interaction with humans

Irrawaddy dolphins work together with traditional fishers in a helpful way to catch fish. In India, fishers used to tap a wooden key called a lahai kway against the sides of their boats to signal the dolphins to help drive fish into their nets. In Burma, near the upper part of the Ayeyarwady River, Irrawaddy dolphins respond to sounds made by fishers by herding fish toward them using cast nets. Fishers use different methods to get the dolphins' attention, such as tapping a cone-shaped wooden stick on their canoes, hitting their paddles against the water, shaking their nets, or making turkey-like calls. A group of dolphins that agrees to help will form a semicircle around a school of fish, leading them toward the boat. In return, the fishers give the dolphins some of the fish that are caught accidentally. In the past, fishers in the Irrawaddy River claimed certain dolphins were connected to specific fishing villages and helped them catch fish. A report from 1879 showed that fishers often took legal action in native courts to claim fish that their dolphins had helped catch from rival fishers.

People in Laos and Cambodia believe that Irrawaddy dolphins are the spirits of their ancestors. Some say the dolphins have saved people who were drowning and protected them from crocodile attacks. These beliefs and experiences have helped people in Laos and Cambodia live peacefully together for many years. In West Kalimantan, there is a story that the dolphins were once mischievous children who ate rice meant for a shaman. Their mouths burned from the hot rice, so they jumped into the water to cool down and later became dolphins.

Buddhist Khmer and Vietnamese fishers consider the Orcaella dolphin a sacred animal. If they catch a dolphin in their nets, they release it back into the water. However, Muslim Khmer fishers sometimes kill the dolphins for food. This has caused the dolphins to avoid areas near Muslim Khmer communities, as they seem to recognize the local languages and stay away from places where they might be harmed.

Threats

Irrawaddy dolphins are more likely to be affected by human activities than other dolphins that live farther out in the ocean. Drowning in gillnets is the main threat to them across their entire range. Between 1995 and 2001, 38 dolphin deaths were reported, and 74% of these were caused by getting caught in gillnets with large mesh sizes. Most dolphin deaths in all subpopulations are due to accidental capture and drowning in gillnets, dragnets, and bottom-set crab nets in the Philippines. In Burma, electrofishing, gold mining, and dam building are also serious and ongoing threats. Although most fishers care about the dolphins, giving up their traditional way of life is difficult for them.

Another threat to Irrawaddy dolphins is noise pollution from high-speed vessels. This caused the dolphins to dive much longer than usual. The dolphins always changed direction when they saw these large vessels.

In recent years, people in Laos and Cambodia have started using explosives for fishing. The government of Laos has banned this practice, but Cambodia has not made many rules against it. Explosives are sold in local markets, and fishing with nets has been stopped. Using explosives has become popular, but it has caused fish populations, including dolphins, to decline. In Laos, even though explosives are not used, nylon gillnets are still a major threat. Some dolphins get caught in these nets. Poor fishermen often refuse to destroy their nets because it would cost them too much money.

A dam is planned across the Mekong River in Laos. This could harm the endangered Irrawaddy dolphins living downstream in Cambodia. The dam will be built upstream of the dolphins’ main habitat, which could lead to their extinction in the Mekong River. Builders plan to use explosives to dig through rock, creating loud sounds that could harm the dolphins because of their sensitive hearing.

In several Asian countries, Irrawaddy dolphins have been captured and trained to perform in public aquariums. Their unique appearance and behaviors, such as spitting water, spyhopping, and fluke-slapping, make them popular in shows. These dolphins are valuable for aquariums because they can live in freshwater tanks, avoiding the high costs of marine systems. As areas near the dolphins’ habitat have grown economically, more theme parks, casinos, and entertainment venues with dolphin shows have opened.

In 2002, there were more than 80 dolphinariums in at least nine Asian countries.

Collateral deaths of dolphins from blast fishing were common in Vietnam and Thailand in the past. The most direct threat was killing dolphins for their oil.

The IUCN lists five of the seven subpopulations of Irrawaddy dolphins as endangered, mainly due to drowning in fishing nets. For example, the Malampaya population, first discovered in 1986, had 77 dolphins. By 2007, this number dropped to 47, and by 2013, it was 35. In the Mahakam River in Borneo, 73% of dolphin deaths are linked to getting caught in gillnets because of heavy fishing and boat traffic.

Irrawaddy dolphins in Asia are increasingly affected by tourism, such as large numbers of boats traveling through their habitats. The growth of boat tours has placed significant stress on the dolphins.

Cutaneous nodules have been found in several vulnerable Irrawaddy dolphin populations. A more precise estimate shows six populations are affected. The exact outcome of this disease is unknown, but the species is at risk.

Conservation

The Irrawaddy dolphin lives near areas where people live, which makes protecting them harder. The main dangers to these dolphins are getting caught in fishing nets and losing their homes due to environmental damage. People around the world and in different countries are working to help protect them.

The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) helps stop the trade of Irrawaddy dolphins. However, each country is responsible for making sure these rules are followed. Some trade of dolphins for aquariums may have happened, but it has not been a big problem for the species.

Some groups of Irrawaddy dolphins are classified as critically endangered by the International Union for Conservation of Nature (IUCN). These include dolphins in Cambodia, Vietnam (in the Mekong River), Indonesia (in the Mahakam River on Borneo), Myanmar (in the Ayeyarwady/Irrawaddy River), the Philippines (in Malampaya Sound), and Thailand (in Songkhla Lake). Overall, the species is listed as endangered, which means they are at risk everywhere they live. In 2004, CITES moved the Irrawaddy dolphin to Appendix I, which bans all trade of species that are close to extinction.

A plan by the United Nations Environment Programme and the Convention on Migratory Species (CMS) says that protected areas in freshwater rivers can help save Irrawaddy dolphins. These areas work well because dolphins tend to stay in small, specific places. The plan includes ways to reduce the accidental catching of dolphins in fishing nets.

The Irrawaddy dolphin is listed on both Appendix I and Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). Appendix I includes species that are in danger of disappearing, and CMS members must protect them. Appendix II includes species that need help from international cooperation.

The species is also protected by the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (MoU).

In Bangladesh, parts of the Sundarbans mangrove forest where Irrawaddy dolphins live are protected in three wildlife sanctuaries. These areas are part of the Sunderbans World Heritage Site. The Wildlife Conservation Society works with the government to create protected areas for the 6,000 dolphins that remain there.

In Cambodia, Irrawaddy dolphins are fully protected by law. In 2005, the World Wide Fund for Nature (WWF) started a project to help protect the dolphins, with support from the government and local people. In 2012, the Cambodian government created a 180-kilometer stretch of the Mekong River where fishing with certain methods is not allowed. This area is patrolled by river guards to protect the dolphins. In 2006, 12 dolphins were found dead, which led to the hiring of 66 guards along the river to help protect them.

In India, the Irrawaddy dolphin (also called the snubfin dolphin) is protected under the Indian Wildlife Protection Act, which bans killing, moving, or selling them. A project in 2000 helped restore the Chilika Lake by opening a new connection to the Bay of Bengal, which improved the lake's environment and increased the number of dolphins due to more food sources.

In Indonesia, a program called the Conservation Foundation for the Protection of Rare Aquatic Species of Indonesia focuses on protecting the Irrawaddy dolphin in the Mahakam River. The program educates people, monitors the dolphins, and sets up patrols in villages to help protect them.

In Laos, Irrawaddy dolphins have been extinct since 2022. In the 1970s, many dolphins were killed for their oil, and later, fishing with explosives and gillnets caused their numbers to drop. A project by Canadian conservationist Ian Baird helped protect dolphins in the Mekong River and later expanded to Cambodia. Another project, the Si Phan Don Wetlands Project, encouraged communities to create conservation zones and set rules for fishing. Despite these efforts, the last Irrawaddy dolphin in Laos was found dead in 2022.

In Myanmar, the Department of Fisheries created a protected area in a 74-kilometer section of the Ayeyarwady River. Rules in this area include releasing dolphins caught in nets, banning the killing or trading of dolphins, and stopping harmful fishing practices. Mercury poisoning and habitat loss from gold mining have been reduced.

In the Philippines, Malampaya Sound was declared a protected area in 2000. A project by the WWF helped local communities create fishing rules to reduce threats to dolphins. Gear modifications were tested to help protect them. In 2006, a new group of dolphins was found on Guimaras Island.