Irrawaddy Dolphin Orcaella brevirostris

Irrawaddy Dolphin Orcaella brevirostris

IUCN Red List: Endangered

Extant (resident): Southeast Asia: Myanmar, Cambodia, Laos, Thailand, Indonesia, India, Philippines

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Intelligent and social Irrawaddy dolphins, also known as the Mahakam River dolphins or Ayeyarwady river #dolphins have endearing faces. Only 90 to 300 are estimated to be left living in the wild. Their rounded and expressive looking noses liken them to a baby beluga whale or the Snubfin dolphin of Australia. These shy #cetaceans are found in coastal and freshwater habitats across #SoutheastAsia, they live in small groups. Tragically, Irrawaddy dolphins face many human threats, from entanglement in fishing gear to dam construction. Palm oil deforestation, and #pesticide run-off in rivers is another major threat to their survival.

Protecting the Irrawaddy dolphin is paramount. As a keystone species, they maintain biodiversity in their fragile home. These beautiful animals are classified as endangered on IUCN Red list but are critically endangered in some ecosystems. Fight for their survival when you boycott palm oil and go vegan. Support the Boycott4Wildlife movement by using the hashtags #BoycottPalmOil and #Boycott4Wildlife on social media!

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Appearance & Behaviour

Irrawaddy dolphins have a distinctive appearance with their rounded heads, expressive faces, and lack of a beak. With grey to slate blue bellies, they sport small dorsal fins and broad flippers. Socially, they are found in groups of 2-6, although larger gatherings of up to 25 individuals can be found in deeper waters.

Capable spitting streams of water up to 1.5 metres into the air, they also have a U-shaped blowhole, which opens towards the front of their head. Their ability spit water is believed to be used to confuse fish during hunting. These dolphins use suction feeding, drawing prey into their mouths using negative pressure.

Irrawaddy dolphins are slow swimmers, often surfacing in a rolling motion. They can be shy around boats and typically dive when alarmed. They are also known for play behaviours like spyhopping, the practice of holding their bodies out of the water. Also they commonly tail slap and roll on their sides while waving their flippers.

Threats

Palm oil deforestation and pollution:

Pollution run-off from palm oil plantations puts toxic pesticides into their freshwater habitats. These pollutants can lead to serious health issues for the dolphins, such as skin lesions and reduced reproductive success. Deforestation from palm oil production destroys delicate mangroves and estuaries, forcing Irrawaddy dolphins into fragmented ranges, where they struggle to survive.

Industrial fishing bycatch:

The greatest threat to Irrawaddy dolphins is accidental entanglement in fishing gear, particularly gillnets. Dolphins trapped in these nets often drown before they can be rescued. In areas such as the Mekong River, gillnet bycatch accounts for a significant number of dolphin deaths. In some regions, fishing practices involving explosives or electrofishing further contribute to the decline of dolphin populations.

Habitat loss due to dam construction

The construction of dams on major rivers, such as the Mekong and Ayeyarwady, disrupts the natural flow of water. This impacts fish migration and isolates dolphin populations. These dams also prevent the dolphins from accessing essential deep-water pools, which are vital for their survival. Noise pollution from dam construction generates noise pollution and shock waves. This damage the dolphins’ sensitive hearing structures, leading to injury or death.

Industrial river waste and pesticide run-off:

Irrawaddy dolphins’ habitats are increasingly contaminated by pollutants such as pesticides, industrial waste, and oil. Runoff from agricultural activities, including palm oil plantations, introduces toxic substances into the rivers and estuaries where these dolphins live. Additionally, sedimentation caused by deforestation and poor land practices reduces water depth, altering the ecosystems on which the dolphins rely.

Boat traffic interfering with their echolocation

The growth of unregulated tourism in dolphin habitats has led to increased boat traffic. A major cause of fatal collisions with dolphins. Noise pollution from boats also interferes with the dolphins’ echolocation abilities. This makes it hard for them to find and catch prey.

Habitat

Irrawaddy dolphins are found in coastal and freshwater riverine habitats across Southeast Asia. Coastal areas include the Bay of Bengal, and river systems such as the Mekong, Mahakam, Ayeyarwady, and Ganges Rivers. They prefer shallow, brackish waters such as river mouths, estuaries, and mangrove channels. Freshwater populations are found in the Ayeyarwady, Mahakam, and Mekong Rivers, among others. These dolphins are highly dependent on the health of these ecosystems, which are increasingly under threat from human activities.

Diet

Irrawaddy dolphins are opportunistic feeders, consuming a variety of fish, crustaceans, and cephalopods. They are known to follow the tides. Moving inshore with high tides and further offshore as the tides go out, likely tracking their prey. In freshwater habitats, these dolphins sometimes surface with mud on their heads or backs, indicating they feed on bottom-dwelling species.

Mating and breeding

Irrawaddy dolphins reach sexual maturity between seven to nine years of age. Mating usually occurs between December and June in the Northern Hemisphere, with a gestation period of approximately 14 months. Females typically give birth to a single calf every two to three years, and calves are weaned after two years. Their lifespan is about 30 years, though this can vary depending on environmental conditions and threats faced by different subpopulations.

Support Orcaella brevirostris by going vegan and boycotting palm oil in the supermarket, it’s the #Boycott4Wildlife

Several organisations are working to protect the Irrawaddy dolphin and their habitats. The Irrawaddy Dolphin Conservation Project in Myanmar focuses on protecting the dolphins in the Ayeyarwady River through anti-poaching measures, habitat restoration, and education. The Wildlife Conservation Society of Bangladesh work to create protected areas in the Sundarbans mangrove forest to safeguard dolphin populations. Indonesia’s Mahakam River population is monitored by local NGOs working to reduce bycatch and raise awareness.

Further Information

Minton, G., Smith, B.D., Braulik, G.T., Kreb, D., Sutaria, D. & Reeves, R. 2017. Orcaella brevirostris (errata version published in 2018). The IUCN Red List of Threatened Species 2017: e.T15419A123790805. https://dx.doi.org/10.2305/IUCN.UK.2017-3.RLTS.T15419A50367860.en. Accessed on 18 March 2025.

Wikipedia contributors. (2024). Irrawaddy dolphin. In Wikipedia, The Free Encyclopedia. Retrieved from https://en.wikipedia.org/wiki/Irrawaddy_dolphin

Whale and Dolphin Conservation. (2024). Irrawaddy dolphin. Retrieved from https://au.whales.org/whales-dolphins/species-guide/irrawaddy-dolphin/

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