The Irawaddy Dolphin (Orcaella brevirostris)

Key Facts

A Dolphin And Not A Fish!

Many people confuse dolphins with big fish.  Irrawaddy dolphins are not fish and need to breathe air just like humans and other land animals.  There are a number of differences between dolphins and fish.

Dolphin’s Can Live In Freshwater?

Irrawaddy dolphins are known to inhabit only three rivers in the world – all in Southeast Asia; the Mahakam River of Kalimantan, Indonesia, the Ayeyarawaddy River of Myanmar and the Mekong River of southern Lao, Cambodia and Vietnam.

There are four other species of dolphins in the world which are only found in freshwater habitats.  These are the Ganges, Indus, Amazon and Yantgze River dolphins.  These dolphins are found in the Ganges and Indus rivers of Pakistan, Bangladesh, India and Nepal, the Yantgze River of China and the Amazon River in south America respectively.  All these dolphins live their whole life in the river system.  They do not enter coastal or ocean waters and are not found anywhere else in the world. 

As with the Irrawaddy dolphin, there are four other species where populations can be found in both riverine and estuarine/coastal habitats.  These are the Tucuxi and Franciscana (south America) and Finless porpoise (Asia).

It is very important to protect and conserve these generally small freshwater dolphin populations, as once they are gone, they will be gone forever.

Why Are The Dolphins Here?

Photo: Pete Davidson

It is unknown why some Irrawaddy dolphins inhabit coastal waters, while three populations have entered major river systems ofsoutheast Asia (up to 1000 km from the ocean).

Irrawaddy dolphins were known to previously range widely throughout the Mekong River in the wet season (June to December).  Recent interviews indicate that few dolphins now move downstream of Kratie during the wet-season. 

During the dry season (January to May) the population can be found in the upper reaches of the Cambodian Mekong, from Kampi Pool (Kratie Province) 190 km north to Khone Falls. 

Along this river section, the population is distributed primarily in nine deep water pool areas. 

From January to May, water levels in the Mekong River are at their lowest and the dolphins need to find areas that are deep enough to allow them to swim throughout the dry season. 

These deep water pools are also areas where fish congregate, providing food for the dolphins. 

Dolphins can be sighted every day throughout the year at Kampi Pool.  This pool is one of the larger deep water habitats in the upper reaches of the Mekong River – and the most important for the Irrawaddy dolphins.  The next most important pool for dolphins is Chiteal on the Lao/Cambodian border.

Global Irrawaddy Dolphin Status

Irrawaddy dolphins are found in both coastal and riverine waters from the Bay of Bangal, east to southern Philippines (Palawan) and south to northern Australia.  The status of coastal populations remains largely unknown, but most are thought to be small and localised.

Irrawaddy dolphins inhabiting Australian/Papua New Guinea coastal waters have recently been proposed as a separate species to Irrawaddy dolphins inhabiting Asian coastal/riverine waters.

Due to intense competition with humans for freshwater resources, all riverine populations are small and declining.  Due to recent study, the Mahakam River sub-population was recently listed as ‘Critically Endangered” by the IUCN – with a total population of no more than 50 mature individuals.  Additional proposals to upgrade sub-populations of Irrawaddy dolphins to ‘Critically Endangered’ have been submitted for sub-populations from:  the Mekong River (Vietnam, Cambodia and southern Laos), Ayeyrawady River (Myanmar), Songkhla Lake (Thailand) and Malampaya Sound (Philippines)

Mekong River Irrawaddy Dolphin Population

Although the Irrawaddy dolphin (commonly known as the Mekong River dolphin) has been locally known in the Mekong River for many decades there has been very little previous research on this population.  The first known record in the literature was by an early French explorer, Henri Mouhout, who described them occurring near Phnom Penh.  Studies on the internal anatomy of Irrawaddy dolphins from the Mekong River were conducted in 1973.  Unfortunately, as with much early wildlife research, these studies resulted in the deaths of two animals which were taken from Kampi Pool, Kratie Province by an over-enthusiastic French man.  This French man also sighted dolphins in Tonle Sap – the only known confirmed records from Tonle Sap. 

From the 1970’s to 1990’s, large numbers of dolphins were known to have died through human-induced mortality in the Mekong River.  These threats included direct killing during the Pol Pot regime (1975-1979) in Tonle Sap Great Lake for their oil, being shot for target practice by both Vietnamese and Khmer in the 1980’s and killed accidentally through the use of dynamite fishing.

In the early 1990’s, field research confirmed the presence of Irrawaddy dolphins in southern Lao P.D.R. and to a lesser extent northeast Cambodia.  All studies in southern Lao were conducted at Chiteal Pool (also known as ‘Veun Nyang'), a small deep water pool on the Lao/Cambodian border, which is the northernmost range of Irrawaddy dolphins in the mainstream Mekong River. 

In March 2002, an Irrawaddy dolphin carcass was found in Tien River (a branch of the Mekong River) in An Giang Province, Vietnam (near the Cambodian border).  This is the only recent Irrawaddy dolphin report from the Vietnamese Mekong River – the last known report being in 1973. 

Current information about the Mekong River Irrawaddy dolphin population:

Abundance

• The entire Irrawaddy dolphin population in the Mekong River now numbers no more than 170 individuals.
• Dolphin’s were commonly sighted throughout the Mekong River and associated tributaries in the early 1900’s.  There is no doubt that the population has declined significantly in recent years.

Distribution

• The dolphins distribution in the dry season is thought to be restricted to the upper reaches of the Cambodian Mekong River from Kratie to Khone Falls (5 km north from the Lao/Cambodian border).
• During the wet season, dolphins distribute throughout the Mekong River, south to at least Phnom Penh and probably into Vietnam, and up into major river systems (such as the Sekong and Sesan Rivers). 
• The presence of Khone Falls (5 km north from the Lao/Cambodian border) prevents any further movement north of the population.
• During the early 1970’s, Irrawaddy dolphins were regularly reported in Tonle Sap Great Lake.  It is believed that due to direct hunting in the mid 1970’s and intensive fishing pressure, dolphins are no longer found in significant numbers (if at all) in Tonle Sap Great Lake. 

Important Habitats

• Kampi pool is one of the most important areas for the survival of dolphins in the Mekong River. 
• There are eight other important pools from Kratie to the Lao/Cambodian border, where dolphins reside during the dry season.