Friday, June 21, 2013

[Conservation • 2013] A Mekong Giant - Current Status, Threats And Preliminary Conservation Measures For The Critically Endangered Mekong Giant Catfish Pangasianodon gigas (Chevey 1930)

A Mekong Giant - Current Status, Threats And Preliminary Conservation
Measures For The Critically Endangered Mekong Giant Catfish

Dams could signal death knell for Mekong giant catfish 

– Damming the mainstream of the lower Mekong River would represent a significant new threat to the survival of the Mekong giant catfish, one of the world’s largest and rarest freshwater fish, according to a new study commissioned by WWF. 

The study sheds new light on the status of this elusive species, including data on its numbers, distribution, threats and measures needed to prevent its disappearance. While the exact population size is unknown, there could be as few as a couple of hundred adult Mekong giant catfish fish left.

According to the study, the Xayaburi dam on the Mekong mainstem in northern Laos would prove an impassable barrier for the migratory giant catfish – which are capable of reaching up to three metres in length and weighing as much as 300kg – and risks sending the species to extinction.

“A fish the size of a Mekong giant catfish simply will not be able to swim across a large barrier like a dam to reach its spawning grounds upstream,” said the study’s author and associate research professor at the University of Nevada, Dr. Zeb Hogan. 

“These river titans need large, uninterrupted stretches of water to migrate, and specific water quality and flow conditions to move through their lifecycles of spawning, eating and breeding.” 


photo: Zeb Hogan 

Executive Summary 
Conservation Status: The Mekong giant catfish, Pangasianodon gigas (Chevey 1930), is one of the most endangered fish in Southeast Asia. It is listed on the IUCN Red List of Threatened Species as Critically Endangered A4abcd (IUCN 2011). The Mekong giant catfish is listed on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and Appendix I of the Convention on Migratory Species (CMS).

Distribution: P. gigas is a Mekong endemic. Historically, Mekong giant catfish occurred throughout the large rivers of the Mekong River Basin in Vietnam, Cambodia, Lao PDR, Thailand, and possibly Burma and southwestern China (Smith 1945, Lenormand 1996, Roberts and Vidthayanon 1991). There is some evidence that Mekong giant catfish were very widely distributed and relatively abundant in the 1800’s and early 1900’s. Mekong giant catfish now appear limited to the Mekong and its tributaries in Cambodia, Lao PDR, and Thailand. The species has also been introduced into reservoirs and rivers in Thailand but these introductions have failed to result in self-sustaining populations (Hogan et al. 2001). 

Population size: Evidence suggests that populations of Mekong giant catfish have been declining throughout the basin for the last several decades (Pavie 1904, Giles 1935, Smith 1945, Hogan et al. 2001, Hartmann et al. 2008). P.gigas is now very rare throughout its range and no significant catch has been reported from northeast Thailand, southern Lao PDR, or Vietnam since 1980. In northern Thailand, the catch of Mekong giant catfish has been declining steadily for the past 20 years (Hogan 1998). Basinwide catch numbers are difficult to ascertain but appear to have dropped from thousands of fish in the late 1880’s (Pavie 1904), to hundreds of fish in the 1920’s and 1930’s (Giles 1935), to dozens of fish in the 1990’s (Hogan et al. 2004), to less than 10 fish in recent times (Stone 2007).

Habitat and ecology: The ecology of the Mekong giant catfish is poorly understood. Most available information comes from catch records which indicate that Mekong giant catfish use a broad range of habitats throughout their life cycle. Juvenile fish have been reported from the Mun and Songkhram Rivers in Thailand and the Tonle Sap Lake in Cambodia. Adult fish are believed to inhabit deep water areas of the Mekong River especially during the dry season (Mattson et al. 2002). P. gigas is migratory, but the extent of migrations is unknown. Migrating adults have been recorded moving out of the flooded habitats of Tonle Sap Lake and into the Mekong at the end of the rainy season (October-December), moving over the Khone Falls in July and August (Mollot unpublished data), and making spawning migrations in northern Thailand and Lao PDR in late May and early June (Hogan et al. 2004). Genetic data indicate that all P. gigas in the basin may be part of one, panmictic population (Ngamsiri et al. 2007). 

A Mekong Giant - Current Status, Threats And Preliminary Conservation 
Measures For The Critically Endangered Mekong Giant Catfish

Dams could signal death knell for Mekong giant catfish