By damming the mainstream of the lower Mekong River in Bangkok, Thailand, there is a significant new threat to the survival of the Mekong giant catfish, according to a new study commissioned by WWF.
Being one of the world's largest and rarest freshwater fish, the numbers of catfish are already in steep decline due to habitat destruction, overfishing, and dams along the Mekong's tributaries.
The exact population size of the Mekong giant catfish is unknown, but it is thought that there could be as little as a couple of hundred adult fish left.
The new study shows the status of this elusive species, including data on its numbers, distribution, threats, and measures needed to prevent losing this fish.
Revealing that the Xayaburi dam on the Mekong mainstream in northern Laos would prove an impassable barrier for the giant cat fish, the study proves that the dam risks sending the species into extinction.
The catfish are capable of reaching up to three metres in length and weighing as much as 300kg.
Dr Zeb Hogan, the study's author and associate research professor at the University of Nevada says: "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.
"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."
During the Mekong River commission meeting in 2011, environment and water ministers had agreed to delay a decision on building the Xayaburi dam, pending further studies on environmental impacts. Last November, this agreement was swept aside when Laos decided to forge ahead with construction.
There have been growing concerns centred on the serious gaps in data and failures to fully account for the impacts of this US$3.5-billion project, particularly concerning sediment flow and fisheries.
Pöyry, the Finnish firm advising Laos on the dam construction, argues that 'fish passages' can be built. It claims that this will enable fish to get past the dam's turbines and down the river, but this claim has never been put into practise.
Dr Eric Baran with the World Fish Centre says: "You can't expect fish ladders to work without understanding your target species, their swimming capabilities, and the water current that will attract these fish toward the pass entrance.
"Research is still needed to ensure mitigation efforts will work."
Once being widely distributed through the Mekong river basin, the giant catfish were relatively abundant up until the early 1900s. Since then, the numbers have plummeted. The species is now limited to the Mekong and its tributaries in Cambodia, Laos and Thailand. According to catch figures the numbers have dropped from thousands of fish in the late 1800's to dozens in the 1900's, and only a few in recent times.
Laws have been put into place in Thailand, Laos and Cambodia to regulate fishing for Mekong giant catfish, with a ban on fishing the species in Thailand and Cambodia. However the species is still fished illegally and caught accidentally in fisheries targeting other species.
Dr Lifend Li, Director of WWF's Global Freshwater Programme says: "The Mekong giant catfish symbolises the ecological integrity of the Mekong River because the species is so vulnerable to fishing pressure and changes in the river environment. Its status is an indicator of the health of the entire river, and its recovery is an important part of the sustainable management of the Mekong basin.
"The Mekong giant catfish can be saved, but it will take a level of commitment from all lower Mekong countries, as well as international organizations and donors, that currently does not exist."
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