Is it the end for the Mekong giant catfish?

(Photo: Jean-Francois Helias)

Thursday 12 August 2010
Dr Heok Hee Ng
Practical Fishkeeping (UK)

Proposed dams in the lower Mekong River in the Indochinese peninsula will doom the Mekong giant catfish (Pangasianodon gigas) to extinction, according to the report “River of Giants: Giant Fish of the Mekong” recently released by the World Wildlife Fund.

There are 11 dams proposed in the Mekong River south of China (eight in Laos and three in Cambodia), and the construction of any one of these dams will prevent the catfish from migrating upriver (from the Tonle Sap Lake in Cambodia to northern Thailand and Laos) to spawn.

The catfish, reaching sizes of up to 3m and weights of up to 350 kg, cannot swim across dams because of their sheer bulk, making fish ladders (the traditional solution in allowing migratory fish to pass through artificial barriers such as dams) useless in alleviating this problem.

Populations of the giant Mekong catfish have already plummeted by 90% over two decades, and the dams might prove to be the last straw.

The dams not only spell doom for the Mekong giant catfish, as the Mekong River is also home to four of the world's 10 largest freshwater fish species.

The other three species, also highlighted in the report, are the giant freshwater stingray (Himantura chaophraya) pictured above, the giant dog-eating catfish (Pangasius sanitwongsei), and the giant barb (Catlocarpio siamensis).

According to Dang Thuy Trang, Mekong River Ecoregion Coordinator for the WWF Greater Mekong Programme, "More giant fish live in the Mekong than any other river on Earth… Currently, the Lower Mekong remains free-flowing, which presents a rare opportunity for the conservation of these species. But the clock is ticking."

According to the report, even more is at stake than the fates of the giant fishes of the Mekong River. Construction of the dams are also likely to exacerbate the impacts of climate change on the Mekong River Delta, one of the world’s most fertile regions for agriculture (particularly rice) and one of its most productive for both capture and culture fisheries.

The dams are likely to withhold sediment flowing downstream, reducing the ability of the delta to replenish itself, and rendering it more vulnerable to climate change effects such as increased erosion, saltwater intrusion from sea-level rises, and more intense tropical storms.

This would eventually lead to the displacement of millions of people and the loss of millions' of dollars worth of agricultural land.

Some of these fishes can be seen in a new TV series featuring giant fish.

For more information, see the report: River of Giants: Giant Fish of the Mekong.

Giant Stingray, 350-Kilogram Catfish Threatened by Mekong Hydropower Dams

Jul 27, 2010
By Stuart Biggs
Bloomberg

Dams and infrastructure development along Asia’s Mekong River threaten the survival of some of the world’s largest freshwater fish species, including the giant freshwater stingray and the Mekong giant catfish, WWF said.

Hydropower dams block migration routes to spawning grounds in the Mekong, home to four of the world’s 10 largest freshwater fish species, according to a report published today by WWF, formerly the World Wildlife fund.

Populations of Mekong giant catfish, which can weigh as much as 350 kilograms (772 pounds) and are the world’s third- largest freshwater fish, have declined 90 percent in two decades, the report said. The river is also home to the largest freshwater species, the giant freshwater stingray, which can grow up to 600 kilograms.

China has completed four dams on the upper reaches of the 4,425-kilometer (2,750-mile) Mekong, the world’s 11th-longest river, and four more are planned before 2025 to provide a total capacity of 15,200 megawatts, enough to provide electricity for 75 million people. China’s first upstream dam became operational in 1993, with subsequent openings in 2003 and 2008.

Another 11 mainstream dams are in various stages of development in Laos, Thailand and Cambodia, in addition to smaller dams on the Mekong’s tributaries. More than 60 million people live in the Mekong’s lower basin, an area larger than the U.S. state of Texas.

Mainstream dams constitute “the single largest threat” to the Mekong’s wetlands, home to the world’s largest inland fishery, the Mekong River Commission said in an April 2 report.

Dry weather reduced Mekong water levels to their lowest in three decades earlier this year, raising scrutiny about management of the river as governments aim to harness its potential to provide food and generate electricity.

To contact the reporter on this story: Stuart Biggs in Tokyo at sbiggs3@bloomberg.net.

World's Largest Catfish Species Threatened by Dam

April 8, 2008
Stefan Lovgren at Khone Falls, Cambodia
for National Geographic News

This is the sixth story in a continuing series on the Megafishes Project. Join National Geographic News on the trail with project leader Zeb Hogan as he tracks down the world's largest freshwater fishes.

In the swift currents of the Mekong River in northern Cambodia, fishers expertly navigate their longboats past rock outcroppings and fallen logs.

But soon these wild waters may be tamed. Plans for the construction of a large hydroelectric dam just across the border, at Khone Falls in Laos, would permanently alter one of the most pristine areas in Southeast Asia.

The dam is one of several being planned on the mostly untouched Mekong River, which meanders through six countries—China, Myanmar (Burma), Thailand, Laos, Cambodia, and Vietnam (see map).

The future of the Mekong was a key issue when the prime ministers of those countries met for a regional summit earlier this week in the Laotian capital of Vientiane.

The Don Sahong dam at Khone Falls, one of five dams that Laos is planning along the Mekong, will block the deepest channel on the section of the river that migratory fish pass through when the water level is at its lowest, conservationists say.

One of those migratory fish is the critically endangered Mekong giant catfish, which holds the record as the largest freshwater fish ever caught. The record catch, made in northern Thailand in 2005, tipped the scales at 646 pounds (293 kilograms).

"An impassable dam at the falls could cause the extinction of the Mekong giant catfish species," said Zeb Hogan, a fisheries biologist at the University of Nevada in Reno.

Hogan, who visited the Khone Falls area last week, heads the Megafishes Project, a three-year effort to document the 20-plus species of freshwater fish that measure at least 6.5 feet (2 meters) in length or 220 pounds (100 kilograms) in weight.

(The Megafishes Project is partly funded by the National Geographic Society, which operates National Geographic News.)

Spawning Ground

Fishers at Khone Falls had long known that the giant catfish traveled through their area.

But in 2007 Thai photographer Suthep Kritsanavarin for the first time photographed a giant catfish caught at Khone Falls.

Giant catfish were once plentiful throughout the Mekong River basin, but in the last century the population has declined 95 to 99 percent, according to Hogan.

The massive fish is not targeted by fishers, but it is sometimes caught as bycatch. In Cambodia, where the largest population of giant catfish is found, eight of the giant fish were caught last year.

Although fishing is the biggest immediate threat to the giant catfish in the Mekong, dams and habitat fragmentation could disrupt the animal's ability to reproduce, Hogan said.

"There is only one known spawning ground for Mekong giant catfish, and that spawning ground is in northern Thailand," he said.

"Until we know better, we have to assume that fish from Cambodia may migrate to Thailand to spawn."

The construction of the Don Sahong dam, which is slated for completion in 2010, would make that migration impossible, Hogan said.

Untouched

Advocates of the dams point to the enormous hydropower potential that the Mekong offers to an energy-hungry region. With oil prices at record levels, the projects have taken on added urgency, they say.

So far the Mekong runs almost uninterrupted; only China has dammed the river at two locations in Yunnan Province.

One of the dams that China is now building will be second in size only to the Yangtze River's Three Gorges Dam.

"China, as an upstream country, will never do anything that will harm the interests of downstream countries," He Yafei, China's assistant foreign minister, told reporters before last week's regional summit.

But officials in Vietnam, where the Mekong empties into the South China Sea, say water extraction for farm irrigation upstream has already caused ocean salt water to move inland, destroying rice fields.

Conservationists likewise warn that the new dams could harm fish stocks that millions of people throughout the Mekong depend on.

"Fisheries resources are essential to the population of the Mekong Basin," said Eric Baran of the nonprofit World Fish Center in Phnom Penh, Cambodia.

"In Cambodia, for instance, the fish catch contributes 65 to 75 percent of the animal protein of households."

More than a thousand fish species live in the Mekong River system, a biodiversity second only to the Amazon in South America, Baran said.

In a report last year, the World Fish Center warned that the economic benefits of the U.S. $300-million Don Sahong dam may be outweighed by losses from local fisheries, whose production has been estimated at over U.S. $2 billion a year.

Deep Channel

At Khone Falls the Mekong River drops up to 100 feet (30 meters) from the Khorat plateau to the Mekong plain, forming a complex network of narrow channels, called hoo in Lao.

Scientists have found that the area supports at least 201 fish species, including several endemic or endangered species.

The area is also home to one of the few remaining concentrations of freshwater dolphins in the Mekong.

The dam will block Hoo Sahong, the deepest channel and the only one that migratory fish can pass through at the peak of the dry season, in April and May, when the Mekong is at its lowest.

Nongovernmental organizations in Cambodia called on their government this month to ask Laos for a construction moratorium on the Don Sahong dam to allow for more environmental assessments.

Hogan admits that dams provide a number of benefits, including flood control, water for irrigation, and electricity.

"But it is also important to consider the costs," he said, "especially in an area where a large part of the population is dependent on fish for food."

"From a migratory fish's perspective, there is nothing worse than a dam."