Big Trouble for Asia's Giant Catfish

John Roach
for National Geographic News
May 15, 2003
This time of year, fishers along the banks of the Mekong River in the
village of Chiang Khong in northern Thailand wait expectant, as they
have for hundreds of years, for the arrival and harvest of giant
catfish. But this year the catfish may never come.

"No fish have been captured in Thailand since 2001 and the giant catfish is in danger of disappearing from Thailand completely," said Zeb Hogan, a fisheries biologist at the University of California at Davis.

Hogan leads the Mekong Fish Conservation Project, an effort to protect vulnerable populations of migratory fish in the Mekong River Basin, including the critically endangered Mekong giant catfish (Pangasianodon gigas). The catfish is one of several fish species presently endangered in the watershed.

The project is supported by the National Geographic Society's Conservation Trust, the Cambodian Department of Fisheries, and the conservation group Save Cambodia's Wildlife.

Fish Threats

Called Pla Buek in Thai, the giant catfish can weigh as much as 650 pounds (300 kilograms) and measure up to 10 feet (3 meters) in length. They are the largest scaleless freshwater fish in the world.

Chainarong Sretthachau, director of the conservation group Southeast Asia Rivers Network in Chiang Mai, Thailand, said threats to the giant catfish include commercial fishing, their touting to tourists as a food said to impart wisdom, and dynamite blasting of their spawning ground.

"The rapids and whirlpool ecosystem in Chiang Khong-Chiang Saen is the only area in the Mekong that giant catfish use as a spawning ground and it will be destroyed by Mekong rapids blasting," said Sretthachau.

The blasting project is part of navigation channel improvements planned by the governments of China, Burma, Thailand, and Lao People's Democratic Republic. According to Sretthachau, the spawning ground rapids will be dynamited in December.

As part of their project, Hogan and his colleague Heng Kong, a researcher with Cambodia's Department of Fisheries, buy live fish from fishers in Cambodia. They weigh and measure the fish, gather DNA samples for genetic studies, tag endangered fish, and release them back into the wild.

Over the short-term, the project keeps a handful of endangered fish, including the giant catfish, alive as researchers gain insight into fish migration patterns, habitat use, and mortality rates.

"In the longer term, we hope our migration studies and environmental awareness campaign will lead toward more sustainable management of Cambodia's fisheries," said Hogan.

Buy and Release

Hogan launched the conservation project in Chiang Khong, Thailand, in 2000 but moved it to Cambodia in 2001 due to the collapse of Thailand's giant catfish fishery. "Cambodia is now the last place in the world where the giant catfish is captured on a regular basis," he said.

But Cambodia's giant catfish numbers are also low. Fishers along the Tonle Sap River, a tributary to the Mekong, set bag nets from October to December. In 2000, fishers hauled out 11 giant catfish. In 2001 they caught seven. In 2002 they caught just five.

Hogan and Kong have hooked fishers on their conservation project. Whenever fishers catch an endangered fish they call the biologists, no matter what time of day.

The researchers rush to the river and pay the fisherman market price for the catch then measure, weigh, and release the fish downstream from the fishnets.

"We pay for the fish as an incentive for fishermen to report their catches and to keep rare species alive and in the river instead of dead on a dinner plate," said Hogan. Fishermen are also paid a little over U.S. $1 to return tags from recaptured fish.

Hogan says the money is not enough to give the fishers an added incentive to go after the endangered fish and thus does not influence their fishing behavior.

Mekong Migration

The researchers have tagged nearly 2,000 fish, most of them river catfish (Pangasianodon hypophthalmus). The fish are tagged in the Tonle Sap Lake and Tonle Sap River from October to December as they begin their winter migration.

Reports of the re-captured fish will allow the researchers to establish growth rates by comparing the weight and length of the fish from when they were first tagged to when they were captured. The re-captured fish also allow the scientists to track the fishes' spawning migration up the Mekong River.

"The migration study has conservation relevance because it demonstrates the importance of free-flowing rivers and the link between floodplain habitat like the Tonle Sap Lake and the spawning habitat of the Mekong River," said Hogan.

The researchers ultimately hope that several no fishing zones will be established in the region and that the Tonle Sap Lake, Tonle Sap River, and Mekong River will be recognized as critical habitat for migratory fish.

Conservation Status

Currently, the Mekong giant catfish P. gigas is listed as endangered by the World Conservation Union (IUCN) and is in the process of being re-designated as critically endangered.

While the Mekong river catfish (P. hypophthalmus) is not recognized as endangered, Hogan said observational data suggests that its populations are declining rapidly, with catches down 90 percent from 20 years ago.

The range of the giant carp (Catlocarpio siamensis) has also declined and is a focus of Hogan's conservation research.

Sretthachau said fishing is a way of life for the people of the Mekong River Basin and the loss of these species "means millions of people will lose their food security, livelihoods, and economic system."

Hogan and his colleagues seek to raise conservation awareness through their forthcoming book The Long Journey of the Giant Catfish. Once published, the book will be distributed to Cambodian school children.

"Since the Mekong giant catfish is migratory, the protection of the Mekong giant catfish may benefit many other species that use identical habitat," said Hogan.

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