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Asia

The teeming Mekong

The Mekong River is one of the biggest freshwater fisheries in the world, but conservationists fear that dams planned for the river could prove disastrous for many species that live there, and the people who rely on them for food.

/ 14 PHOTOS

Fishing boats ply the Tonle Sap River in Cambodia, catching migratory fish as they move from the large inland lake to the Mekong River at the end of the rainy season.

Dr. Zeb Hogan / University of Nevada, Reno
Khmer man with a Mekong giant catfish, Pangasianodon gigas, on the Tonle Sap River, Cambodia on October 21, 2002.  This fish weighed approximately 160kg and measured about 250cm in length.  In recent times, the maximum size of Mekong giant catfish is 300cm and 300kg.  The World Conservation Union - IUCN reclassified the Mekong giant catfish as critically endangered in 2003.  Popualtions have declined by about 90% over the past 20 years.  Mekong giant catfish migrate out of the Tonle Sap Lake and into the Mekong River at the end of the rainy season.

Among the fish populations that could be harmed by the Xayaburi dam in Laos is the critically endangered Mekong giant catfish, considered by the Guinness Book of World Records to be the world’s largest freshwater fish. The fish, which grows to 650 pounds and about 10 feet long, is only found in the Mekong River. It is migratory, moving between downstream habitats in Cambodia upstream to northern Thailand and Laos each year to spawn. Some experts fear the Xayaburi dam could block the migration and drive the giant catfish to extinction.

Zeb Hogan

Fish and fishing have been a central part of life along the Mekong for thousands of years. This ancient carving from Angkor Wat illustrates the importance of fish in everyday life and shows some of the same carp and catfish species that are staples today.

Dr. Zeb Hogan / University of Nevada, Reno

Fishermen unload their catch during the peak migration of fish in the Tonle Sap River in Cambodia. During these periods, fishermen catch thousands of tons of fish and fish that they barter for other essential goods, like salt. Migratory fish – and the people that depend on them -- are the most vulnerable to the effects of dams.

Dr. Zeb Hogan / University of Nevada, Reno

Migratory fish, like these small carp from Cambodia known as "trey riel” or money fish, make up an estimated 40 percent to 70 percent of the 2.5 million metric tons of fish harvested from the Mekong River basin each year.

Dr. Zeb Hogan / University of Nevada, Reno

The Tonle Sap Lake, is the largest inland lake in Southeast Asia. In the dry season, the shallow lake spreads over 2,500 square kilometers; at the height of the rainy season its surface area expands fourfold and the maximum depth increases from 4 meters to 10 meters. Life around the lake, including local people, is uniquely adapted to the seasonal cycles. During the dry season, huge numbers of fish migrate out of the Tonle Sap Lake to the Mekong River. Local people take advantage this annual movement by living in floating villages, as seen in the photo, and fixing all manner of traps and nets to snare the migrating fish – such as these huge “arrow” traps, which can be over a mile long.

Dr. Zeb Hogan / University of Nevada, Reno

The endangered giant barb, Catlocarpio siamensis, is the largest cyprinid (carp) in the world, growing to an estimated 600 pounds. The Mekong River is home to more species of giant fish than any river on Earth. This 200 pound specimen was captured by fishermen as it migrated out of the Tonle Sap Lake and into the Mekong River on Nov. 15, 2003.

Dr. Zeb Hogan / University of Nevada, Reno

Seven-striped barb for sale at a market in southern Laos in 2010. The seven-striped barb is one of the Mekong largest fish, growing to 200 pounds and about 5 feet in length. It is listed as endangered by the International Union for Conservation of Nature. As recently as 1989, the seven-striped barb was reported as “extremely abundant” in the Mekong, but it appears to have experienced a significant decline since. The seven-striped barb would be further impacted by the Xayaburi dam, potentially blocking access to the fish's spawning areas.

Dr. Zeb Hogan / University of Nevada, Reno

Fishermen work the confluence of the Tonle Sap and Mekong Rivers in Cambodia in January 2003.The Mekong River is the most productive inland fishery in the world, fishermen harvest about 2.5 million tons of fish per year worth an estimated $3 billion to $6 billion. The 60 million people living in the Mekong River basin get the majority of their protein from fish and have some of the highest per capita fish consumption rates on the planet.

Dr. Zeb Hogan / University of Nevada, Reno
Khmer man with a giant stingray, Himantura chaophraya, 
along the Mekong River near the Cambodia/Vietnam border in 2002.  The disk of this fish measured 202cm and 413cm from the tip of its nose to the end of its tail.  Himantura chaophraya may be the largest species of freshwater fish in the world.  More species of giant fish occur in the Mekong River than any other river on Earth.  Populations of the giant stingray and other large-bodied Mekong fish are in decline.

A fisherman in Cambodia holds up the tail of a giant freshwater stingray, which are rumored to grow to 1,000 pounds and approximately 20 feet in length. This specimen was caught in December 2002 and measured almost 14 feet in length. The giant freshwater stingray, which was only discovered 20 years ago, is just one of almost 1,000 species of fish that live in the Mekong, a hotspot for freshwater fish biodiversity, second only to the Amazon.

Dr. Zeb Hogan / University of Nevada, Reno

The Khone Falls area is one of the most important sites for migratory fish – and people who depend on them for their livelihoods – in the entire Mekong River Basin. Over 200 species of fish occur at the falls. Every year, millions of fish struggle to climb the falls, and fishermen in the area harvest them in huge numbers.

Dr. Zeb Hogan / University of Nevada, Reno

People of the Mekong have invented all manner of ingenious ways of catching fish, many of them adapted to a specific site, flow and time of year. These lee traps at the Khone Falls in southern Laos, captured on June 2, 2010, are an excellent example: fishermen construct the traps in the dry season when water levels are low to catch fish at the onset of the rainy season. As the rising water levels cue the fish to begin their migration, the traps are inundated and literally strain the migrating fish out of the water column.

Dr. Zeb Hogan / University of Nevada, Reno

The goonch, or bagrid catfish, is a large predatory catfish that can grow to 600 pounds and 10 feet long. In the Mekong, populations have declined and the largest fish now reach about 6 feet long and 200 pounds. Its life cycle remains a mystery, as is the case with most species of Mekong fish. While little is known about the ecology of the goonch suggests that populations have declined due to the impacts of dams. This photo was taken in India where the goonch is rumored to stalk, attack and kill humans, though that has not been verified.

Dr. Zeb Hogan / University of Nevada, Reno

Two boys carry river catfish along the Tonle Sap River in Cambodia in 2002. Though once a staple food throughout its range, dams and heavy exploitation as a food source have driven river catfish to near extinction in the Chao Phraya River in Thailand and the Thai Mekong. Plans to dam the Mekong could disrupt the life cycle of river catfish, which is migratory and appears to rely on flow or water quality to facilitate migrations, cue spawning and aid in the dispersal of young fish.

Dr. Zeb Hogan / University of Nevada, Reno
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