Giant fishes threatened with extermination

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An article in the latest issue of the journal Science highlights the plight of giant freshwater fishes.

In the article by Richard Stone, entitled "The Last of the Leviathans", the extinction threats to some of the world's largest freshwater fishes are highlighted.

The article also discusses the hope that a three-year "Megafishes Project" sponsored by the National Geographic Society and undertaken by University of Nevada fisheries biologist Zeb Hogan, would be able to protect these fishes threatened by overfishing and habitat degradation.

A number of the largest freshwater fish species (about 20 species that reach 200 cm and beyond, and weigh in excess of 100 kg) are found in the Mekong River, and this is where Hogan's research has begun.

This includes the Mekong giant catfish, Pangasianodon gigas, which is threatened by both overfishing (the flesh of this species is highly prized in Thailand, fetching up to $15 per kilogram) and habitat degradation in the form of large dams that threaten to disrupt the spawning migration of this species and proposed schemes to dynamite and dredge the presumed spawning ground of this species in order to improve river navigability.

In Chiang Khong in Thailand, fishermen landed 20 individuals of this species in 1999, none in 2001"2003, seven in 2004 and four in 2005.

A voluntary fishing moratorium was imposed in 2006, and this year, all individuals caught are strictly for research purposes: any giant catfish caught are tagged and released in return for cash.

Other giant freshwater species for which information is scarce and under the threat of extirpation include the Pirarucu, Arapaima gigas, of south America, a species that must surface to gulp air every 15 minutes or so.

This need to surface makes them vulnerable to harpoon fishing and the average capture size has been drastically decreasing in recent decades.

It is believed that there are more than one species of arapaima, and some of these undescribed species are in danger of going extinct before they can be scientifically studied.

The Chinese paddlefish, Psephurus gladius, is a giant freshwater fish species that may already be past the point of no return.

Habitat modification, pollution and heavy boat traffic along the Yangtze River may already have effectively doomed this species to extinction.

The situation for some of the giant freshwater fishes is brighter, thanks to topography, and rarely, sound management.

The giant perch, Lates angustifrons, in Lake Tanganyika has "...a huge, deep lake to hide in and relatively low-technology fisheries methods to contend with," according to Peter McIntyre, a fish biologist at Wright State University.

In North America, sound management has saved the Lake sturgeon, Acipenser fulvescens, from extinction. However, these cases are rare and many of the other giant species remain severely threatened.

The plight of large freshwater fishes has attracted little attention until recently.

According to Stone: "Unlike pandas, their cuddly appeal is nil" and according to Hogan: "People have a hard time sympathizing with fish". Hopefully, Hogan's research will be able to make an impact.

According to the article, some experts believe that the Mekong is a key battleground in the fight to save the giant fishes: "...Hogan's success at translating concern into action may mean the difference between a resurgence in the wild and a gloomy existence as the last living representatives of their species."

For more information, see the article: Stone, R (2007) The Last of the Leviathans. Science 316, 1684"188.