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Scientists scour globe in search for world’s largest freshwater fish

Posted: Friday, September 23, 2005

PHNOM PENH, Cambodia — Floating down the Mekong in his dinghy, Zeb Hogan is on the ultimate fisherman’s quest: to find the world’s largest freshwater fishes.

The American biologist’s search is to take him to 10 rivers around the globe including the Nile, Amazon and Mississippi, looking for about 20 species of hulking fish such as the goliath catfish, Chinese paddlefish and North American lake sturgeon — not to catch them, he says, but to save them.

‘‘These big, amazing creatures all over the world, they might be goners, on their way out,’’ he says.

Right now Hogan is on the Mekong that flows through the Indochinese peninsula, looking for a stingray said to weigh over 1,300 pounds — as much as a full-grown longhorn steer.

He knows it’s out there; he photographed one in 2002. And smaller stingrays abound. As he passes villages on riverbanks or floating on the water, he sees children playing with severed stingray tails.

The 2,600-mile Mekong is known for its diversity of river creatures, as well as their size, to judge from places along its banks named the Pool of the Giant Catfish, or the Pool of the Giant Carp. Just last May, fishermen in Thailand landed a Mekong catfish that weighed 646 pounds and was 8 feet, 10 inches long. It’s believed to be the largest freshwater fish ever caught and measured. It ended up on dinner tables.

On his voyages, says Hogan, ‘‘The main question I’ll be asking everywhere is what were populations like in the past, what are they now?’’ He believes, ‘‘you’ll see a pattern that these populations of these large fish species are declining — a lot.’’

These are not aquatic sasquatches he’s looking for, but fish whose existence is proven fact. The goliath catfish is still fairly common, Hogan says, and Wisconsin has a fishing season for lake sturgeon. The Chinese paddlefish is very rare, but a 275-pounder was caught on the Yangtze River in China on Dec. 11, 2003. There are said to be 650-pound carp, but none over about 300 pounds has been seen in recent times, Hogan says.

Almost all maximum lengths and weights come from accounts over the ages by scientists, explorers and taxonomists, and ‘‘in many cases have been verified by present-day scientists like myself. That is, after all, one of the main objectives of the project,’’ Hogan says.

Hogan, of the University of Wisconsin-Madison, is 31 and has worked on the Mekong since 1996. His research is supported by the World Wildlife Fund, the National Geographic Society’s Emerging Explorers Program, and outdoor-gear companies Marmot and Patagonia.

He’ll be working with other scientists studying the creatures, such as a biologist researching the Amazon’s arapaima, which can weigh 450 pounds, and a Texas freshwater guide who will help him study the alligator gar, which can reach 300 pounds.

As they putter down the Mekong, Hogan and his two Cambodian assistants pass constant reminders of the importance of the Mekong’s fish population to the 73 million people living along its banks. People busily mend nets, and at night, dozens of tiny candles in floating containers mark where nets have been laid in the water off Phnom Penh’s riverfront.

Along the way, Hogan and his assistants pepper fishermen with questions and pictures of their quarry.

The fishermen may not have caught or even seen the fish, Hogan said, but often will say they have heard about it being somewhere else. ‘‘Theoretically, that’s supposed to lead us to where the fish are.’’

Not always, though. He says fishermen are hesitant to admit they’ve hooked a big one, for fear of running afoul of Cambodian and international restrictions on hunting rare species. The penalties are small, but the fishermen don’t want the bother.

Hogan expects to finish in December 2006 and give his fish counts to IUCN, the World Conservation Union, which compiles a Red List of Threatened Species — creatures threatened by overfishing, pollution, dams and alien aquatic life introduced by humans.

IUCN lists some of the giants as endangered or critically endangered, but for others, there simply isn’t enough data to judge.

‘‘We have a sense that the world’s largest freshwater fish are disappearing really fast,’’ said Robin Abell, a WWF freshwater conservation biologist. ‘‘We do need to work to understand both the species and the threats to them.’’

‘‘The most exciting part for me,’’ says Hogan, ‘‘is that that no one’s done this before.’’

He believes the stingray ultimately will take the title, but says he will adhere to tough standards.

‘‘If I don’t have a photo or a weight, to me, it’s not legitimate,’’ he said. ‘‘I can’t go just by word of mouth ... fishermen are famous for exaggerating the size of fish that they catch.’’



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