Big fish that (sadly) aren't getting away

Many an angler has waxed poetic about "the big one" that got away. But Zeb Hogan has a real fish tale: an actual catch of the world's largest known freshwater fish.

It happened as the University of Wisconsin biologist was trekking across Mongolia, part of an 18-month scientific effort to study the world's largest fish. While there, Dr. Hogan got the message he had been hoping for: an e-mail describing a newly caught catfish the size of a grizzly bear.

At six feet long, and 636 pounds, the Mekong giant catfish netted by local fisherman in a remote village in northern Thailand was a contender, Dr. Hogan realized immediately. But was it the biggest? He pored over his records on the giant species before reaching his conclusion: It was the biggest living freshwater fish on record.

Until it died.

That's the challenge that Hogan, director of the Great Fishes Project, often must endure as he travels across six continents investigating the reasons these huge fish are disappearing.

"At the turn of the century they used to catch thousands of huge catfish like this each year - today it's five or 10," Hogan says of the Mekong giant catfish. "We've got to understand better the problems these huge fish face. They have large habitat requirements, they mature later, and they often migrate across wide areas - all of which makes them more vulnerable."

The Mekong giant catfish is Southeast Asia's rarest and largest freshwater fish. It lives in what is still the world's most productive fishery, feeding 73 million people who live along the river. But dynamite blasting to open up channels, dams constructed further north in China, and heavy fishing have combined to create a dwindling population of the sort of giant caught last month, he says.

Fish like the Mekong giant, which is considered "critically endangered" by the IUCN International World Conservation Union, are biologically important and are considered by scientists to be telltale species for problems in the ecosystem. Where fisheries are under pressure from pollution or overfishing, top predators typically disappear before the smaller fish.

Funded by the World Wildlife Fund and the National Geographic Society, the Great Fishes Project aims to study the globe's largest freshwater fish - those that grow to 220 pounds (100 kilograms) or more than 6.5 feet long.

Hogan's investigations, if he can find added funding, will take him across 10 of the globe's most diverse freshwater ecosystems in 18 months. He'll be looking for 30 species, among them sturgeon, goliath catfish, huge carp, gar, and enormous stingrays. Once analyzed, his data will provide a baseline against which future losses or gains will be measured.

"We know the historic range of these huge animals and where they've been extirpated," says Melanie Stiassny, research curator of fishes at the American Museum of Natural History in New York. "This is very important work. There are so few places left on the globe where migrations of these giant animals can take place unimpeded. [Hogan] will find areas of the world where the rivers run free, where there are refuges, and we'll be able to concentrate our efforts on conserving those areas."

For the past six years, Hogan has worked with fishermen in Cambodia and Thailand, educating them on the importance of returning the largest fish to the Mekong River - and compensating them for their catch. Despite the death of the catfish caught in June, which was going to be returned to the river, Hogan still hopes for other even bigger catches - which can then be put back in the river.

He recalls fondly standing face-to-fin in the river with a 600-pound Mekong giant catfish a few years ago.

"I think there are other fish in the Mekong at this moment that are larger," he says. "We haven't found them yet, but doesn't mean they aren't there."