'Giant Fish' Faces Big Trouble in China

Biologist Zeb Hogan is getting a close-up look at one of the world's largest freshwater fishes: the Chinese sturgeon. \

The sturgeons can grow up to 16 feet or 5 meters long and weigh almost 1,000 pounds.\

HOGAN: It's a big fish ... strong ... tail free ... can really whip around.\

The Chinese sturgeon may be powerful, but this giant species is also in big trouble.\

Its home, the Yangtze River in China, Asia's longest river, is increasingly threatened by heavy boat traffic and pollution.\

Hogan is leading the National Geographic Society's Megafishes Project, a three-year study to document the status of the 20 or so species of giant fish found in rivers and lakes around the world. \

More than a fifth of the world's known freshwater fish species have become extinct or gravely threatened in recent years.\

Megafishes are often the first ones to suffer from overfishing or habitat loss.\

Today there may be less than 1,000 adult sturgeons left in the Yangtze River.\

The construction of the Ghezouba Dam in the early 1980s blocked the migration route to the spawning grounds of the sturgeon.\

The new Three Gorges Dam, the largest hydroelectric dam in the world, will present another threat to these giant fish.\

HOGAN (at Dam): From the fish's perspective, nothing worse than a dam ... no spawning ground left for the sturgeon.\

Each year at least 10 sturgeons are also killed after being hit by boat propellers.\

Researchers like Wei Qiwei of the Yangtze River Fisheries Institute are locked in a race against time to save the giant fish.\

Here at a hatchery outside Jingzhou, Wei and his colleagues are running a breeding program to enhance the sturgeon stock.\

WEI AND HOGAN: 1/2 million larvae producing fingerlings.\

Researchers may yet save the Chinese sturgeon, but for an even larger Yangtze giant, the Chinese paddlefish, it may be too late. \

In late 2002, Dr. Wei and his team attempted to rehabilitate one of the last paddlefishes captured in the wild.\

It had been injured by a boat, and died in captivity less than 30 days after its capture.\

The paddlefish can reportedly grow up to 23 feet or 7 meters long and weigh more than half a ton.\

But no paddlefish has been seen since 2003.\

Wei believes there may still be a dozen paddlefish in the Yangtze, perhaps hiding in caves and holes in the upper parts of the river.\

WEI: No fish (yet), but we use a fish finder to find what could be a Chinese paddlefish. We found some signals.\

His 60-foot research vessel is equipped with a tank and a crane ready to rescue any giant fish that he might find.\

If the search fails, this may be the closest we'll ever get to see the Chinese paddlefish again.\