In the 1970s hundreds of paddlefish were caught each year by fishers on the Yangtze River.
Then, in the 1980s, the population dropped dramatically, Wei said.
The culprit for that loss can be found by taking a 20-minute boat ride up the river from the city of Yichang to the giant Gehzouba hydroelectric dam.
The dam, completed in 1983, divided the Yangtze River into two sections, cutting off the migratory route of the paddlefish.
"The paddlefish travel long distances, from their forage grounds in the middle and lower part of the Yangtze River—and sometimes the coastal waters—to their spawning grounds in the upper river," Wei said.
"The dam separated the feeding area from the spawning ground."
The spawning process for paddlefish is particularly sensitive because females do not become sexually mature until they are seven or eight years old, he added.
The newly built Three Gorges Dam, the largest hydroelectric dam in the world, which sits 30 miles (48 kilometers) upriver from the Gezhouba Dam, has further reduced paddlefish habitat, Wei said.
Two more dams are now being planned for the upper reaches of the Yangtze River.
Last Animal Caught
Fisheries biologist Zeb Hogan was also aboard Wei's boat on his recent ride up the Yangtze.
Hogan heads the National Geographic Society's Megafishes Project, a three-year program to assess the conservation status of the world's largest freshwater fishes.
(See related story and photos: "Megafishes Project to Size Up 'Real-Life Loch Ness Monsters' [July 24, 2007].)
(National Geographic News is a division of the National Geographic Society.)
The plight of the Chinese paddlefish underscores the urgent need to protect the river giants, said Hogan, who is a National Geographic Emerging Explorer.
"Here is what is perhaps the world's largest freshwater fish, and it's close to extinction," he said.
An 11-foot (3.3-meter) paddlefish was caught by fishers in December 2002, Wei pointed out. It died after 29 days in captivity.
The following month, a 12-foot (3.5-meter) paddlefish was caught in Yibin in the upper Yangtze.
Fisheries law enforcement officials immediately contacted Wei. During the eight hours it took him and his crew to travel to Yibin, Wei gave suggestions to officials on how to handle the fish, which survived.
Before it was released back into the river, Wei planted a location transmitter on the paddlefish.
Wei has since lost the signal, but he believes this fish is still alive.
"These fish can live for maybe 50 years," he said. "I'm sure it's still there."
Wei and Hogan have agreed to embark on a joint expedition next year to look for Chinese paddlefish.
Wei believes the upper Yangtze provides a possible last refuge for the fish and that there might be up to a dozen individuals left.
"That area has many deep pools and underwater caves where the fish can hide," he said.
Wei vowed not to retire until he finds a paddlefish.
"I have another 20 years to go," he said. "I'm not giving up that easily."
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