for National Geographic News
This is the fourth story in a continuing series on the Megafishes Project. Join National Geographic News on the trail with project leader Zeb Hogan as he tracks down the world's largest freshwater fishes.
A ferocious and even cannibalistic predator (cannibalism photo), taimen can grow more than six feet (up to two meters) in length and can weigh up to 200 pounds (91 kilograms).
But like many other freshwater giants around the world, the taimen is now threatened with extinction.
Scientists last month wrapped up a four-year study of the fish in a 60-mile (100-kilometer) stretch of the Eg and Uur rivers.
Their results show that the taimen, also known as the giant Eurasian trout, is now too rare to support sustained commercial or recreational harvest.
"This fish is not like other trout and salmon species," said Zeb Hogan, a fisheries biologist with the University of Reno in Nevada.
Waist-deep in the clear, fast-moving waters of the Eg, Hogan prepared to release a newly tagged, 44-inch-long (112-centimeter-long) taimen back into the river.
The fish, which takes up to nine years to fully mature, can live for 50 years, said Hogan, who is a National Geographic Society Emerging Explorer. (National Geographic News is owned by the National Geographic Society.)
"We only see a few animals this size per mile in the river, so if you remove one of them, it's going to take a long time before it can be replaced," he said.
Earlier this year Hogan launched the Megafishes Project, a three-year effort funded by the National Geographic Society to document the 20-some species of freshwater fish found around the world.
The project looks at fish that are at least 6.5 feet (2 meters) in length or 220 pounds (100 kilograms) in weight.
But 70 percent of such species are threatened with extinction as a result of habitat destruction, overfishing, and pollution, Hogan said.
The taimen, the only fish species from the salmon and trout family large enough to qualify as a megafish, has already been harvested to the brink of extinction in neighboring China. Its numbers are also shrinking rapidly in Russia.
Mongolia's pristine Eg-Uur river basin now remains one of the last strongholds of healthy taimen populations.
A main reason is that Mongolians are traditionally nomadic herders who don't fish. But that could soon change.
"We're seeing a cultural shift in Mongolia with Western-style outdoor adventure and recreational fishing becoming more popular," said Brant Allen, a researcher with the University of California Davis, and a member of the taimen science team.
"There is evidence that poaching of the taimen is increasing," he said.
In their four years of studying the taimen, the scientists have tagged about 400 specimens to learn more about the fish's migrations patterns and population.
The scientists estimate that the population in their study area is about 2,000 catchable-size fish, which is defined as 26 inches (66 centimeters) or longer.
Radio and acoustic tagging also show that the fish are prone to stay in one place, though when they do move they can travel as much as 50 miles (80 kilometers) from their home.
"The fact that they have a predictable home territory makes them vulnerable to harvest, because people will know where to go to hunt for big fish," Hogan said.
"People see large fish in one spot, then return to that area again and again, harvesting every fish."
The cannibalistic instincts of taimen became apparent when Allen, the UC Davis researcher, recently examined a 32-inch-long (81-centimeter-long) taimen he had just caught at a bend in the Eg.
"It has a really large bite mark on him," Allen said, pointing to a wound below the fish's dorsal fin.
"They exhibit quite a bit of stress when they're fighting on the line, and another fish probably saw that as a weakness and came up and just bit him."
But the taimen doesn't just eat its own kind. It also consumes a range of mammals—rats, ducks, even bats—that may be unfortunate enough to end up in the water.
They have also been seen hunting in packs, earning them the nickname "river wolves."
Unsurprisingly, taimen are a major draw for anglers looking for a chance to hook the biggest trout on Earth.
American companies such as Sweetwater Travel of Livingston, Montana, charge tourists about 5,500 U.S. dollars each for a week of taimen fishing.
But anglers must practice catch-and-release fishing. They must use single, barbless hooks to catch fish and then release them back unhurt.
"A taimen can be caught over and over again without being harmed," Allen said.
Scientists, private fly-fishing outfitters, and local nonprofit organizations generally support the creation of a catch-and-release fishing reserve in the Eg-Uur Watershed.
"We welcome sport fishing in Mongolia because it helps our economy," Erdenebat Eldev-Ochir, executive director of the Taimen Conservation Fund, said at his office in Ulaanbaatar, the Mongolian capital.
The faith-based nonprofit organization spearheads the sustainable fishing effort.
"We just want to make sure it's done in a way that protects the taimen population," Eldev-Ochir said.
The Mongolian government is now considering a proposal put forward by the conservation fund that would make it illegal to catch and kill taimen anywhere in Mongolia.
To Hogan, the battle to save the taimen has become personal.
"We see the same fish living in one pool year after year," Hogan said.
"We've tagged them, we've given them names. We want to see them remain in the river."
The taiman's plight is particularly urgent, Hogan said, because the population in Mongolia's Eg and Uur rivers is still more or less intact.
"Unlike some of the other megafishes, like the Chinese paddlefish, which may already be gone, here we actually have a real chance to protect [this] fish before it disappears."
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES