MOSCOW -- When a young man lost both his arms this week in the waters off Russia's east coast, officials and residents initially had trouble believing what had happened. But a day later, when a teenager's legs were ripped up in the same waters, all doubt vanished.
In a region more accustomed to threats from bears, the culprit appears to be a man-eating shark -- possibly more than one.
The authorities have temporarily banned swimming at several beaches in the area, coastal Primorsky Krai, along the Sea of Japan. It was unclear what type of shark attacked in either case, though witnesses and some scientists were leaning toward a great white.
Large sharks have been sighted in the region only rarely, scientists said, and attacks until now were unheard of.
"They said it was a shark, but I didn't believe it," said Andrei Tarasov, who witnessed the first attack and was interviewed by Russia's Vesti television. "I thought they were mistaken until I saw the guy who was attacked. Then there was no doubt."
The first victim, a 25-year-old computer programmer, had been out for an evening swim with his wife on Wednesday at a popular vacation spot near Russia's border with North Korea.
The two, Denis and Polina Udovenko, were aiming for a small rock formation known locally as Yearning Heart Island.
"It was only about 300 feet," Ms. Udovenko said, according to the Interfax news agency. "About halfway there, Denis noticed something in the water and screamed, 'Swim faster, it's a shark.' "
"He beat it on the nose, and it heaved him up and then down," she said. "Then the shark threw him to the surface."
They were hauled in by boaters.
Mr. Udovenko lost a considerable amount of blood and both arms below the elbow, but he survived, the Health Ministry said in a statement.
The second victim, Valery Sidorovich, 16, was attacked about 30 miles away on Thursday. Video images of his rescue that were broadcast on Russian television showed him being taken from a boat on a stretcher, his legs swaddled in bloody bandages.
Late on Thursday, the Russian news media reported a third attack, citing local residents, though officials did not immediately confirm it.
Dmitri Pilipchak, a spokesman for the local branch of the Emergency Situations Ministry, said that there had not been one recorded case of a shark attack in the region until now. "These are the first," he said. In fact, some scientists said they were probably the first in Russian waters in recent history.
Witnesses gave varying descriptions of the shark, putting its size at 6 to 12 feet long. After reviewing the accounts, several scientists said they believed it was probably a great white. Smaller sharks, like the salmon shark and the spiny dogfish, are commonly found in the Sea of Japan, but they do not typically attack humans, said Konstantin Zgurovsky, the marine program coordinator for the Russian branch of the World Wildlife Fund.
While great whites have a very large range and are found all over the globe (not to mention scary movies), they have rarely been sighted in the Sea of Japan, said Dmitri Astakhov, a shark expert at the P.P. Shirshov Institute of Marine Sciences in Moscow. That body of water is home to seals and other shark prey, but not in sufficient densities to sustain large sharks. A hungry great white, lacking its typical prey, Dr. Astakhov said, "could certainly have attacked a human." (For the same reason, overfishing is often blamed for increasing the likelihood of attacks on humans around the world.)
One reason the two victims may have survived, he said, is that sharks actually find the taste of humans off-putting. "A big enough shark can instantly rip off a limb, but as soon as it tastes the meat and realizes that it is not right, it will immediately leave it behind," Dr. Astakhov said. "Victims are often injured, but not killed."
Another draw for a great white might be water temperature. The waters in the region have been several degrees higher than normal, making a more attractive environment for great whites, according to Mr. Zgurovsky.
Russians' blasé attitude toward danger is a source of national pride, and despite the ban on swimming, local news media reported Thursday that beachgoers continued to take to the water.
The local branch of the Emergency Situations Ministry, perhaps expecting that many would flout the ban, posted a shark attack survival guide on its Web site.
"If a shark tries to attack you, fight it off; try to hit it in the eyes and gills," read one advisory. "Remember," read another, "panic could lead to tragic results."
This article originally appeared in The New York Times .