> 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. “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.”