Rare, tagged western gray whale located near Monterey PATH: Behemoth named Flex swims past central California.

SAN JOSE, Calif. -- The central California coast was the unlikely host over the weekend of an enormous, foreign seafaring traveler on a marathon sprint to parts unknown.

Flex, a 13-year-old western gray whale from the chilly Russian waters off Sakhalin Island, is the first of his kind to be outfitted with a satellite tracking tag -- and his trans-Pacific dash is a surprise to scientists. The tracking tag, about the size of a cigar, reports Flex's location to scientists each day. They've calculated his average swimming speed -- roughly 4 mph -- and determined that the he travels about 100 miles each day.

"Flex is somewhere around San Francisco or Monterey right now, if he's kept up that speed," Bruce Mate, director of the Marine Mammal Institute at Oregon State University said on Friday. "These whales swim 24 hours a day. It's not an eight-hour shift. They don't feed during their migration, and they're really moving along."

In October, scientists finally tagged Flex after weeks of typhoons and bad weather. They had hoped to tag 12 whales as part of an effort to understand the endangered western gray whale, and Mate hopes to affix more tags in the coming year.

With only 130 known individuals, the western gray whale is second only to the North Atlantic right whale in terms of large marine mammals approaching extinction. Not much is known about the population's behavior except that they summer off the Russian coast, filtering invertebrates from mouthfuls of salty ocean mud.

When Flex began his oceanic odyssey, scientists were shocked by his range and route. Flex has traveled more than 5,300 miles so far, and he zoomed almost directly across deep, open ocean waters, to Alaska before turning south, displaying behaviors atypical of the better known, eastern Pacific gray whales. That population of about 20,000 is robust and doing well.

San Francisco-based nonprofit Pacific Environment has been following Flex's progress with enthusiasm. "I've been tracking him every week. I wait for the update," said interim executive director Leah Zimmerman, referring to the website (http://mmi.oregonstate.edu/Sakhalin2010) where the public can follow Flex's travels. Since the early 1990s, Pacific Environment has been working with partners in Russia to help protect the whale's habitat around Sakhalin Island. Offshore oil, gas and seismic testing are threatening the already delicate population, and Zimmerman hopes studies like this will help conservation efforts.

"The scientists who monitor the western gray whales know many of them by sight and have nicknames for them because there are so few," Zimmerman explained. "We need to know where these majestic mammals spend their time so we can activate conservations measures."

Though Flex is providing the first glimpse of the western gray's habits, scientists still don't know where he is going, whether such long journeys are normal and if he is traveling with other whales.

"That's the wonderful thing about tagging studies," Mate said. "You put the instruments on the animals and they tell their own stories. They go where they go."