A grey whale usually seen more towards Russian shores is taking a swim across the Bering Sea towards Alaska.

American and Russian researchers are tracking the male western Pacific grey whale (nicknamed Flex), that has now made it more than halfway across the Bering Sea, reaching shallow continental shelf waters. As it's not known where these particular whales usually are at this time of year researchers cannot confirm if this crossing is unusual. It is known where these animals aer during their summer feeding season which is predominantly around Sahkalin Island at the south end of the Sea of Okhotsk.

Eastern Pacific grey whales, also called California grey whales, are a familiar sight in Alaskan waters. They feed in the Bering, Chukchi and Beaufort seas in summer and migrate down the West Coast each winter to breed, mostly in the bays of Baja California. They were taken off the endangered species list in 1994 and their population currently stands at around 18,000.

Western Pacific grey whales are the only baleen whales which are mainly bottom feeders. They are the second most threatened species of large whales (with an estimated population of around 130 animals), behind North Pacific right whales. Almost all of the western Pacific grey whale population in are known on sight from photo catalogues, most have also been biopsied for genetic analysis.

In previous centuries Western grey whales were decimated by whaling and feared to be extinct in the mid-1970s. A population was rediscovered off Sakhalin Island (the Russian Island north of Japan) and has been monitored since the mid-1990s. There is concern for this population as Sakhalin Island has become the site of major offshore oil and gas activities. They also face threats from accidental entanglement in fishing gear, with five female western grey whales dying by entanglement over the past four years.

Flex was tagged in September with a tracking device the size of a small cigar. Researchers thought that the whale would travel down the Asian Coast and perhaps have final destination of the southeast China Sea or spend time off the Kamchatka Peninsula, however from the point where the Aleutian Islands intersects with Russia's Kamchatka coast, the whale began swimming east instead. Satellite monitored radio tags have lasted as long as 385 days on a grey whale and average four months. The tag on Flex has been attached about 100 days however it cannot be predicted how long this particular device will remain attached.

This is not the first time a grey whale has shown up in a surprising place as last year one was discovered in the Mediterranean Sea off Israel.

Marine Connection supporters can track the rare western Pacific gray whale here (this will be updated each Monday)