ANCHORAGE, Alaska: A highly endangered whale that spends summers off Russia has moved into water off British Columbia after crossing the Bering Sea and passing the Aleutian Islands.

The 13-year-old, male western Pacific gray whale dubbed Flex is being tracked by US and Russian researchers.

Its last location was logged Thursday about 400 miles (645 kilometers) off the coast of British Columbia, said Bruce Mate, director of Oregon State University’s Marine Mammal Institute.

Mate said it was possible the whale’s satellite tag had fallen off, or that bad weather interfered with transmissions.

Western Pacific gray whales are the second-most threatened species of large whales after North Pacific right whales. Only 130 of the gray whales remain.

In contrast, there are about 18,000 eastern Pacific gray whales. Those whales breed and give birth in warm water, mostly along Baja California, and migrate north to spend summers on feeding grounds in Alaska’s Bering, Chukchi and Beaufort seas.

Western Pacific gray whales spend summers near Sahkalin Island at the south end of the Sea of Okhotsk near Russia. Little is known of their winter habits. North America waters were not high on lists of suspected winter sites.

Last year, researchers from Oregon State and the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences had hoped to tag 12 western Pacific gray whales but were limited by typhoons and gales to one on the last day of field work.

Flex was tagged Oct. 4. He spent more than two months feeding near Sakhalin Island and moved across the Sea of Okhotsk to the west coast of the Kamchatka Peninsula.

Within a few weeks, the whale rounded the southern tip of the peninsula and left the east coast of Kamchatka across the Bering Sea, averaging about 4.5 mph (7.25 kph).

On Jan. 13, Flex was about 80 miles (128 kilometers) north of Alaska’s Pribilof islands. He turned south and was tracked on the south side of the Alaska Peninsula near the Shumagin Islands, possibly crossing the Aleutians through Unimak Pass or False Pass, two common routes for eastern grays during migration.

A week ago, he was in the Gulf of Alaska about 400 miles (640 kilometers) south of the Alaska fishing community of Cordova. Researchers don’t know where he wants to go.

‘‘Our assumption right now, and it’s very much an assumption, is that he’s going to intersect the primary migratory pathway for the eastern gray whales, which is closer to shore by far than his current path,’’ Mate said.

If his goal is to head south, he’s certainly turned the corner to be more efficient, Mate said. His trajectory now puts him on a course to be close to shore along the central Oregon coast by Thursday.

Researchers are prepared to shadow the whale if he gets close to shore.

Mate hopes swells are blocking transmissions from the whale. Satellite monitored radio tags have lasted as long as 385 days on a gray whale but average four months. The tag transmits four hours a day to conserve battery power.

‘‘When animals are coming up to breathe, they basically surface in the trough,’’ he said. ‘‘The large swells on either side of him tend to mask the transmissions.’’

The chances of finding the whale if the tag is off are minimal. The public can track the whale on Oregon State’s website.