An international team of marine biologists has recorded an astounding round-trip journey made by a gray whale who ventured from Russia's east coast to the southern tip of Mexico's Baja California peninsula – and then all the way back. At 14,000 miles (22,500 km), it's the longest migration of a mammal ever recorded.
For the study, the results of which now appear in the journal Biology Letters, researchers from the Oregon State University Marine Mammal Institute and Russia's A.N Severtsov Institute for Ecology and Evolution tracked the progress of seven North Pacific gray whales using satellite-monitored tags. Three of the whales were tracked from their main feeding ground off Russia’s Sakhalin Island across the Pacific Ocean to the North American west coast. A female, dubbed Varvara, made her way south to Baja, Mexico.
To the surprise of the researchers, Varvara then made a round-trip journey after venturing to all three major North American breeding areas typically occupied by eastern gray whales. Her 172-day, 14,000 mile trip transpired between November 24, 2011 and February 2, 2012, and is now the longest mammal migration on record.
The realization that the critically endangered western gray whale interacts with the eastern gray whale, which is not endangered, is altering the marine biologists' conception of both whales and their status as two distinct species. There's also concern that the population living on the western side of the Pacific may now be extinct.
“The fact that endangered western gray whales have such a long range and interact with eastern gray whales was a surprise and leaves a lot of questions up in the air,” noted Oregon State University marine biologist and study lead author Bruce Mate in a release. “Past studies have indicated genetic differentiation between the species, but this suggests we may need to take a closer look.”
Once thought extinct, the western gray whale is now estimated to consist of 18,000 individuals. But if these two species represent one distinct species, it could be a sign that the whales are restoring their former historic range along the North American west coast.
Another possibility is that some eastern gray whales might actually be western grays. If that's the case, then the number of true western gray whales is even smaller than assumed.
Read the entire study at Biology Letters: “Critically endangered western gray whales migrate to the eastern North Pacific”.