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/ Source: NBC News

The western gray whale now holds the record as the mammal with the longest known migration, researchers say.

A female western gray whale swam from Russia to Mexico and back again — a total of 13,988 miles (22,511 kilometers) — in 172 days, according to a new report.

Until now, the title of the longest-migrating mammal belonged to the humpback whale (Megaptera novaeangliae), which migrates up to 10,190 miles (16,400 kilometers) round trip as it travels between its breeding grounds near the equator and the food-rich waters of the Arctic and Antarctic, according to Guinness World Records.

Gray whales, like other whale species, are known for their long-distance migrations.Omar Torres / AFP - Getty Images

But the new report shows that a female western gray whale (Eschrichtius robustus) named Varvara (the Russian equivalent of the name Barbara), has stolen the record. Researchers placed satellite-monitoring tags on seven western gray whales living off Russia's Sakhalin Island, where the mammals feed every year. Varvara was the only whale whose tag stayed intact throughout the entire journey, said the study's lead researcher, Bruce Mate, the director of the Marine Mammal Institute at Oregon State University. [Quest for Survival: Photos of Incredible Animal Migrations]

Western gray whales are critically endangered; they were once even thought to be extinct, Mate said. Before the new study, little was known about these animals' migratory paths, and many researchers suspected that the whales migrated in a loop from Russia to the South China Sea.

Instead, the tagging study shows that Varvara swam to Mexico.

"She crossed the Bering Sea, the Gulf of Alaska [and] the lengths of the North American continent to get down to the Baja breeding calf lagoons that are used by eastern North Pacific animals," Mate said.

The study was published online by Biology Letters.

— Laura Geggel, LiveScience

This is a condensed version of a report from LiveScience. Read the full report. Follow Laura Geggel on Twitter. Follow LiveScience on Twitter, Facebook and Google+.