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Depending on the species, whales can migrate up to twenty-two and a half thousand kilometers across oceans. And as for why, there have been a few reasons proposed over the years -- from availability of food, to warmer water helping them get pregnant.

But according to one group of researchers, it might actually be part of some whales' skincare routines. Humpback whales may be the most famous long-distance travelers, and the current hypothesis for why is that they will swim to cooler waters in the summer to feed, and to warmer waters in the winter to give birth to their young. Scientists think that the warmer waters might offer some whale species a safer place to give birth because there are fewer predators there at the time.

Alternatively, the milder temperature might be less shocking to newborn calves. This “feed and breed” idea explains why baleen whales migrate, but not all whales do it for the same reasons. Take killer whales for example.

In 2019, researchers published a study that tracked and took photos of a group of sixty-two [62] killer whales as they migrated north from Antarctica to warmer seas. Some of their warm-water migrations were really quick, like not enough time to pop out a little one. What's more, they observed killer whale moms with calves in Antarctic waters, suggesting they weren't traveling north to give birth in warmer areas.

The adult whales were also tracked traveling fast and at shallow depths. That didn't match up with the whales' normal feeding behavior, where they dive deep in search of food. So the researchers surmised there had to be another reason for the trips.

And some of their previous research provided a clue. See, in 2011, researchers from that same group had observed that, at some times of the year, the whales would be covered in a thick, yellow gunk from the buildup of algae. Yet at other times, they'd be clean as a whistle.

So they proposed that these killer whales were taking a tropical vacation of sorts where they would ditch the crud. Because it's pretty chilly down there in Antarctica, it's thought that killer whales limit circulation to their skin to prevent them from losing too much body heat. But skin kind of needs that blood supply to churn out new skin cells and refresh itself.

Whales and dolphins who live in more temperate places can slough off their skin continuously. But in cold water, that might mean too much heat loss. So for these killer whales, traveling to warmer waters might mean they can open those blood vessels, molt their old skin, and zip back home squeaky clean -- all without losing too much heat.

The authors suggest that other whales living in cold waters -- including humpback whales, belugas, sperm whales, and gray whales -- might migrate for the same reason. Now, one paper is definitely not enough to claim that all whales migrate as part of their beauty regimen. Plus, even if molting is one reason to travel, it doesn't mean the other reasons -- like decreased predation -- aren't true.

Still, there's definitely some evidence for the idea of the ocean spa day -- and as reasons for taking a vacation go, it's pretty relatable. And our patrons definitely deserve a spa day, especially this month's President of Space,. SR Foxley!

Your support seriously means so much to us. If you want to help support SciShow and see if you might be President of Space someday, check out patreon.com/scishow. {♫Outro♫}.