http://www.sciencemag.org/news/2020/02/scientists-say-they-ve-cracked-mystery-why-whales-migrate-and-it-s-all-about-healthy

Killer whales with yellow skin restore their white patches after migrating to warmer waters to molt.

Some people travel across oceans to seek warm, healing waters in spas or coastal resorts. It turns out that whales are likely making their annual migrations for much the same reason: to maintain healthy skin, according to a new study out today.