The southward journey takes 2 - 3 months and the whales remain in the lagoons for 2 - 3 months allowing calves to build up thick layers of blubber for the northward migration. (nps.gov)
For example, whale's milk is especially high in fat because whale babies need a thick layer of blubber to keep warm in cold waters. (drbenkim.com)
In order to thrive, they have a thick layer of blubber. (newbabynewpaltz.com)