The Sulphur Bottom of the Pacific. Sibbaldius sulfureus,
Cope. The Humpback of the Pacific. Megaptera versabilis, Cope.
The sulphur bottom whale is another name for the blue
whale. As these animals pass through tropical waters, a "bloom" or form
of algae grows on their underside, the green algae on a bluish background
giving a yellow tinge. This earned them the alternative name. On leaving
tropical waters for more temperate or polar seas, so the algae cannot
grow any more in the colder waters and so dies off leaving the whale
as it was originally.
For many years it was not recognized by all that the
blue whale and the sulphur bottom were in fact the same animal and so
they were given different Latin and common names.
Image courtesy NOAA