Today at class of Marine Animal Pysiology, talking about flotability and migration, the teacher told us: why do whales need that quantity of fat if they are travelling in tropical/subtropical waters? Well, the answer is simple: fat also acts as an inspecific method of flotability. Many animals have similar methods, Portuguese Manowars store air instead of fat, in order to keep floating. This is not an adjustable method, and it's not specific, meaning the floating fluid is uniformally distributed everywhere in the body. I didn't know that, and I've been a whale nerd since my childhood. Guess you can't equal university!