blubber in aquatic mammals

[sundancer]

Do all aquatic mammals have a layer of blubber?

[wildwood]

With some exceptions, yes. Fat is an ideal insulator against the cold. There are some reports of blue whales with 12 inch blubber, but 6-8 would be more usual.
Exception include the marine otter which is insulated with a coat of extremely dense hair. Wether you want to include the marine otter as aquatic is up to you.

[scoobysoo]

I am a mammal and have about 4 inches of blubber, sometimes more after pizza. Although I am not aquatic, I do have regular baths so would therefore consider myself semi aquatic. Good luck in your quest for blubber knowledge (PS see u at work tomorrow) ;)

[New Forester]

Yes, almost all full-time aquatic mammals have blubber. Many part-time ones don't -- for example, otter, beaver, muskrat, mink, platypus etc. I too can only think of the sea otter as the exception. (I'd certainly call marine aquatic...) Its thick fur traps an air layer for insulation, and it regularly blows air from its mouth into the fur to keep it topped up.