Here is T.J. Bass’s book The Godwhale, this novel was nominated for a Nebula Award. Cover art by Paul Lehr.

Rorqual Maru was her name. She was a harvester – a vast plankton rake without a crop, abandoned by Earth Society when the seas died.

Well over 600 feet long, a marvelously complex combination of biology and mechanics, she had been left to rot in the dead and sterile sea.

But the sea was no longer dead and Rorqual Maru had lived. The gigantic organism moved, bearing on her back a small island of palms and shrubs, acquired over the inactive centuries. Mankind was about to be served –

But mankind had forgotten all about Rorqual and her kind…

(from the back cover)