I just Googled the phrase "fell porpoise" and came up with nothing. Nada. Zippo. Not a single webcomic. Not a single blog. Not a single hipster making a pun along the lines of "no one could fathom his fell porpoise...no matter how much it chittered and squeaked." Nothing.
Interwebs, you have failed me.
You have failed to come up with every possible inane notion or idea before I have a chance to. SO I CLAIM THIS ONE. THE FELL PORPOISE IS MINE! MINE I TELL YOU! BWAHAHAHAHAHA!!!!
Take that, Interwebs.