Whats what?

These pic's were taken by Captain Colm Claire Senior Master Stena Europe when he was master of a cruise ship plying the worlds oceans. These were taken off the coast of Brazil some years ago and have puzzled him ever since! The pictures are of the same thing but taken as the ship was passing by. It was visible from the Bridge,  was stationary and did not move for over twenty minutes.

Its pretty obvious its a whale fluke (tail) much as you might see as a whale such as a Humpback or Right whale dives... thing is this did not dive, just hung there. My thought for what its worth is that the animal was dead but if so it would fill with gas and not be floating tail up... unless it had been chopped in two! Maybe someone better acquainted with the habits of these animals has a more plausible explanation? let us know at seatrustwales@gmail.com