The large beast is a Dactylobatus clarkii or Hookskate.
Dactylobatus clarkii, Clark's fingerskate or the hookskate, is a medium-sized but poorly known, deepwater skate/ The distribution of the hookskate is considered patchy and covers the western central and southwest Atlantic. Usually on muddy bottoms of the continental slope at depths of 315–915 metres (1,030–3,000 ft)
The guy threw it back, btw. I mean, he's not a monster and I think the animal is endangered. But enjoy. Maybe next time you go to the ocean, you can meet a massive underwater sea creature that is a terrifying living fossil.
Edited to add:
The wikipedia article you link to says it isn't a hookskate but actually a roughtail stingray.
D'oh. Thanks for pointing that out, KorbenDallasBathroomPass