I recall looking at the Gulf Coast from a 10-story balcony. Along came a school(?) of stingrays, perhaps 6-8 of them. From the 10th -floor (and 100 feet from the water) they still looked HUGE!. They were pretty close in too - just a bit farther than where the waders were. Much larger than than the people. (The beach dropped off pretty quick). It was an amazing thing to seem them “flying” like a squadron.
Probably mantas