And as a poster on that forum points out:
I’m not so convinced this is even a shark. The dorsal seems rather too curved for a shark, and the tail and pectoral fins, though mostly obscured by the water, seems too small somehow and further foward (respectively) than I would expect to see on a shark.
And another post:
That looks like a genuine photograph. The relative position, size and shape of the dorsal fin says dolphin, dolphin and dolphin. Additionally, sharks have a second dorsal fin near the tail, which is missing on dolphins and missing in the photo.
All signs lead to dolphin, and it’s probably a Bottlenose dolphin ( Tursiops truncatus ). They love to ride waves like this.
