Could be shark, tuna, ray, or anything that is counter-shaded that hangs out along the surf zone. Looks too chill to be a dolphin, and if that is a pectoral fin it is long and has a black tip. Or it could just be another damn surfer (thanks David!).
One thing's for sure, Kelly 'I would be honored to be eaten by a shark' Slater has zero f*cks to give.