Ocean Sunfish

These massive, disc-shaped fish inhabit open oceanic and coastal waters, often drifting with currents in the epipelagic zone while feeding on jellyfish, salps, and small fish. The most reliable sighting cue is their distinctive dorsal fin breaking the surface as they lie on their sides — a behavior called basking, likely used for thermoregulation after deep dives — which can be mistaken at a distance for a shark fin, though the fin here appears to flop or oscillate rather than cut steadily through the water. Warm months from late summer into autumn offer the best opportunities along temperate coastlines, particularly from headlands, whale-watching vessels, or kayaks in calm, glassy conditions when surface disturbance is minimal and fins are easy to spot.