The interchangeable use of the terms “dolphin”, “porpoise”, and “mahimahi” contributes to the confusion regarding the occurrence and taxonomy of three distinct species. Dolphins and porpoises are marine mammals – warm-blooded, have lungs (air-breathing), and bear live young. The mahi-mahi (Coryphaena hippurus) is a fish – cold blooded, has gills (extracts oxygen from water), and spawns eggs.
When fishing enthusiasts refer to “dolphin”, they often mean the dolphin fish, AKA “mahi-mahi” or “dorado”. Mahi-mahi are fun to see and catch, delicious to eat, and if you see “dolphin” on a menu (at least in the US), that’s what you’ll be ordering. When those fishers want to refer to the mammal dolphin, they often use the term “porpoise”.
The only species of porpoise we could possibly see in North Carolina waters is the harbor porpoise (Phocoena phocoena), generally dead, or dying, during the winter. Their normal range is concentrated north of us. Historically, what was/is referred to the “porpoise fishery” on North Carolina beaches, actually targeted bottlenose dolphins, not porpoises or fish.
Bottlenose dolphin (Tursiops truncatus) is the only species of dolphin you are likely to see healthy in North Carolina’s coastal and estuarine waters. Dolphins grow much larger than porpoises, have a large, falcate dorsal fin, and have a prominent beak (rostrum). Other species of dolphins occur further offshore, but that’s for a future post.
The graphic below will help clarify differences in the 3 species.