The interchangeable use of the terms “dolphin” and “porpoise” contributes to confusion regarding the occurrence and taxonomy of two distinct species.
Dolphins and porpoises are marine mammals – warm-blooded, have lungs (air-breathing), have hair (visible when very young), bear live young, and nurse their young. Adding to the confusion is the dolphinfish (Coryphaena hippurus) which is cold blooded, has gills and spawns eggs.
When fishing enthusiasts refer to “dolphin”, they often mean the dolphinfish, 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 fishers refer to the mammal dolphin, they often use the term “porpoise”.
The only species of porpoise we see in North Carolina is the harbor porpoise (Phocoena phocoena), generally stranded dead, occasionally dying, during the winter, mostly north of Cape Hatteras. The porpoise’s normal range is concentrated north of us. Historically, what was/is referred to the “porpoise fishery” on North Carolina beaches, 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 year-round. The table below highlights differences between bottlenose dolphins and harbor porpoises in NC. The color graphic compares the external appearance of the 3 species. In the Bonehenge Whale Center we recently completed a skeletal display of a harbor porpoise to compare with that of a bottlenose dolphin.
Bottlenose dolphin (Tursiops truncatus), Beaufort, North Carolina – 26 Dec 2014. Photo by Keith Rittmaster under NOAA/NMFS permit.
Harbor porpoise (Phocoena phocoena) (29 March 2014, Virginia Beach)
Harbor porpoise (Phocoena phocoena) skeleton