As members of different families of the order of cetaceans, dolphins and porpoises, both of the suborder Odontoceti—or toothed whales—are closely related marine mammals, not to be confused with each other. When people refer to dolphins they most likely envision the playful, large bottlenose dolphin (Tursiops truncatus), commonly seen at aquariums or other tourist attractions. The bottlenose dolphin is part of the family of toothed whales called Delphinidae. Porpoises, on the other hand, are of the family of toothed whales called Phoceonidae. People are most likely to encounter the harbor porpoise, or Phocoena phocoena, in areas close to shore.
Because of similarities in shape, color and movement, and the fact that both mammals travel in groups, distinguishing dolphins from porpoises can be confusing. They also sound similar, in that both dolphins and porpoises are among cetaceans that use the highest frequency emissions to communicate, hunt and navigate, compared to other species of cetaceans.
When trying to determine whether a specimen is a dolphin or porpoise, consider some of the key differences between these two families of whales.
Where They Live and Behavior Around Humans
Dolphins are found throughout the northern and southern latitudes of the Atlantic, Pacific and Indian oceans, are quite friendly, and are likely to interact with humans and play in the waves around ships. There are even species of dolphins that live only in freshwater rivers, such as the pink dolphin of South America (Inia geoffrensis).
Porpoises, on the other hand, live in coastal areas in more northern latitudes, such as around the perimeters of North America, Canada, Europe and Japan. Sometimes they enter rivers, but don’t stay. They are more shy than dolphins, more likely to disappear when encountered, preferring not to surface around boats and humans, or jump out of the water, as dolphins do.
Physical Differences
There are several key differences in the bodies of dolphins and porpoises:
- Body size. Dolphins tend to be larger and have more tapered bodies than porpoises, which are smaller, chubbier creatures.
- Shape of the snout. Generally, a dolphin’s snout is a prominent beak, whereas a porpoise has a short, rounded snout that resembles more of a point than a beak.
- Dorsal fin shape. The dorsal fin of a dolphin is taller, more pointed and curved back than a porpoise’s, whose dorsal fin is a lower triangle with a rounded-off tip.
- Shape of the teeth. Dolphin teeth are more cone-shaped, but porpoise teeth are flatter, like a spatula.
Use a Guidebook to Identify Species
Because of a multitude of variations in coloring and markings among all kinds of dolphins and porpoises, using a guidebook to compare general body color, and the shape and color of markings, is probably the best way to distinguish individual species while in the field. As with identifying any kind of animal in nature, where often only a quick glimpse occurs, look first for the shape, size and color of specific identifying features (such as fins, beaks, or markings like a stripe or patch), and take note of movements or behaviors. This way, if the animal does not come into view again, you have committed to memory the most clear indicators, rather than relying on a general memory of the whole.
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