Dolphin or porpoise? Porpoise or dolphin? What’s the difference? It’s probably the most common identification mistake made when it comes to cetaceans on the coast of B.C. It’s plain to see how easy it is to mix-up many dolphin and porpoise species: they have similar characteristics including size, colouration and behaviour. Even the names are often used interchangeably in everyday language. So what’s the deal?
It’s not just a difference in colloquial name, dolphins and porpoises are actually entirely different families of cetaceans. In fact, as the Encyclopedia of Marine Mammals points out, porpoises and dolphins are “as different as horses and cows or cats and dogs”.
Porpoises belong to the Phocoenidae family. There are only six species of porpoises in the entire world, two of which live in B.C. waters (Dall’s porpoises and harbour porpoise). Oceanic dolphins, however, belong to the large Delphinidae family, which consists of at least 36 species worldwide! In B.C., eight species of delphinids have been recorded, including killer whales (the world’s largest dolphin), Pacific white sided dolphins, Risso’s dolphins, Northern right whale dolphins, false killer whales, long-beaked common dolphins, striped dolphins, and pilot whales (possible).
Despite their different evolutionary histories, the two families have developed such similar body plans that often we can’t tell them apart from a quick glance. The main distinguishing feature is actually their teeth. Dolphins all have cone-shaped teeth, whereas porpoises have flat, spade- shaped teeth. While this distinction may be apparent on a skull in a museum, it’s a tricky one to make in the field. After all, dolphins and porpoises don’t go about flashing their pearly whites!
On the water, there are a few other morphological traits that can help you distinguish a dolphin from a porpoise. While not a hard and fast rule, dolphins usually have a more curved dorsal fin, while porpoises have a more triangular one. Dolphins also tend to have a longer rostrum (the pointy ‘beak’ part of their face), while porpoises have a much shorter one, although there are definitely a few exceptions this this rule (including the non-existant rostrum of the Risso’s dolphin!). Additionally, Dall’s and harbour porpoises in B.C. rarely leap fully out of the water, while this is a behaviour that is observed regularly in dolphins, particularly the common Pacific white-sides seen along the coast.
Acoustically dolphins and porpoises differ quite a bit too. Dolphins vocalize in a range audible to the human ear. If you were to drop a hydrophone in the water around dolphins, you would be able to hear a cacophony of sound (listen to them here: Pacific white sided dolphin sound). Conversely, porpoises vocalize at a much higher range that we simply can’t hear. A recent study in the journal PLOS ONE by Beedholm and colleagues showed that porpoises produce high frequency clicks that are restricted to a narrow band of frequencies, while those of a dolphin are not. Their theory is that porpoise echolocation evolved this way to avoid killer whale predation- essentially staying “under the radar” by making sounds killer whales cannot hear. They propose that dolphins have not evolved this high frequency echolocation because they employ other strategies, such as large group size or incredible speed, to avoid killer whale predation.
From teeth to acoustics, dolphins and porpoises are indeed very different animals. Distinguishing between the two just takes a bit of practice. Note the length of their rostrum, the curve of the fin, and any surface behaviours, such as the full body leap! Learn more about the dolphin and porpoise species in B.C. here and remember to report any that you see!