This, like my “You Otter Know” blog, is aimed at clearing up species confusion and offering some support to my fellow marine educators.
Yes, I am writing this for much needed educational porpoises. Sorry! I will attempt to restrain myself from further bad puns (but I am counting on you, the readers, to come up with some doozies).
Oh the number of times I have had the joy of an exchange like this:
Me: “Look, a porpoise!”
Response: “Ja, ja, een delfin!” or “Oui, oui, un dauphin” or “Ja, ja, een dolfijn” or “Yes, yes, a dolphin!”.
Me (armed with images like those below): “Nein – een schweinswal” / “Non – un marsouin” / “Nee – een bruinvis” / “Nope – it really is a porpoise!”
It is so understandable that there is significant confusion. The words dolphin and porpoise were, colloquially, used as if they were synonyms into at least the 1970s.
But, dolphins and porpoises are more distinct than lions and tigers. Lions and tigers are not only in the same family but in the same genus. Dolphins and porpoises are in different families, having diverged around 15 million years ago.
The differences between porpoises and dolphins span from fin and head shape, to behaviour, vocals and average group size.
In many resources, the three distinctions that are most often provided are – the difference in the shape of the teeth, rostrum (snout) and dorsal fins. But really, the first two are not likely to help you in the field! When at sea, in addition to dorsal fin shape, group size and behaviour are probably going to be of use more use in discerning porpoises from dolphins.
In the table below, I provide a summary of the differences with great thanks to Uko Gorter for his illustrations. This information will likely be useful too in making clear how it is that Orca are dolphins – the biggest member of that cetacean family.
Off the coast of British Columbia, in addition to Orca, commonly there is only one species of dolphin (Pacific White-Sided Dolphins) and two species of porpoise (Harbour Porpoises and Dall’s Porpoises).
Dall’s Porpoises most often get misidentified as dolphins because they are larger than other porpoise species and because they are far less cryptic e.g. when going at full speed at the surface at ~55 km/hour, there is a very distinctive spray of water known as a “rooster tail” and, they do sometimes interact with boats – bow riding like dolphins do. Please note that I very consciously choose to use “cryptic” as a descriptor rather than the very anthropomorphic term “shy”. Harbour Porpoises can be difficult to detect, but I assure you, that this highly promiscuous species is anything but “shy”!
Yes, I used the term on porpoise!
Uh oh, I did it again! I almost made it to the end of the blog without another bad pun. 🙂
More information aimed at discerning species below.
For information on the hybridization of Dall’s and Harbour Porpoise see Carla Crossman’s research here.
For more on how to discern British Columbia’s cetacean species, please see here for information from the BC Cetacean Sightings Network.
Below – illustrations of additional porpoise species and known ranges.
Related TMD Blog: Cetacean Gender – Male or Female? How to Know?