The Dall’s porpoise (Phocoenoides dalli)
Some of your may remember the work in progress views for these guys, now finally onto the interweb they go. Another commission for the lovely people at Porpoise Conservation Society, as part of our porpoise species series. Usually one scientific illustration suffices, but with huge sexual dimorphism, two distinct colour morphs and very different calf colouration, no less than six illustrations came into being.
They were lots of fun to paint, and it was interesting to get to know the species better. Truei-type Dall's porpoises occur only east of Japan, while the Dalli-type extends all across the northern Pacific. Within the Dalli-type are again two morphs: in the East the white marking is long, in the West it is short. The change is gradual, and find their extremes on either side of the Pacific. Dalli- and Truei-types are not definitively separated either: a Dalli-type female from the Eastern Pacific was once found carrying a Truei-type calf.
I also tried to show as much individual variation as possible, while still keeping the illustrations representative. Some examples: the Dalli-type male is dotted with fine black spots. Most Dall's have a couple around the edges of their white markings, but some animals are simply covered in them. The four adults also show different degrees of lightness. The Truei-type female is very dark, with almost no white markings to speak of. The Dalli-type female is as light as they get: extensive markings on her pectoral fins, and the normally vague grey tailstock marking is a solid white.
The calves are a different story altogether. Unlike their adult counterparts, newborn and juvenile Dall's porpoises show clear, almost dolphin like markings on their body and especially face. Interestingly, Dalli-type calves display a Truei-type like marking in creamy grey. On very young calves this area can be very light, making them almost look like a Truei-type animal.
Another interesting thing is the males 'manliness'. The more macho a male, the more convex shaped the flukes and the more forward-canting the dorsal fin. For some reason Truei-type males are usually displayed as smaller and more flimsy than Dalli-type males, even though there is no difference in size. So here I reversed the stereotype, giving the Truei-male more manly fins. Another interesting thing is the influence of pose on their perceived shape: although the Truei-male's tailstock seems slimmer than that of the Dalli-male, both have the exact same measurements.
