A Rare Encounter with Mating Harbour Porpoises – 05/19

Harbour Porpoise have a pretty wild sex life: They mate promiscuously, and the speed and energy involved in a mating attempt often results in fast aerial displays otherwise rarely observed in this species

On a sunny day in the spring of 2019, our marine mammal observers were treated to an unexpected display of Harbour Porpoise mating behaviour. It’s not that we hadn’t seen that before ─ porpoise aren’t shy at all when it comes to mating. (We had previously recorded mating attempts in pictures and on video and contributed to related research.)

But what we saw in May was nothing short of a porpoise orgy!

A large group showed up, milling around, foraging… ─ and then the scene erupted into chaos. It took us a moment to realize what was happening when we saw some of the animals break the surface and go all splashy on us.

(We had just told a group of park visitors that Harbour Porpoise tended to be the non-splashy kind.)

But it wasn’t just one excited male showing off what it really means to have testes that make up 4-6% of their body mass during the mating season. (For the record, that’s huge! It means that a 50 kg male could have testes weighing about 2 kg!)

No, this time they seemed to have an all-hands-on-deck approach. Harbour Porpoise have mating strategy called “sperm competition”, where females mate with multiple males. And oh did they do that.

Mating attempts are notoriously difficult to capture in pictures. It happens in seconds, it takes a small miracle to accurately guess where in the water it’s going to happen next. A lot of practice is required, and even more luck to get just one good shot of the action. But with every so many animals joining in on the action, we were quite successful.

Males copulate by positioning their ventral sides on the females’ left side. We managed to capture that quite well in some of the pictures…

-Porpoise Conservation Society

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