Inflating Dead Dolphin Penises Reveals The Mystery Of Marine Mammal Sex


Tom Hale


Tom Hale

Senior Journalist

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist

Two bottlenose dolphins having sex in the Genoa Aquarium in Genoa, Liguria, Italy.  Vladimir Wrangel/Shutterstock

Dolphin genitalia, the final frontier. Science knows very little about marine mammal sex, especially when it comes to female reproductive organs involved. Since it’s so tricky to observe marine mammals get down and dirty in the wild, or even in an aquarium, how would you go about studying this?

Well, this team of scientists from Dalhousie University led by Dara Orbach knows how. Their novel method involves inflating the penis of the dead marine mammals with saline to mimic an erection. They then insert this stiff penis inside corresponding vaginas, and use CT scans to see what exactly is going on in there. All the specimens were found in the US and died of natural causes.


The team presented their preliminary findings a few months ago but now their study, Genital interactions during simulated copulation among marine mammals, has been published in the journal Proceedings of the Royal Society B in all its glory.

In their latest study, they employed their revolutionary techniques on four species of marine mammal: bottlenose dolphins, common dolphins, harbor porpoises, and harbor seals. 

The penises (brown) and vagina (green/blue) of (a) harbor porpoises (Phocoena phocoena), (b) common bottlenose dolphins (Tursiops truncatus), (c) short-beaked common dolphins (Delphinus delphis), and (d) harbor seals (Phoca vitulina). Dara Orbach et al

Their findings showed that the biomechanics of marine mammal sex is actually pretty complicated.

“Whales, dolphins, and porpoises have unusual vaginal folds, spirals, and recesses that the penis and sperm must navigate through to successfully fertilize the egg," Orbach explained at the American Association of Anatomists annual meeting in April 2017.


This is found to be particularly true with harbor porpoises and common bottlenose dolphins, where researchers found the penis and vagina were an "antagonistic fit," as the female vaginal fold appears to act as a barrier to penile penetration. These twists and turns actually make it harder for the sperm to meet the egg, meaning the female can control which males are able to fertilize her eggs. This means only the best mates with the “strongest” genes are selected.

The study also explains another advantage to these rather unusual vaginas: “In addition, the folds may serve as a mechanism to prevent seawater from entering the female reproductive tract, as seawater is lethal to sperm in at least one species of cetacean.”

The learning doesn’t stop there. The researchers also hope these discoveries will be used to develop better biomimetic vaginas that are capable of gathering a higher volume of ejaculate from males during semen collection procedures.

An image reconstructed from CT scans showing how the penis of the common bottlenose dolphin (red) fits within the intricate folds and turns of a bottlenose dolphin vagina. Dara Orbach/Dalhousie University


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  • dolpin sex