This video, recorded at sea between Denmark and Sweden, is called Harbour Porpoise having fun at our boat.
Translated from Ecomare museum on Texel, and the Utrecht University veterinary department in the Netherlands:
Thursday, December 18th, 2014
For the first time biologists have found out that porpoises may also have twins. During an investigation of the cause of death of a stranded porpoise, researchers at Utrecht University discovered two female fetuses in the womb of this cetacean. The discovery of twins in a porpoise has not been previously described in literature. With other whales and dolphins this is not a common phenomenon either. So, a unique find!
The porpoise stranded on April 13, 2011 on the beach of Texel. It was a dead adult female of 151 centimeter and nearly 50 kilogram.