Harbour Porpoise Phocoena phocoena 

Harbour porpoises are relatively small compared to other dolphins. They have small, rounded heads with no beak and dark lips and chin. Equipped with robust, stocky bodies, they have predominantly dark brown backs with a pale grey or white underside, blending halfway up their sides. A small triangular fin set just past the centre of the back is one of its very distinctive features. Image: Andrew Reding (Flickr).

Find out more: Whale and Dolphin Conservation, The Mammal Society, Suffolk Wildlife Trust, iNaturalist