"He was a porpoise."
A Harbour Porpoise at an aquarium.
GNU Free Documentation LicenseA Harbour Porpoise at an aquarium. - Credit: Malene Thyssen

 Porpoises are cetaceans, closely related to whales. They are similar to dolphins but are smaller with less pronounced beaks. They are generally bluish-black with white undersides and may grow between 1.2 to 2m long.

 

Dolfinarium
Creative Commons AttributionDolfinarium - Credit: stefanoost