"Much of what we know about Risso's dolphin, also called grampus, comes from studying stranded animals. They inhabit deep tropical and warm-temperate waters worldwide, usually where the water is deeper than 180 m, making them hard to study. The remains found in stomachs show they prey upon squid exclusively. Scars are often found on their skin, which may be the results of wounds produced by squid beaks and tentacles. Some researchers believe these marks may also reflect the highly physical ways these dolphins interact - by slapping, splashing, and leaping on one another. Risso's dolphin is highly social. Hundreds of them have been seen swimming on the surface, leaping clear of the water, and ""bow-riding"" on waves, sometimes with Pacific white-sided dolphins and northern right whale dolphins."

Links:
Mammal Species of the World