Risso's dolphin in wild population seem to obtain scratches with aging. What is causing them and what do they mean?
[ From Jefferson et al. 2015, Marine Mammals of the World, 2nd edition, p 212: "At sea, the best identification characteristic is the coloration and scarring. Adult Risso's dolphins range from dark gray to nearly white, but are typically covered with white scratches, spots, and blotches. Many of these are thought to result from the beacks and suckers of squid, their major prey, but others may be caused by the teeth of other Risso's dolphins. If fact, this species is the most heavily-scarred of all the dolphins." ]
Although little is known about these animals, they seem to obtain these scars from scratching in fights with their prey, giant squid, and from the teeth of other Risso's dolphin.
Most of the linear scars are thought to be caused by intraspecific interactions, e.g. scratches from each others teeth, though some more circular or oval scars are thought to come from squid. Cookie cutter scars are not commonly described for Risso's dolphins though they are common in other whales and dolphins.
Encyclopedia of Marine Mammals. 2002. W.F. Perrin, B. Wursig, J.G.M Thewissin. Academic Press: New York.