Why these mysterious gray dolphins are covered in a lifetime of white scars

Nature · Published 3 October 2026 · Updated 25 October 2026 Swipe more like this →

In short: Risso's dolphins are the ocean's most heavily scarred cetaceans. As they age, their dark skin fades to a ghostly white, etched with a permanent record of battles and encounters. These deep-diving predators, often found in pods of up to thirty, possess a unique anatomy that defies typical dolphin expectations.

The Risso's dolphin, or Grampus griseus, is a medium-sized cetacean found in temperate and tropical oceans globally. Unlike many of their relatives, they possess a remarkably low number of teeth—typically just two to seven pairs, located exclusively in the lower jaw. This dental arrangement is highly unusual among cetaceans, yet it serves them well in their nocturnal pursuit of cephalopods like squid, octopus, and cuttlefish.

Their most striking feature is their appearance. Newborns are born with a dark cape and saddle, but as they mature, their skin lightens to pale gray or white. This transformation is accompanied by heavy, permanent scarring. While some marks come from interactions with prey like lampreys or cookie-cutter sharks, many are the result of intraspecific tooth-raking. Because these dolphins lack the ability to repigment their skin, these scars accumulate over a lifespan that reaches at least 35 years, potentially serving as a visual display that signals dominance and reduces the need for physical conflict between males.

These animals are masters of the deep, frequently inhabiting waters near the continental shelf edge and slope. They are capable of diving to at least 1,000 feet and holding their breath for 30 minutes, though they often prefer shorter, shallower dives. While they are not currently endangered in the United States, they face significant global threats, including entanglement in commercial fishing gear, underwater noise pollution, and direct hunting in regions such as Japan, Indonesia, and the Caribbean. Their movements remain somewhat enigmatic, though researchers believe their distribution is closely tied to the migration of their preferred prey and shifting oceanographic conditions.

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