Risso's Dolphin

Risso's Dolphin (Grampus griseus) is a unique marine mammal and the only member of its genus. It is closely related to various other dolphins and whales such as pilot whales and false killer whales. Characterized by their distinctive white scars, Risso's dolphins typically reach about 3 meters (10 feet) in length. They inhabit a wide range of marine environments, preferring areas along continental shelves. This preference is largely due to their diet, which is primarily composed of cephalopods like squid. These dolphins are impressive divers, able to reach depths of up to 600 meters (nearly 2,000 feet) in pursuit of their prey.

Socially, Risso's dolphins travel in pods of 10 to 50 individuals, where strong bonds are formed. At times, they may gather in larger "super-pods" that number in the thousands. The composition of these groups often varies by age and sex, with long-term associations observed particularly among adult males, while younger dolphins frequently change groups.

Risso's dolphins are identifiable by their solid build and a large dorsal fin that tapers towards their tail. They have a bulbous head marked by a vertical crease. Younger dolphins exhibit a grey to brown coloration with a lighter underside and distinctive white areas. As they age, their nonwhite areas become darker and eventually lighten again due to scarring. These scars, which are a result of social interactions and competition, are more prevalent in older individuals and may serve to deter competition among males.

Their range covers the 🇮🇳 Indian, Pacific, and Atlantic Oceans, as well as seas such as the Baltic and Mediterranean. Risso's dolphins prefer waters with depths of 400 to 1,000 meters and temperatures between 10°C and 20°C. They rely on echolocation to hunt, often planning dives based on prey distribution, as observed in studies from the Azores. Social behaviors at the surface include interactive displays like tail slaps and spy-hopping, potentially for communication or mating purposes.

These dolphins face threats similar to many marine species, such as pollution from noise and plastics, as well as entanglement in fishing gear. While protected under certain laws like those in the 🇺🇸 United States, they are still hunted in some parts of the world.

Named after Antoine Risso, the species was first scientifically described by Georges Cuvier in 1812. The original specimen is preserved in France, and the naming has undergone revisions since its initial designation.

Reproduction in Risso's dolphins involves a gestation period of 13 to 14 months. Females reach sexual maturity between 8 and 10 years, while males mature at around 10 to 12 years. These dolphins can live up to 39.6 years. Occasionally, they have been known to hybridize with bottlenose dolphins, though this is rare and lacks specific evolutionary benefits.