The only member of its genus
Risso’s dolphin stands alone in Grampus, distinct enough from the other dolphins in the Delphinidae family to earn its own genus. It’s a large, heavy-bodied dolphin found in scattered numbers along both the Pacific and Atlantic US coasts. More than 10,000 confirmed records add up across that whole range.
A squid specialist among dolphins
Recorded prey is dominated by squid and octopus: sharpear enope squid, football octopus, southern shortfin squid, and several other deep-water cephalopods. That diet sets Risso’s dolphin apart from the fish-eating dolphins it sometimes shares water with. It likely dives deeper and hunts differently to reach squid living well below the surface, relying more on sound than sight to track prey in dark water.
Two coasts, recorded through every month
Records span California in the west to Florida, Georgia, North Carolina, Virginia, Maryland, Massachusetts, and New York in the east, with California carrying by far the largest share. Sightings hold up across the whole year but climb through summer, peaking in August, likely tracking both prey movement and when observers are out on the water.
Few recorded predators
Great white sharks are the recorded predator of Risso’s dolphin. That’s a short list, and it may reflect a dolphin large and fast enough to avoid most other hunters rather than a genuinely predator-free life.
Reproduction and lifespan
Risso’s dolphins mature around age ten, carry a pregnancy for about 13 months, and typically raise one calf at a time, spaced roughly two years apart. Wild individuals have been recorded living past 40.
Conservation
The IUCN lists Risso’s dolphin as Least Concern. It remains widespread along both US coasts, and its preference for squid over fish means it competes less directly with commercial fisheries than many other dolphins do.
