Rissos Dolphin

(Grampus griseus)
Rissos Dolphin Santa Barbara Channel
Risso's Dolphin Two Cows Two Calves - Photo Credit: Bob Perry

The Risso's dolphin is in a genus by itself, although it is related to pilot whales and false killer whales. Also known as the Monk dolphin, this dolphin species is found around the world in temperate and tropical waters. They are found in areas of the Pacific Ocean, so keep your eyes open when we're out around the Channel Islands. They do tend to prefer deeper waters near the coast, living in waters that may range between 1,300 and 3,300 feet deep. Researchers don't know much about their migratory patterns, if they have any.

Risso's dolphin is the largest dolphin species, with males usually being larger than females. While typically 10 feet long, they may grow to a little over 13 feet and weight 600 to 1,100 pounds. They have a characteristic bulbous head that has a vertical crease in the front of it, with a large body and dorsal fin that tapers to a tail that tends to be narrow.

Like many toothed whales, Risso's dolphin tends to be scarred, but these cetaceans tend to be more heavily scarred with linear marks that tend to arise from social interactions. The older members of the species tend to be whitish in color, while infants are born a darker color. These younger dolphins tend to be grey or brown on their back and cream-colored on their belly, with an anchor-shaped white mark between their pectoral fins and around their mouth. As they age, the non-white areas will darken on these dolphins, before they eventually lighten.

Unlike dolphin species that often feed on cephalopods and small fish, Risso's dolphin feeds almost entirely on squid, although in some areas of the world, such as Scotland, their preferred food is curled octopus. They tend to feed nocturnally, and one population near Santa Catalina Island coexists with pilot whales, which all feed on the squid population, although they don't seem to interact with each other.

Similar to other dolphins, Risso's dolphins are social animals and are typically found in groups. They can form "super-pods," although they are more commonly found in groups of 10 to 50 dolphins. Within the super-pods, they seem to form smaller and stable sub-groups, often similar in characteristics such as age and sex. The younger animals tend to move more commonly between groups. When you're watching these animals, you may see acrobatics above the water, and some will come up close to boats, particularly in areas where they associate boats with their squid prey.