Risso’s dolphins (Grampus griseus) are found in temperate and tropical seas, usually offshore near the continental shelf. Their appearance inshore is uncommon, but in numerous instances, groups have moved into inshore areas where they have been seen repeatedly over a fixed period of time. In the Pacific Ocean, their range extends from British Columbia down to the tropics. They are regularly seen off of Monterey Bay, California. In BC, they have been seen travelling together with Pacific White Sided Dolphins.
Adult Risso’s dolphins can reach a length of 4 meters (13 feet) and they have a grey colour with a dorsal fin, a fluke, flippers, and eye patches that are all darker compared to the rest of the body. The body also has extensive white scarring. The scars can be scratches, splotches, or circular marks and, in some animals, can be so extensive that the entire body appears to be white. The scarring may come from bites from other Risso’s dolphins, squid bites, or parasites. Risso’s dolphins also have a white anchor-shaped patch on their ventral/chest area (from throat to stomach). The dorsal fin is tall, curved and located near the middle of the back. The flippers are relatively long and thin, and pointed almost straight back.
Risso’s dolphins usually take short dives of a few minutes. However, they are capable of diving to at least 1,000 feet (300m) and holding their breath for 30 minutes. They feed primarily on squid and other cephalopods (e.g., octopus and cuttlefish) as well as on fish (e.g., anchovies). They usually travel in groups of a dozen or less, but they have been observed to be in larger groups varying from around 50 to a few hundred.
Risso’s dolphins (Grampus griseus) Specifics:
up to 4 m (13 ft)
Up to 500 kg (1100 lbs)
Gray coloured body
Extensive white scarring
Dorsal fin, flippers, fluke, and eye patch all darker than rest of body
Tall curved dorsal fin
Scarring from squid or bites from other dolphins
Flippers are long and thin that point straight back