All About Grampus Griseus
Risso’s Dolphins (Grampus Griseus) are the only dolphins in the genus Grampus; their name was derived from Niçard naturalist, Antoine Risso.
They are a relatively large dolphin species, with adult lengths averaging at around 10′ and some individuals can grow over to be 13′. They don’t look like a “typical” dolphin, as they have a blunt shaped head and don’t have a long, protruding beak.
Risso’s dolphins can be highly active at the surface exhibiting a range of behaviours like breaching and spyhopping. They usually do not bow ride, but they can be seen travelling in the wake of ships.
Younger Risso’s are usually darker in color and older individuals appear more white. When they are born, infants are dark grey on their sides and back, with cream colored areas on their bellies and around the beaks. In older calves, the nonwhite areas darken to nearly black, and then lighten (except for the always dark dorsal fin).
As they grow older, white linear scars begin to cover their bodies. These are derived from scratches from squid (their primary prey) and from other Risso’s dolphins during social interaction; these scars eventually cover the bulk of the body, hence why older individuals appear whiter.
Most individuals have two to seven pairs of teeth, all in the lower jaw. Rather than teeth in the upper jaw, there are “sockets” that fit each tooth on the lower jaw. This is a common characteristic for cetacean that feed heavily on squid (i.e. Sperm Whales).
They are found worldwide, in temperate and some tropical waters. They typically reside in deep water, fairly close to land. Here in Southern California, we see them once or twice every few months. They are considered to be one of the 5 most commonly seen local dolphin species (the others are Long and Short beaked Common Dolphin, Bottlenose Dolphin and Pacific Whitesided Dolphin).
Photos/Footage by Mark Tyson and Craig DeWitt.