Featured Image Credit: Manx Whale and Dolphin Watch
By Eva Gruber
Risso’s dolphin (Grampus griseus) is a relatively common species of dolphin that can be found in subtropical and temperate waters across the world except for the Atlantic. With a relatively large (up to 10 feet long – in fact they are the largest dolphins) light gray body, short rostrum, and upturned smile, these dolphins look comical in much the same way that a beluga does.
They tend to stick to deeper waters where they can pursue their prey, deep water squid, which they hunt mostly at night as their prey engages in diurnal migration up the water column. Being squid specialists, they have lost most of their teeth with only between two and seven pairs in the lower jaw. Who needs teeth when you can swallow your squid whole?
Risso’s are relatively abundant, with the population residing just off the continental shelf of the United States to be around 60,000 individuals. Another population of Risso’s recorded 175,000 in the east Pacific and another 80,000 in the west Pacific. No global estimate currently exists, although with multiple healthy populations this species is currently considered by the International Union for Conservation of Nature to be of Least Concern (the lowest conservation rating).
In the United States, Risso’s dolphin is often seen off the shore of California. They are common species observed during whale watching trips. One marine biologist located in La Jolla reports that she has often seen Risso’s engaging with whales and that they do so in a mischevious manner. Perhaps they are encountering the whales as they move over the dolphins’ deep water territories, and the dolphins are reacting. They may be defending their pod and their young by investigating strange animals.
The marine biologist reports that the encounters do not seem to be aggressive, and may indeed be curiosity-fueled playful events. She has seen pods of Risso’s approach and circle intruding whales. After some time, the dolphins then might brush up against the massive animal. The gray whales seem to respond by taking up a defensive posture or fleeing the area by picking up their swimming speed and changing course.
Risso’s, in fact, seem to be a very social species whose interactions are driven by touch. Risso’s dolphins are unique in their coloration. While their skin is grayish colored, as they age their skin becomes crisscrossed with whitish slashes.
These are scars from cuts inflicted mostly by other Risso’s dolphins, but also by their squid prey. Recent research suggests that this species has one of the most unique social structures for cetaceans, with individual groups segregated by sex and age. They typically gather in groups of up to 30 individuals, although every once in a while super-pods of hundreds of individuals have been seen. They can often be seen engaging in acrobatic leaps at the surface.
Another one of our ocean’s fascinating creatures!