Adult Risso's dolphin (Grampus griseus) off the island of Hawai‘i. Photo by Annie Douglas. We've seen Risso's dolphins only seven occasions between 2000 and 2009, probably so infrequent because groups are usually far from shore (ranging from 3 to 61 kilometers; average = 37 km) in deep water (range 1,500 m to 4,700 m; aveage = 3,482 m). Risso's dolphins in Hawai‘i don't flee from boats like striped dolphins, but they are very difficult to get close to. Group sizes are typically small (ranging from 1 to 12 individuals). With our low encounter rates and difficulty in getting close enough for good photos, we do not currently have a photo-identification catalog of Risso's in Hawai‘i, and have been unable to collect any genetic samples.
A juvenile Risso's dolphin off the island of Hawai‘i. Photo by Daniel Webster. Although they are lighter in color when first born, calves darken to almost black, then lighten as they mature.
Our sightings have spanned the period from April through November, and we have little research effort in the deep offshore waters during the period from December through March, so Risso's dolphins may be present throughout the year.
For more information on Risso's dolphins see the following publications:
All photos are copyrighted and should not be used without permission.