Risso's dolphins in Hawai‘i
Adult Risso's dolphin (Grampus griseus) off the island of Hawai‘i. Photo (c) Robin W. Baird. We've seen Risso's dolphins on only nine occasions between 2000 and July 2014, with all sightings off the island of Hawai‘i. They are probably seen so infrequently 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). Analyses of sightings by depth taking into account effort show that Risso's dolphins primarily use very deep water (>3,500 m) in Hawai‘i. 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, with a median group size of 4 and a range from 1 to 24 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, but have been slowly accumulating photos to eventually establish a catalog.
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:
- Baird, R.W., D.L. Webster, J.M. Aschettino, G.S. Schorr and D.J. McSweeney. 2013. Odontocete cetaceans around the main Hawaiian Islands: habitat use and relative abundance from small-boat sighting surveys. Aquatic Mammals 39:253-269. Download PDF copy
- Baird, R.W. 2008. Risso's dolphin Grampus griseus. Pages 975-976 in Encyclopedia Of Marine Mammals, Second Edition. Edited by W.F. Perrin, B. Wursig and J.G.M. Thewissen. Academic Press, San Diego, CA.Download PDF copy
- Baird, R.W., and P.J. Stacey. 1991. Status of the Risso's dolphin, Grampus griseus, in Canada. Canadian Field-Naturalist 105:233-242. Download PDF copy
All photos are copyrighted and should not be used without permission.