Marine Mammal Species Description

Risso's Dolphin

Grampus griseus

(G. Cuvier, 1812)

Photo credit: Wayne Hoggard NOAA/NMFS/SEFSC

Classification

Order: Cetacea
Family: Delphinidae
Alternate Common Names: Grampus, gray grampus, white-headed grampus

Status: protected under MMPA

Description:

   Length: 9.2-12.5 ft (2.8-3.8 m)
   Weight: 880-1320 lbs (400-600 kg)

Risso's dolphins have a tall falcate dorsal fin and long, thin, pointed flippers. They are generally dark on their dorsal fin, flippers, and fluke, and lighter gray on their sides and back. Their undersides are paler. The bodies of adult Risso's dolphins are commonly covered in scars and markings that are a distinctive feature of this species.

Habitat:

Risso's dolphins occur in temperate and tropical waters typically 1,310-3,280 ft (400-1,000 m) in depth. Some occasionally occur in shallower waters, but usually only in areas where the continental shelf comes close to the coast. Risso's dolphins sometimes occur by themselves, but are more commonly seen in schools of 10 to 50 individuals. Some schools as large as a few thousand individuals have been documented.

Feeding:

Risso's dolphins mostly eat squid, but occasionally they eat fish. Researchers have documented that most of their feeding occurs at night.

Reproduction:

Female Risso's dolphins reach sexual maturity when they are 8-10 years old. Males reach sexual maturity around 10-12 years. Sexually mature individuals are around 8.5-9.2 ft (2.6-2.8 m) in length. Females have calves approximately every 2-3 years. Gestation period is estimated to be around 13-14 months.

Other:

The maximum documented life span for a Risso's dolphin is around 35 years old.

Distribution / Range:

Risso's dolphins occur in temperate and tropical waters worldwide. They tend to occur in cooler waters during summer months.

Similar species:

The extensive scarring on Risso's dolphins makes it easy to destinguish this species from other dolphins.

Notes:

References:

American Cetacean Society. 2004. American Cetacean Society Fact Sheet. http://www.acsonline.org/factpack/RissosDolphin.htm. Accessed January 2012.

Baird, R.W. 2009. Risso's Dolphin - Grampus griseus. In: Encyclopedia of Marine Mammals 2nd Ed. Perrin W.F., B. Würsig, and J.G.M. Thewissen, eds. Academic Press, New York, pp. 975-976. Culik, B. 2010. Odontocetes. The toothed whales: "Grampus griseus". UNEP/CMS Secretariat, Bonn, Germany. http://www.cms.int/reports/small_cetaceans/index.htm. Accessed January 2012

Shelden, K.E.W. 1999. Risso's dolphin, Grampus griseus. In The Smithsonian Book of North American Mammals. Wilson, D.E. and S. Ruff, eds., 280-282. Smithsonian Institution in association with the American Society of Mammologists, Washington DC.

Taylor, B.L., Baird, R., Barlow, J., Dawson, S.M., Ford, J., Mead, J.G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R.L. 2008. Grampus griseus. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.2. www.iucnredlist.org. Downloaded on 09 January 2012.