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 Wilson's Storm-petrel  Dave Jones

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Dolphins & Porpoises




Risso's Dolphin

Grampus griseus






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Risso's Dolphin Scott Spangenberg

Risso Dolphin mother and calf photographed on June 2010 BBC offshore pelagic. by Scott Spangenberg..The unscarred skin of the calf on right is dark.

Risso's Dolphin
Also commonly referred to by the genius Latin name "Grampus". Risso's Dolphin can be seen on offshore trips on the east and west coast.

Identification
The Risso's Dolphin has a beakless head and a tall falcate dorsal fin that is centrally located on the back. In a close view, you can observe a diagnostic crease in the forehead between the two eyes

The belly is white and the back gray. The body lightens with age and is often highly scarred by straight lines probably made by the teeth of other Risso’s Dolphins. In adults the scarring may conceal the distinct border between the white belly and gray back. All have light gray or white marking on the undersides.  These typically consist of an anchor-shaped chest patch, connected by a light streak to a large, diffuse zone of white between the umbilicus and the anus. (Folkens 2002).Flippers are sickle shaped..

 
This breeching Risso's Dolphin shows the anchor-shaped chest patch.  You can also see this pattern in photo below of the young dolphin that washed up dead on the Parker River beach.

It is very unusual for this pattern to show up as well on an adult animal as usually the animals sports many white scars.
This pattern is also seen on Pilot Whales.

Unfortunately I have no reference to where this photo was taken or by whom.   

Behavior
Travels in pods of 12 to 40 individuals.  Loose aggregations of 100-200, or even several thousand, are seen occasionally.  (Folkens 2002).

Breeches (leaps from the water). Spy hops ( pushes head above the water). Seldom rides the bow wave of a moving boat.

Feeding
Primary food is squid and Risso’s usually feeds at night when the prey migrates to the surface. May take other cephalopods such as octopus and cuttlefish. ( Folkens 2002).

Range
Risso’s Dolphin is found in tropical and warm temperate waters of all oceans and large seas ( Mediterranean, Red). In some seasons occupies a niche descibed as the steep upper continental slopes, where water depths usually exceed 1000 feet. (Folkens 2002). This is probably why we see this dolphin on long pelagic trips to the canyons on the continental shelf south of Cape Cod.

 
Risso's Dolphin Glen Tepke California

This picture taken by Glenn Tepke off the coast of California shows the beakless head and scarring of the body of one individual and the tall dark dorsal fin of another.

Notice the lack of a beak and the sickle-shaped flippers. The upper jaw slightly overlaps the lower jaw.


This behavior is called “spy hopping”.


Risso's Dolphin David Jones

Breeching Risso's Dolphin photographed by David Jones. Notice the tall falcate dorsal fin, the shape of the flippers, and the scarred gray skin..

Two  Risso's Dolphins  Scott Spangenberg

Two Risso’ Dolphins photographed by Scott Spangenberg. Notice the tall falcate dorsal fin and the scarred gray skin of the mother on the right..

Dead Risso's Dolphin Found on Beach at the Parker River National Wildlife Refuge Dec 2015

A visitor to the refuge headquarters on Dec 21, 2015 reported that he had seen a dead "porpoise" on the beach.  He was very vague about where it was located.  A ranger went down the beach and took a photograph of the animal.  Eventually Tom French retrieved the specimin.  He said that the animal was a newborn Risso's Dolphin.  Notice the hour glass pattern on the underside which is like that on the pilot whale.  This led to several knowledgeable people calling this a pilot whale.     Photo Jean Adams Tom French prepared the skeleton for the museum at Harvard.

Risso's Dolphin

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Comments to webmaster
Folkens, Peter (2002) Guide to Marine Mammals of the World Alfred A. Knopf New York

Kinze, Carl Charistian (2001) Marine Mammals of the North Atlantic Princeton University Press Princeton NJ