Common Name: Risso’s Dolphin
General Description: Risso’s dolphins have a body that is deep and massive for the front two thirds, and then tapers behind the dorsal fin to a narrow tail stock. There is a very small beak, and the head is large. The slight melon is marked by a crease that may be observed only from close quarters.
The long, pointed flippers are broad based. The tall, slender dorsal fin is very prominent.
They are dark to light grey above, older individuals being paler. The head is sometimes completely white, with a dark area around each eye. The dorsal fin and an area of the back adjacent to its base, the flippers and flukes remain dark. Extensive white scarring covers the body of adult animals, making them readily recognisable. The scars seem to be the rake marks made by the teeth of mates or rivals. There is an oval or anchor-shaped white patch on the chest and chin
Size: Adults: Risso’s dolphins may attain lengths of 3.8 m. Females are a little shorter than males. The weight is 400 to 500 kg, even 680 kg. Calves at birth, 1.5 m long.
Appearance At Sea: Risso’s dolphins usually travel in groups of 12 to 50, but may be seen solitary or in herds of several hundreds. These are active dolphins, spyhopping, breaching and slapping their tail flukes.
Found In: These are deep-water animals. However, herds may be seen in depths as low as 100 m. They feed mainly on squid.
Records from India: Risso’s dolphins have been observed close to the shelf slope off peninsular India and both Lakshadweep and Andaman Nicobar islands.
World Distribution: Found in most tropical and warm temperate oceans and seas with a temperature of 15° – 25° C. It avoids polar seas.
Could Be Confused With: At a distance, there is a possibility of confusion with bottlenose dolphins and False Killer Whales.
Diagnostic Features:At sea, prominent dorsal fin, extensive scarring, lack of beak.
Stranded Specimens: A freshly beached Risso’s Dolphin can be recognized by the scarring and the groove on its forehead. Normally there are no teeth in the upper jaw and only a few in the lower jaw. These teeth are strong and oval, and located at the front of the jaw. They may number 2 to 7 in each row. This dentition configuration is unique among cetaceans.