Grampus griséus, Cuvier, 1812

Identification

They have a robust body extensively scarred, a large rounded head, dark and prominent dorsal fin and long pointed flippers. The body tends to lighten with age and become almost white due to scars and scratches. Probably these scars are caused by the teeth of other dolphins of the same specie, and as they are unique, they allow the investigators to do the identification of these individuals. They have a frontal groove in the center of the forehead, running from the blowhole to the upper “lip”. At birth, the Risso’s Dolphin is uniformly gray and with age, changes to a very light gray.

Biology

The gestation period is 16 months and the calf is born with about 1.3-1.7m in length and is breastfed for 20 months. Adults can reach 3.8m in length. Females reach sexual maturity at age 6, while males reach sexual maturity at age 12. The weight of an adult varies between 300 and 500kgs. They feed on crustaceans and cephalopods, preferring squid.They have a wide distribution, but prefer deep waters, despite being seen near the coast. Longevity in this species reaches 40 years.

Behavior

Young animals jump and older animals tend to do a half-breach, hitting the side of the head onto the surface. Sometimes they raise their heads to “spyhopping”, with their flippers exposed. It is rare to “Bow-Riding”. It is typical to dive for 1 to 2 minutes, but can stay under water for up to 30 minutes. When hunting, groups sometimes spread out in a long line. Some are very shy and others allow a close appoach.