Risso's Dolphin

Risso's Dolphin Facts (Grampus griseus)

The Risso’s dolphin is one of the largest species out there. It is also one of the most distinct when it comes to their appearance. From a distance it may appear that a Risso’s dolphin has been involved in some type of battle. They have distinct markings on their bodies though that are different from each other.

The coloring ranges from various shades of gray. The distinctive markings on them are white. The darker that the color of the dolphin is the more apparent these types of markings are. These markings will likely be more apparent as they get older. They are the result of battles with each other and with their prey over the course of their lives.

Another unique feature is that they have seven sets of teeth on their lower jaw but none on the top. They feature one dorsal fin and two flukes. They range in length from 10 feet to about 12 ½ feet. Males can weigh up to 1,100 pounds with females weighing much less at about 650 pounds.

Distribution

These dolphins don’t come to the shore very often unless they are desperately searching for food. They prefer to remain out in the water and that makes it harder for people to see them. Some of the common locations where they have been noted include Monterey Bay, British Columbia, and the coast of California. It is estimated that there are close to 265,000 of them in the world.

They tend to have small migration patterns though that are still being learned about by researchers. Not all of them engage in it though and they don’t seem to go very far. It could be out of habit that they move because the water temperatures don’t drop enough for it to be a factor.

Behavior

Generally the Risso’s dolphins live in groups of about 30 but these groups may be much smaller. There have been documented observations of groups that have about 1,000 in them. Most of the members of the groups are females and it is speculated that that may remain in their group of origin their entire lives with the males moving in and out of various groups.

Diet /Feeding

Both squid and a variety of different types of fish are what these dolphins feed upon. They can consume very large quantities of them daily. They are fierce hunters due to their fast speed and sharp teeth. They tend to consume prey that is extremely large.

Reproduction

Reproduction for this species of dolphin occurs when they are about 9 feet in length. There isn’t much known about the reproduction process. It is believed that the mating season though is late summer. It takes about 14 months from conception before the pup will be born.

There have been documented cases of hybrids between the Risso’s dolphins and the bottlenose dolphins. These events have taken place both in the wild and in captivity. This shows that the two species are very compatible.

Conservation

Since the Risso’s dolphins aren’t in danger of extinction there aren’t any real conservation efforts in place to protect them. In parts of Japan and Taiwan they are killed and used for food. However, it isn’t believed that such practices are high enough in number to create a problem for their future.

Human interaction

Many Risso’s dolphins have been injured or killed due to being hit by boats that share the same areas that they do. Since they are curious animals they also can end up getting too close to these pieces of heavy equipment. Some people mistake this type of dolphin for a shark when it is in the water so they panic to get away. There aren’t known to attack humans.