(Grampus griseus)
Introduction
If you are interested in seeing a more uniquely appearing dolphin, here is one for you to check out. The Risso's Dolphin is very different in appearance than most of the other species. This is one of the few dolphin species where the males and females are almost going to be identical in size instead of the males being larger.
Description
The square design of the head is one of the telling signs of the Risso's Dolphin. They have a long dorsal fin as well as flippers that are recurved and pointed but also elongated. The body is stocky but it tapers as it moves from the front to the back of the body. They can be from 8 ½ to 13 feet long. They can also weigh as much as 880 pounds.
You will find this dolphin out there in a variety of colors. When the young are born, they are gray or brown in color with white areas. They may have yellow around the muzzle and white around the flippers. As the calves get older, they start to turn silver in color and then to a dark black color. They may keep their patches of white though as they mature. However, as they get to the age of maturity, they will get lighter around the flanks, abdominal area, and the head.
These dolphins feature teeth in the upper jaw that are pointed. In the lower jaw though they will have from 2 to 7 pairs of peg like teeth. This helps them with getting their prey, when they need to fight off predators, or when they are competing for mates or other resources.
Distribution
The Risso's Dolphin is found around the world in the warm tropical waters. They tend to spend most of their time in the deeper waters so it isn't often you will see them close to the shore. In addition to all of the oceans, they are also found around the Red Sea, Mediterranean Sea, and the Persian Gulf. It is a myth though that they live in the Black Sea. There has never been a confirmed sighting of them in that body of water.
They tend to enjoy deeper water that ranges from 1,300 feet to 3,300 feet. They tend to enjoy water that is from 59 degrees Fahrenheit to 68 degrees Fahrenheit.
Behavior
Even though these dolphins tend to stay away from boats in the water, they are known to surf bow waves. Since they don't come to shore often, there is little really known about the overall behaviors of the Risso's Dolphins. They are known to be very social though just like other species of dolphins.
They often form pods with 10 to 50 members and they can create very deep bonds with each other. The average is about 30 members but during migration for feeding there are times when more than 4,000 of them are in one location. Then they have many subgroups that they are divided into. They are also known to interact with other species of dolphins.
Interesting information about Risso's dolphin
Risso's dolphin in azores islands
Feeding
Squid is the majority of food for this species of dolphin. They will eat a variety of fish as well. They will feed mainly at night though as that is when the squid will be moving towards the surface of the water. They have been seen consuming cephalopods, krill, and crustaceans too. They spend about 77% of their time traveling but only about 5% of that time is actually for feeding. They can dive up to 1,000 feet for food, and remain under the water for up to ½ hour before they need to surface for air.
Reproduction
It is believed that the social structure of these dolphins plays a huge role in the larger pods. There can be entire pods of females so males will be attracted to them for mating purposes. Hybrids in the wild and captivity with Bottlenose Dolphins have been documented. The females are from 8 to 10 years old when they mate and for males it is from 10 to 12 years.
After mating, the young calf will be born from 10 to 12 months later. The time of year for mating depends on the region where the Risso's Dolphins live. The young will remain with their mother in her pod until a year or two before they are ready to start mating on their own.
Conservation Status and Threats
There are an estimated 310,000 Risso's Dolphins around the world, but it can be tough to get an exact count of them. They are one of the few species out there that seems to have high enough numbers to not need lots of conservation efforts. They don't seem to be widely hunted and they do well in captivity. One of the risks to them though is pollution to their natural habitat. Issues with noise pollution in some locations can also create high levels of stress for them.
