Risso’s dolphin is part of the cetacean family and can be found swimming in most of the worlds major oceans, however they typically prefer living in warm tropical climates in waters that exceed 1,300 ft (400 meters).
As with all other species of dolphin Risso’s dolphin is a marine mammal and belongs to the toothed whale suborder.
These dolphins are solitary animals and are easily distinguished by their near black to light gray colored skin tone and bulbous shaped head.
Physical Characteristics and Appearance
These dolphins generally grow to be around 9 – 11 ft in length and weigh between 600 – 1100 pounds, however some dolphins may grow to be as large as 14 ft with the female dolphins growing to be slightly larger than their male counterparts.
At birth their skin takes on a dark grayish-brown tone with a white colored under-body and sides around the pectoral fins and mouth.
As they age however their skin goes from a dark near black coloring to a light gray color.
They also have a blunt bulbous shaped head and a large dorsal fin which helps them stabilize and navigate through the ocean water.
Diet and Hunting Methods
The typical diet for risso’s dolphin consists of a variety of fish, krill and cephalopods such as squid, octopus and cuttlefish, however they tend to prefer consuming squid over most other forms of food.
Most hunting takes place during the evening and at night when their prey moves closer to the surface of the water and while Risso’s dolphin tends to make short dives (lasting less than 5 minutes ) when hunting for food they can dive to depths in excess of 1,000 ft and hold their breath for up to 30 minutes if they need to.
Social Structure and Communication
Risso’s dolphin is a largely solitary marine animal that can often be found traveling in small groups of 5 or more dolphins, however during certain social events they can be seen traveling in pods consisting of 50 to several hundred dolphins and may even be seen intermingling with other marine mammals such as bottlenose dolphins and gray whales.
These dolphins communicate through a series of clicks and whistles which allow them to communicate a number of different things to one another such as to alert others of nearby danger, to communicate that they have found food, to communicate a desire or need and to socialize with one another.
In order to identify one another each dolphin has a unique frequency that allows the group to know which one is communicating in the group.
This can be especially useful in large pods where one dolphin can easily get lost in the group.
Migration
Unfortunately not much is known about the migration patterns of these dolphins, however in some locations these dolphins have been seen migrating between on and offshore areas and it is believed that dolphins in some areas may make small migrations in order to maintain their food supply, especially in colder regions where fish and squid may relocate to warmer climates during the cold winter months.
In areas such as California there has been no known significant migration patterns discovered.
Mating, Reproduction and Lifespan
The average gestation period for Risso’s dolphin is estimated to be 13 – 14 months.
These dolphins have been known to produce a single offspring once every 2 – 3 years on average while they are fertile.
Depending on where the dolphins are located their primary mating periods may occur in the summer, fall or winter.
Risso’s dolphin reaches sexual maturity between the ages of 8 – 12 with females typically maturing 2 years before their male counterparts.
It is estimated that the average lifespan for these dolphins range from 20 – 30 years with some dolphins reaching nearly 35 years of age.
Habitat
Risso’s dolphins can be found swimming in most of the worlds major oceans, however they typically prefer living in warmer tropical climates in deep offshore waters.
They can been found swimming in the Atlantic, Indian and Pacific oceans and their distribution range spreads from the Gulf of Alaska to Tierra del Fuego.
In terms of environment these dolphins generally enjoy climates between 50 – 70 °F (10 – 21 °C) in waters that exceed 1,300 ft (400 meters) of depth.
Threats and Predators
Risso’s dolphin is assumed to have an abundant population however they do face some human threats.
Some of the threats these dolphins face include getting caught in fishing nets, collisions caused by boats and other man-made transportation, water pollution and poachers that hunt them for their meat.
Endangered level
Risso’s dolphin is not currently considered endangered.