![]() Population numberĪccording to IUCN, the Risso’s dolphin is locally common and widespread throughout its range but no overall population estimate is available. Other notable threats to the population of this species include anthropogenic sounds, usually produced by navy sonar or seismic exploration: these sounds, which resonate through the ocean, are extremely dangerous for dolphins, causing gas-bubble disease, which, in turn, leads to high number of mortality among this species. In some parts of its range, this dolphin is often incidentally caught in fishing gears. The animal also suffers from overfishing particularly in Japan, where Risso's dolphin is fished for its meat. Presently, one of the potential concerns to the global population of Risso's dolphin is climate change, since rising ocean level and increasing temperature of the water's surface may lead to decline as well as changes in distribution of its prey species. Calves are weaned within 12 - 18 months after birth, gaining their sexual maturity at a length of 8.5-9 feet or 2.6-2.8 meters. ![]() Young dolphins live in these groups until they become sexually mature. Within these pods, it is common to care for another female's calf, while its mother is foraging for food. Females and their young usually gather into separate groups, where mother dolphins help each other raise calves. Soon after the birth, the calf is ready to swim. Gestaiton period lasts for 13 - 14 months, yielding a single baby, which is born precocial. Considering the global distribution of Risso's dolphins, these animals are likely to mate and give birth at any time of year, though populations off South Africa most frequently breed in December-April. Thus, females of Risso's dolphin are known to form single-sex groups, which attract mating males. However, reproduction is affected the by social structure of this species. Little is known about the mating behavior and system of this animal. Risso's dolphins interact with each other, using different forms of communication such as breaching, chasing, biting, leaping out of the water and lob-tailing. The animals are also known for their aggressive physical contacts, including flipper slapping between conspecifics, striking with flukes and dorsal fins as well as body blows. Males of this species can often be seen bothering False killer whales, Bottlenose dolphins and other animals. Risso's dolphins are night feeders, since cephalopods, which are the main prey species of these animals, come to the water's surface during the nighttime hours. The species have been observed mixing with other cetaceans to form foraging groups. Their groups often include individuals of the same age and sex. However, Risso's dolphins are also known to gather in very large groups of up to 4,000 dolphins, when there is enough food. The material on this site is NOT permitted to be used on other websites or for comercial use without written permisson from Rob Harrison.These highly social animals usually form groups, varying from 10 to 50 individuals with an average of 30. Please feel free to use the pictures as your desktop background, in school projects, or give them to friends, as long as they are unmodified. You may use the pictures and content from this page for school and personal use ONLY. The Dolphin Picture Page has been accessed times since Oct 2001Īll written articles, pictures, and movies contained in this page are © Rob Harrison, unless otherwise noted. Movies | Dolphins | Killer Whales | Belugas You may use these pictures for personal or school use, but please contact me about other uses. The lower pictures are of White Wings, a Pacific White-sided dolphin at the Vancouver Aquarium Marine Science Centre, except for the top left picture, which was taken at Sea Life Park in Hawaii of the world's only half false killer whale, half bottlenosed dolphin.Ĭlick on any of the images below to see a bigger version The pictures here are grouped according to the dolphin in the picture, starting in the order I just stated. Many of the pictures here are from my trip to The Dolphin Institute (Kewalo Basin Marine Mammal Lab), and include pics of my four favorite dolphins in the whole wide world.
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