Risso'S Dolphin

Risso's dolphin has a relatively large anterior body and dorsal fin, while the posterior tapers to a relatively narrow tail. The bulbous shape of the head has a vertical crease in front.

Risso's dolphins are found nearly worldwide, from cold and temperate to tropical waters, in the Indian, Pacific and Atlantic Oceans, as well as parts of the Baltic Sea, the Persian Gulf, and the Mediterranean, North, and Red Seas (excepting the Black Sea; however, a rare stranding was recorded in the Sea of Marmara in 2012).). Several sightings have been documented in Roskilde Fjord, in the waters of Lejre Vig, just off of the coast of Skjoldungernes Land National Park, Denmark. Analysis of Risso's dolphins found in the UK and the Mediterranean display variations in mitochondrial DNA. One possible reason for these differences could be the lack of interaction between individuals in the two locations.

They feed almost exclusively on neritic and oceanic squid, mostly nocturnally. Predation does not appear significant. Mass strandings are infrequent. Analysis carried out on the stomach contents of stranded specimens in Scotland showed that the most important species preyed on in Scottish waters is the curled octopus (Eledone cirrhosa).

A population is found off Santa Catalina Island, where they are sympatric with short-finned pilot whales (Globicephala macrorhynchus), and both species feed on the squid population. Although these species have not been seen to interact with each other, they take advantage of the commercial squid fishing that takes place at night. They have been seen by fishermen to feed around their boats. They also travel with other cetaceans. They surf the bow waves of gray whales, as well as ocean swells.

Gestation requires an estimated 13–14 months, at intervals of 2.4 years. Calving reaches seasonal peaks in the winter in the eastern Pacific and in the summer and fall in the western Pacific. Females mature sexually at ages 8–10, and males at age 10–12. The oldest specimen reached 39.6 years.

Risso's dolphins have successfully been taken into captivity in Japan and the United States, although not with the regularity of bottlenose dolphins or orcas.

Recent studies have shown a possibility of hybridization occurrences between Risso's dolphins and bottlenose dolphins. So far, possible hybrid individuals have been documented in United Kingdom waters. Hybridization is not uncommon with cetaceans, so these hybrids likely do not have any evolutionary advantage, but instead are more likely an uncommon chance event.

Like other dolphins and marine animals, these dolphins getting caught in seine nets and gillnets have been documented across the globe. Many of these incidents have resulted in death. Small whaling operations have also been cause of some of these deaths. Pollution has also affected many individuals that have ingested plastic. Samples from these animals show contamination within their tissues.