Where are they located?
The Risso's dolphin (Grampus griseus) has a very wide distribution. It lives in temperate, subtropical, and tropical waters of the oceans in both hemispheres.
The seasonal migrations of Risso's dolphins are not clear. It appears that they remain in most of their geographical range year-round. Residents of northern areas usually migrate seasonally. For example, populations that are off the northern coast of Scotland in summer move towards the Mediterranean during winter, and populations off the coast of California migrate to Mexican waters in winter.
What is its habitat?
The Risso's dolphin inhabits oceanic and continental waters, at depths of between 400 and 1,000 m. They can often be seen offshore near continental slopes and shelves, or next to seamounts or submarine canyons. Their preference for this habitat could be explained by the high marine productivity of these areas, which provides them with abundant feeding opportunities.
The waters in which the Grampus griseus is most commonly found have temperatures between 15° and 20° C, and rarely fall below 10° C.
Are they endangered?
Risso's dolphin is distributed worldwide and is relatively abundant. However, little is known about this species. Details of its location are often lacking, and only estimates have been made in some regions.
Grampus griseus is threatened by overfishing in some areas where it lives. In Sri Lanka, some 1,300 individuals are caught annually for human consumption and fish bait. In Japan, Risso's dolphin is also fished for meat and fertilizer. Between 250 and 500 specimens are killed in the annual drive fishery. Direct killing also occurs in the Caribbean, Indonesia, and the Philippines.
Occasionally, this species is also caught as bycatch. Cases have been reported in the North Atlantic, the Mediterranean Sea, the Southern Caribbean, the Azores, Peru, the Solomon Islands, and the North American coast. However, a small number have also been caught for live display in aquariums.
As Risso's dolphin is a deep diver that feeds on squid and relies on echolocation to hunt, it is at risk of vulnerability due to noise pollution caused by naval sonar and seismic exploration.
The increasing amount of plastics and other waste in the sea can also pose a threat to populations of small cetaceans. The predicted impacts of climate change on the marine environment may also affect this species, although the potential consequences are not clear.
Due to the high levels of pollution accumulated in the tissues of small cetaceans, the consumption of their meat can be harmful not only to children and pregnant women, but also to the general population.
Assessed as Least Concern by the IUCN Red List of Threatened Species (2012).
