Grampus griseus

The gray dolphin is called Risso's dolphin in English, and has no subspecies.

The gray dolphin has the habit of swimming in the ocean. Usually there are groups of 10 to dozens of heads, and there are also large groups of hundreds of heads, and sometimes mixed with other types of dolphins. Gray dolphins prefer waters with a depth of more than 180 meters and a water temperature above 10℃, but sometimes they also go to waters with a water temperature of 5-6℃. They do not gather in large groups, and the groups are all less than a few to 20. When they are in a group, their swimming speed is not too fast, but when they are fighting, their swimming speed is very fast, and the instantaneous speed is estimated to be more than 20 nautical miles. When playing, they often expose half or all of their bodies above the water surface, splashing high waves, and sometimes they use their tail fins to hit the water while circling. Trained gray dolphins can also perform some difficult movements according to commands, such as heading the ball, jumping, moving the bell, and drilling hoops.

Gray dolphins mainly forage in the mixed area of nearshore and offshore, especially in the water layer between 600-800 meters, and often follow prey into the shallow waters along the continental shelf. Their diet includes small squid, fish, krill, crustaceans and cephalopods, and the main food is large argonauts.

Most female dolphins reach sexual maturity at 8-10 years old, and male dolphins reach sexual maturity at 2.6-2.8 years old. However, compared with age, body size is still the main indicator of sexual maturity in marine cetaceans. The gestation period lasts 13-14 months, and the average weight of newborn dolphins is 20 kg. They are weaned 12-18 months after birth. They can reproduce all year round, and the peak birthing season in the North Atlantic and Eastern Pacific is in summer and winter respectively.

The calves are mainly cared for by female dolphins. As for paternal behavior, it is extremely rare among cetaceans and has not been recorded in gray dolphins. Newborn dolphins are precocious and can swim immediately after birth. The calves live in a "pod" group consisting of mothers and children until they leave a few years before sexual maturity. Alloparental care has also been found among gray dolphins. Usually, when the mother of a calf goes out to forage, another female dolphin will help take care of it.

There is no statistics on the number of gray dolphins in the world. The situation in various places is as follows: As of 1999, there were an estimated 950 in the eastern Sulu Sea. In 1999, the estimated number in the coastal waters of Sri Lanka was 5,500-13,000. According to the survey data in 2008, there were 83,300 in three concentrated coastal waters in Japan. As of 2006, there are about 16,066 subpopulations in California, Oregon and Washington; 2,351 in the waters around Hawaii; about 20,479 gray dolphins living in the eastern United States; and 2,169 in the northern Gulf of Mexico. Wade's 1993 statistics show that there are 175,000 in the eastern tropical Pacific.

Listed in the "China Species Red List": Endangered (EN).

The populations in the Mediterranean, North Sea and Baltic Sea are listed in Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS).

Listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

Listed in the 2012 Red List of Endangered Species of the World Conservation Union (IUCN) ver 3.1 - Least Concern (LC).

Listed in the second level of the "List of National Key Protected Wildlife in China".

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Gray dolphins are widely distributed, mainly living in deep waters of the continental slope and outer continental shelf (especially the steep seabed terrain), as well as the temperate waters of the northern and southern hemispheres that pass through the tropics.
Main distribution countries and regions (sea areas): Algeria, Angola, Anguilla, Antigua and Barbuda, Argentina, Aruba, Australia, Bahamas, Barbados, Bermuda, Brazil, Canada, Chile, Cayman Islands, China, Colombia, Comoros, Cook Islands, Costa Rica, Cote d'Ivoire, Croatia, Cuba, Curacao, Denmark, Dominica, Ecuador, France, French Polynesia, French Southern Territories, Gabon, Gambia, Germany, Ghana, Gibraltar, Greece, Grenada, Guadeloupe, Guam, Guatemala, Guernsey, Guinea Bissau, Haiti, India, Indonesia, Iran, Ireland, Israel, Italy, Jamaica, Japan, South Korea, Lebanon, Madagascar, Maldives, Malta, Mauritius, Mayotte, Mexico, Morocco, New Caledonia, New Zealand, Oman, Panama, Papua New Guinea, Peru, Philippines, Russia,

The gray dolphin has a spindle-shaped body, 250 cm long and weighs 164 kg. The front part of the dorsal fin is thicker and becomes very thin from the anus to the back. The head is blunt and round, without bulges, and there is a triangular depression in the front midline. There is no snout. The mouth is located in the front and lower part of the head, with a large mouth cleft that is tilted upward and backward, and the front end of the upper jaw slightly protrudes from the front end of the lower jaw. The eyes are small and located obliquely above the corners of the mouth on both sides of the head. The external ear holes are extremely small and located behind the eyes. The breathing hole (external nostril) is a half-moon-shaped crack that bends forward and is located in the middle of the top of the head. The dorsal fin is narrow and high, with a pointed end and a sickle-shaped concave rear edge. Its height is 8.5% of the body length, the upper end is pointed, and the rear edge is concave