The spinner dolphin Stenella longirostris, is a small dolphin found throughout tropical waters around the world and belonging to the Delphinidae family of toothed whales. The spinner dolphin, as its name suggests, is known for its above-water displays of leaping and spinning several times, with up to 14 leaps in a row. Adults are typically 129–235 cm long and reach a body mass of 23–79 kg. Spinner dolphins generally have three-part colour patterns but tend to display geographic variation in form and coloration. Spinners have dark grey dorsal areas, light grey side areas and pale grey or white undersides, with a dark band bordered by a thin light line running from the eye to the flipper.
Spinner dolphins primarily live in coastal waters, islands, or banks and may occupy different habitats depending on the season. They feed mainly at night on small mid-water fish as well as squid, and shrimp. They are known to collaborate to catch their prey from a distance of 200 to 300 m, swimming around fish herd in circle and breaking through in pairs to make a catch. Spinner dolphins are preyed on by sharks, and possibly the killer whale, the false killer whale, the pygmy killer whale and the short-finned pilot whale.
Spinner dolphins live in open and loose social organizational structures. They are considered gregarious, occurring often in groups of several hundred to several thousand animals, and do not seem to mind travelling and feeding with other species such as bottlenose dolphins and humpback whales. They appear to have a promiscuous mating system, with individuals changing partners: multiple males may mate with one female in short, consecutive intervals. Mothers will nurse their calves for up to two years and will form strong social bonds with them. Maturity is reached at around seven years and calving occurs in intervals of up to seven years.
Spinner dolphins are highly communicative, using echolocation and special hearing to determine the size, movement and position of objects. They will also slap the surface of water to communicate with other dolphins about the presence of food, danger or if the group is changing locations.
The species is currently evaluated as “Data deficient”. Spinner dolphins are victims of bycatch throughout their range in purse-seine, gillnet, and trawl fisheries often in high numbers. They are the most abundant dolphin in the Indian Ocean and are caught throughout the region, with annual numbers of about more than thousands being reported in some of the few examined fisheries. Human use of by-catch has led to direct fishing in some regions.
Tourism development is also thought to affect the habitat and viability of spinner dolphins in some regions. Harassment of dolphins from dolphin-watching tours while they rest in shallow coastal waters during the day, potentially leads to changes in the behaviour and structure of the group.
Spinner dolphins are acrobats, they can jump out of the water front first and twist their body as they rise into the air, making two to 5.5 spins in one leap!