Spinner dolphins are small, slim dolphins named for their spectacular spinning leaps. Adults are 1.3-2.4 meters (4-8 feet) long and weigh 23-80 kg (50-175 lbs). They have a long, thin beak and a tall dorsal fin, and most are coloured in three bands: a dark grey back, lighter grey sides and a white or pink belly.
There are four subspecies, and they look surprisingly different. Gray's spinner, the most widespread, has the classic three-tone pattern, while the eastern spinner of the eastern Pacific is almost uniformly grey, with a dorsal fin that leans forward in adult males.
Spinner dolphins live around 20-25 years. Females have a single calf every three years after a pregnancy of about 10 months.
Spinner dolphins live in tropical and subtropical oceans around the world, mostly in deep water far from shore. Around islands such as Hawaii, however, they follow a daily routine: resting in calm, shallow sandy bays during the day, then moving offshore at dusk to feed.
Because those resting bays are also popular with swimmers and tour boats, Hawaii now restricts how close people may approach them.
Spinner dolphins feed at night on small fish, squid and shrimp that rise from the deep scattering layer, a band of sea life that migrates toward the surface after dark. Their main prey are lanternfish only a few centimetres long.
They dive to 200-300 meters (650-1,000 feet) and hunt cooperatively, with groups spreading out and then closing in to concentrate their prey.
A spinner dolphin can leap high into the air and spin on its long axis up to seven times before splashing down. Scientists think the spins may knock off clinging remora fish, send signals to the rest of the group, or simply be play.
They live in groups ranging from a few dozen to several thousand, with membership shifting from day to day. In the open Pacific they often swim with pantropical spotted dolphins and schools of yellowfin tuna.
Stenella longirostris is one of five species in the genus Stenella, all slender tropical dolphins in the family Delphinidae. The species name means "long-beaked".
The IUCN lists the spinner dolphin as Least Concern. The eastern spinner subspecies, however, lost more than half its numbers between the 1960s and 1980s when hundreds of thousands drowned in tuna purse-seine nets in the eastern Pacific, and it has been slow to recover despite dolphin-safe fishing rules.
Other threats include disturbance of resting bays by tourism, entanglement in fishing gear, and hunting in some parts of the world.
