Stenella longirostris
spinner dolphin

Spinner dolphins are found in the tropical and subtropical waters in the Atlantic, Indian and Pacific oceans. They can also be found in some warm temperate areas. Spinner dolphins often occur near islands (Klinowska 1991).

Stenella longirostris is mostly pelagic. It does spend time in both shallow waters and deeper water farther from land.

Spinner dolphins are six to seven feet long and have a three part color pattern on their bodies. The pattern consists of a dark gray back, a pearl-gray side panel, and a white belly. Males possess a postanal hump and are generally larger than the females (Norris, 1991). Spinner dolphins that live farther away from land are morphologically different from those that live close to land (Norris et al, 1994).

Spinner dolphins are polygynandrous. The male senses when the female is ready to mate and pursues her. Mating happens within the school with no real mate selection.

Spinner dolphins mate when their hormone levels are high, which is one or two times a year. The male swims upside down underneath the female and inserts his penis into the female's reproductive tract (Norris, 1991). Males reach sexual maturity at about 10-12 years old, while the females' age at sexual maturity ranges from 5.5-10 years old. Adult females give live birth to one calf every 2 or 3 years. Gestation period averages 10.6 months (Klinowska, 1991).

Females nurse their calves for at least seven months.

Spinner dolphins may occur in schools with as many as 1,000 individuals, but it is common to have 200 or fewer to a school. They are very social with each other and with other species of ocean dwellers. Spinner dolphins have been known to associate with spotted dolphins, yellowfin, and skipjack tuna (Klinowska, 1991). Spinner dolphins rest in shallow waters, usually inlets. They tend to go back to the same area each day. When they are done resting, they quickly swim out to the deep area to feed on the vertically migrating fauna. When they are in the deep, darker waters, they are more susceptible to predation. There is a dominance hierarchy within the schools of spinner dolphins. It is sustained by a descending order of threats and by behaviors that involve caresses. Threats are usually a simple nudge or abrupt gesture. These hierarchies are active when the school is in an enclosed area, and not in the open sea (Norris, 1991).

Spinner dolphins communicate with each other by echolocation, caressing each other, and using aerial patterns. They are most active when they have just finished resting. Stenella longirostris performs many kinds of jumps. The spinning jump is the trademark jump for this species; they are named for their amazing aerial spinning maneuvers. They do this most frequently at night (Norris et al., 1994).

Spinner dolphins are carnivorous. They eat mesopelagic fish and epipelagic and mesopelagic squid and shrimp (Klinowska, 1991). Most of the prey they eat are vertically migrating species (Norris et al., 1994).

Spinner dolphins attract tourists for dolphin watching. They are also subject to scientific investigation because of their remarkable capacity to learn.

The major threat to spinner dolphins is getting caught in tuna nets. There is also habitat destruction in some areas due to tourism. Spinner dolphins are protected in some countries. In the United States, special efforts have been made to monitor and reduce deaths due the tuna industry (Klinowska, 1991).