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Stenella longirostrisspinner dolphin

By Jennifer Bull

Geographic Range

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).

Habitat

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

Physical Description

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).

  • Range mass
    55 to 75 kg
    121.15 to 165.20 lb

Reproduction

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).

  • Breeding interval
    Adult females give birth to one calf every 2 or 3 years
  • Breeding season
    Spinner dolphins mate when their hormone levels are high, which is one or two times a year
  • Average number of offspring
    1
  • Average gestation period
    10.6 months
  • Range weaning age
    7 (low) months
  • Average weaning age
    7 months
  • Range age at sexual or reproductive maturity (female)
    5.5 to 10 years
  • Range age at sexual or reproductive maturity (male)
    10 to 12 years

Females nurse their calves for at least seven months.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

Behavior

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).

Communication and Perception

Food Habits

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).

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

Economic Importance for Humans

Economic Importance for Humans: Positive

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

Conservation Status

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).

Contributors

Jennifer Bull (author), University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

piscivore

an animal that mainly eats fish

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Klinowska, Margaret. 1991. Dolphins, Propoises, and Whales of the World: The IUCN Red Data Book. International Union for Conservation of Nature and Natural Resources, United Kingdom.

Norris, Kenneth S. 1991. Dolphin Days: The Life and Times of the Spinner Dolphin. W.W. Norton & Company, New York, London.

Norris, Kenneth S., Bernd Wursig, Randall S. Wells, and Melaney Wursig 1994. The Hawaiian Spinner Dolphin. University of California Press, Berkely, Los Angeles, London.

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