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Spinner Dolphin |
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 ©FAO/FIGIS |
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Scientific name: Stenella longirostris longirostris
Pacific Island names:
nai`a (Hawaiian), mumua (Samoan)
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Stock Assessment / Estimated Breeding Population |
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The best available population estimate is approximately 3,300. Scientists are unclear whether these animals form a single breeding population or regularily move among island regions or between island waters or offshore areas. |
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Spinner dolphins are not listed as “threatened” or “endangered” under the Endangered Species Act (ESA), and although they are protected under the Marine Mammal Protection Act (MMPA), they are not considered "depleted" in the waters of the Pacific Islands Region. |
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Natural History |
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Spinner dolphins are probably the most frequently encountered cetacean in waters of the Pacific Islands Region. They get their common name from the impressive spins they perform during social encounters. Spinners spend their daylight hours in coastal waters, generally in calm bays. They use these areas to rest, care for their young and to avoid predators, before traveling to deeper water at night to hunt for food. Spinner dolphins have what is called a "fission-fusion society." They "fuse” to form large schools of hundreds of animals when feeding at night and split off into much smaller groups, sometimes of only a dozen individuals, when socializing and resting during the day. |
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Physical Description |
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- The spinner dolphin is a small dolphin that lives in open ocean and coastal waters.
- Individuals will generally grow from 4 to 7 feet in length and weigh between 100 and 165 pounds.
- Each has a long narrow beak, dark grey dorsal cape, medium grey flanks and a light grey/whitish belly.
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Diet |
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- Spinner dolphins feed at night on mesopelagic fish and squid that are found about 650-1,000 feet below the surface of the water.
Drawing: Spinner dolphins rest in shallow bays during the day
and feed in deeper waters at night. Dave Johnston/PIFSC
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Lifespan |
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- Lifespan is estimated to be about 20 years old.
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Reproduction |
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- Female gestation period is around 10 1/2 months and lactation lasts one to two years. The average interval between calves is three years.
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Distribution |
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- Spinner dolphins are found in the Atlantic, Indian and Pacific Oceans, generally found in tropical and subtropical regions. Stenella longirostris longirostris is a subspecies that resides in waters throughout NOAA's Pacific Islands Region.
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- Current research shows that pursuit and close approach of boats, swimmers and other ocean users to spinner dolphins may have negative impacts on their health and behavior.
- Other potential threats include entanglement in marine debris, anthropogenic (human made) noise, and fisheries interactions.
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Current Management Issues
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The Protected Resources Division is working on drafting an Environmental Impact Statement (EIS) on the potential rulemaking under the MMPA to provide more protection to Hawaiian spinner dolphins. The Notice of Intent (NOI) (Sept 2006, pdf 67kB) to prepare the EIS was published in the Federal Register on October 2, 2006.
For more information, please click here to visit our Spinner Dolphin - Human Interaction EIS and Rule-making page.
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- Remain at least 50 yards from spinner dolphins.
- Limit your time observing to 1/2 hour.
- Spinner dolphins should not be encircled or trapped between boats or shore.
- If approached by a spinner dolphin while on a boat, put the engine in neutral and allow the animal to pass. Boat movement should be from the rear of the animal.
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Important Phone Numbers |
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Marine Mammal Stranding/Entanglement Hotline: 1-888-256-9840 |
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More Information |
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