Protected Resources

Spinner Dolphin


Scientific name: Stenella longirostris longirostris
Pacific Island names: nai'a (Hawaiian), mumua (Samoan)

Stock Assessment / Estimated Breeding Population

The best available population estimate is approximately 3,300. Scientists have proposed 6 separate stocks for the Hawaiian Islands. Two distinct stocks in the Northwestern Hawaiian Islands: Kure and Midway atoll; Pearl and Hermes Reef; and three in the Main Hawaiian Islands: Niihau/Kauai; Oahu, Maui, Lanai, Molokai, Kahoolawe; and the Island of Hawaii. The sixth stock includes all other animals within the EEZ, including those at French Frigate Shoals. These stocks are reproductively isolated populations, with few or no genetic exchange occurring (Andrews, 2009).

Legal Protection

All marine mammals are protected from "take" under the Marine Mammal Protection Act (MMPA). The MMPA states that the essential habitats used by marine mammals should be protected, and marine mammals should be protected from the harmful actions of man. Responsible viewing guidelines provided by NMFS can be found at Spinner dolphins are currently not listed as "threatened" or "endangered" under the Endangered Species Act (ESA).

Natural History

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 social pattern." 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.

Physical Description


Drawing: Spinner dolphins rest in shallow bays during the day and feed in
deeper waters at night. Dave Johnston/PIFSC




Potential Threats

Current Management Issues

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.

To learn more about the potential impact of swimming with wild spinner dolphins, please visit our webpage entitled "Swimming with Wild Spinner Dolphins"

Viewing Guidelines

  • 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.

Important Phone Numbers

Marine Mammal Stranding/Entanglement Hotline: 1-888-256-9840

More Information