Protected Resources

Spinner Dolphin


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

Current Management Issues

On August 23, 2016, NOAA Fisheries published a proposed rule to enhance protections for Hawaiian spinner dolphins to prevent disturbance and harassment from dolphin-directed human activities. The proposed rule would prohibit swimming with and approaching a Hawaiian spinner dolphin within 50 yards by any means (vessel, person, or other object) and would be implemented within two nautical miles from shore of the Main Hawaiian Islands and in designated waters between Maui, Lanai, and Kahoolawe where spinner dolphins are found throughout the day.

Resident populations of Hawaiian spinner dolphins feed offshore throughout the night and return to Hawaii's coasts to rest during the day. Because Hawaiian spinner dolphins rest in Hawaii's sheltered bays and along its coastlines and are one of the most easily encountered cetaceans in the waters of the Main Hawaiian Islands, they are vulnerable to disturbance and harassment. Dolphin-directed activities have grown dramatically in recent years, and the easily accessible Hawaiian spinner dolphins face heavy and increasing pressures from people seeking a dolphin experience. Chronic disturbance to resting activities can negatively affect the health and fitness of dolphins.

The proposed rule is based on the preferred alternative (Alternative 3A) in the Draft Environmental Impact Statement. Other alternatives considered include the following:

Key Documents:

Can I Still Submit Comments?

The public comment period is closed.

For more information about Spinner dolphins and the proposed rule, please visit:
Spinner Dolphin - Human Interaction EIS and Rule-making page.

Stock Assessment / Estimated Breeding Population

Hawaii has 5 distinct island-associated stocks of Hawaiian spinner dolphins. The stocks are as follows: 1) Midway/Kure, 2) Pearl and Hermes Reef, 3) Kauai and Niihau, 4) Oahu/4-islands (including Maui, Lanai, Molokai, Kahoolawe), and 5) Hawaii Island. These stocks live in coastal waters ranging to 10 nautical miles from the shore of their resident islands. All other spinner dolphins found outside of 10 nautical miles and within the U.S. Exclusive Economic Zone (including those at French Frigate Shoals) are part of the Pelagic stock. These stocks are reproductively isolated populations, meaning that there is little to no breeding occurring between stocks (Andrews, 2009).

A robust estimate for population size is only available for the Hawaii Island stock, which is estimated to be around 600 animals. The Kauai/Niihau stock is estimated to be around 500 animals and Oahu/4-Islands stock is estimated to be around 300 animals; however, both of these estimates lack data from the stocks' full range. Information is insufficient to provide estimates for the other three stocks.
For species-specific stock assessment information, please see here.

Legal Protection

All marine mammals are protected from "take" under the MMPA. The MMPA defines take to mean "to harass, capture, or kill" any marine mammal or attempt to do so. Harassment is further defined by the MMPA as any act of pursuit, torment, or annoyance that has the potential to do the following:

When viewing spinner dolphins in the wild, people must ensure their activities will not result in "take." For responsible viewing guidelines provided by NOAA Fisheries, please see here.

Natural History

An illustration of Spinner dolphins resting in shallow bays during the day and feeding in deeper waters at night. NOAA Fisheries/Dave Johnston

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

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




Potential Threats

Viewing Guidelines

Important Phone Numbers

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

More Information