- Proposed rule for protective regulations for Hawaiian spinner dolphins.
- Advance notice of proposed rulemaking.
- Notice of intent to prepare an environmental impact statement.
About the Species
Spinner dolphins are probably the most frequently encountered cetacean in nearshore waters of the Pacific Islands Region. Spinner dolphins received their common name because they are often seen leaping and spinning out of the water. The species' name, longirostris, is Latin for “long beak,” referring to their slender shaped beak or rostrum.
Regarded as one of the most acrobatic of dolphins, spinner dolphins are well known for their habit of leaping from the water and spinning up to seven times in the air before falling back into the water. Experts believe that spinner dolphins use these behaviors primarily for acoustic signaling or communication, but the activity can also be a way to remove ectoparasites, such as remoras.
CITES Appendix II
- Throughout Its Range
- Throughout Its Range
- Eastern stock
Spinner dolphins are relatively small compared with other species of oceanic dolphins. They are slender, with thin, recurved flippers, and dorsal fins that usually range from slightly curved to erect and triangular. Among Gray’s spinner dolphins (the subspecies that includes Hawaiian spinner dolphins), adult females are 4.6 to 6.7 feet long and adult males are 5.2 to 6.8 feet long. They reach weights of at least 181 pounds. There is a great deal of color variation in spinner dolphins across the globe, depending on the region and subspecies of dolphin. Gray’s spinner dolphins exhibit a tripartite color pattern with counter shading from dark to light. The three-part color region consists of a dark gray dorsal/back cape, a light gray side, and a white belly.
Individual dolphins are identified by their unique dorsal fins. Researchers take photographs of the dolphins' dorsal fins and then match the shape, nicks, and notches in each fin to a catalog of known individuals to obtain life history information for each animal.
Behavior and Diet
Spinner dolphins feed at night on species including small fish, shrimp, and squid that are found about 650 to 1,000 feet below the surface of the water. Spinner dolphin prey species follow a vertical and horizontal migration pattern, staying in deep waters in the ocean during the day, and then moving up in the water column (vertical migration) and inshore (horizontal migration) at night. Spinner dolphins take advantage of the nightly migration that brings their prey species to shallower depths and closer to shore by feeding throughout the night.
When resting, spinner dolphins move back and forth slowly as a single unit, with the animals in tight formation but spaced just out of contact with one another. They may engage in resting behaviors for about four to five hours daily. This behavior may vary seasonally, coinciding with the shifts in day length. During rest, spinner dolphins rely on vision rather than echolocation for scanning their environment. Group movements during rest are typically in open, sandy-bottom areas where predators are more visible.
At the end of their rest period, spinner dolphins usually abruptly increase their activity level, including their swim speeds, aerial behaviors, vocalizations, and make shorter dives than when resting. In 1994, researchers described spinner dolphins swimming in a “zig-zag” pattern following their rest period. They swam toward the open waters and then doubled back into shallower waters. This back-and-forth swimming repeats a zig-zag formation over most of the area, possibly functioning as a social cue for the entire group to coordinate their movement into the deeper seas. Likewise, the dolphins’ acoustic behaviors rise and fall synchronously with the zig-zag swimming patterns. When these patterns subside, the spinner dolphins swiftly race to the offshore waters of their foraging grounds, where they are sometimes joined by bottlenose or spotted dolphins. At this point, spinner dolphins’ dive times are extended and the dolphins begin their foraging movements.
Where They Live
In most places, spinner dolphins are found in areas of deep waters where they likely track prey. Although the pelagic stock of Hawaiian spinner dolphins are found in the deeper waters offshore of the islands, the rest of the Hawaiʻi population has a more coastal distribution. During daytime hours, the island-associated stocks of Hawaiian spinner dolphins seek sanctuary in nearshore waters, where they return to certain areas to socialize, rest, and nurture their young. These areas are typically in clear, calm, and relatively shallow waters. They usually have a sandy bottom that presumably provides an environment in which the dolphins are able to visually monitor for predators, as they cease echolocation while they rest. Spinner dolphins use a variety of bays and nearshore coastal waters throughout their range, but they seem to prefer certain bays.
Spinner dolphins are found throughout the world in tropical and warm-temperate waters. Four subspecies of spinner dolphins have been described worldwide:
- Stenella longirostris longirostris (also known as Gray’s spinner dolphin)—which includes the Hawaiian spinner dolphin—in the tropical Atlantic, Indian, and western and central Pacific Oceans.
- S. l. orientalis in the eastern tropical Pacific Ocean
- S. l. centroamericana near Central America
- S. l. rosiventris, the dwarf spinner dolphin, in southeast Asia to northern Australia
The Gray’s spinner dolphin is the typical form of spinner dolphin found in most areas of the world.
Lifespan & Reproduction
Like all marine mammals, spinner dolphins are slow reproducers. They live for about 20 years, with some individuals living for at least 25 years. Spinner dolphins may mate year-round, with multiple males mating with one female. Gestation is similar to other dolphin species and lasts approximately 11 months. Spinner dolphins calve year-round, generally about once every 3 years, and lactate often for 1 to 2 years. They reach sexual maturity at around 7 years of age.
Human Interactions and Viewing Pressure
Viewing wild marine mammals in Hawaiʻi has been a popular recreational activity for both tourists and residents over the past several decades. We estimate that there are upwards of 70 tour operators that provide dolphin-directed tours focused on Hawaiian spinner dolphins. More than 100 commercial boat tour and kayak tour operations may opportunistically view these animals.
Tours operate out of various harbors along most of the coasts of the main Hawaiian Islands, bringing guests to well-known locations for spinner dolphin viewing. Researchers have observed up to 13 tour boats at a time in some locations, with vessels jockeying for position on a single spinner dolphin group and more than 60 swimmers in the water attempting to closely interact with the dolphins at once. In addition, a number of residents and visitors venture on their own, independent of commercial operators, to view and interact with spinner dolphins. Some operators and various media outlets have encouraged the expectation for close interactions with wild dolphins, and routinely promote close vessel or in-water encounters with the dolphins. This contradicts established wildlife viewing guidelines.
Commercial operators and individuals interested in viewing or closely interacting with Hawaiian spinner dolphins increasingly target the dolphins' essential daytime habitats. Encounters with dolphins in these areas are very common due to the predictability of spinner dolphin behavior. Viewing spinner dolphins in their natural habitat can be an educational and enriching experience if conducted safely and responsibly from a distance. However, closely approaching, swimming with, pursuing, interacting, or attempting to interact with the dolphins could disrupt their daytime behaviors. Some interactions with people in essential daytime habitats may disturb individual dolphins or resting groups, even rising to the level of “take” under the Marine Mammal Protection Act, which is illegal.
Response to disturbance varies among individuals, but ultimately diverts time and energy from fitness-enhancing activities (such as resting and recuperating after an energetically-costly night of foraging for prey). These responses may, over time, result in negative effects to the fitness of individuals or resident populations. For example, lack of consistent, undisturbed resting periods can reduce the amount of energy available for a spinner dolphin to engage effectively in foraging activities at night. Over time, this can result in overall poor body condition, which reduces the dolphin’s ability to fight off disease, protect itself from predators, successfully reproduce, or rear young.
Peer-reviewed scientific literature has documented disturbance responses by individual spinner dolphins, as well as changes to spinner dolphin group behavior patterns over time. Individual dolphin responses include:
- Increased displays such as leaping, spinning, or tail slapping when closely approached by vessels and swimmers.
- Avoidance behaviors, including increased swimming speed and moving away from swimmers and vessels, or leaving the bay completely in response to human pursuit.
- Aggressive behaviors directed at people, including charging or threat displays.
Researchers have also documented changes to spinner dolphins’ behavior patterns in essential daytime habitats, including changes to patterns associated with aerial behaviors, residence times, and distribution within the habitat. Human-caused disturbances to daily behaviors may be incidents of 'take,' as defined (and prohibited) under the Marine Mammal Protection Act. The chronic nature of these problems in Hawaiʻi and the observed changes to behavioral patterns over time are a cause for concern for this dolphin population.
Marine debris is a growing concern within the marine environment, as it poses multiple threats to the marine ecosystem. For instance, spinner dolphins may ingest (either directly or through prey items) or become entangled in marine debris. These interactions may cause:
- Limited predator avoidance
- Internal or external wounds
- Skin lesions or sores
- Blockage of the digestive tract, resulting in starvation that often leads to death
- Reductions in quality of life and/or reproductive capacity
- Impairment of feeding capacity
- Introduction and/or concentration of damaging or toxic compounds to the animal.
The severity of the effects of debris interactions on all dolphin populations remains unclear because many deaths likely occur undetected at sea.
We do not have sufficient information to determine the severity of the threat of direct ingestion of large debris on spinner dolphin populations. Some data indicates that spinner dolphin prey species are consuming very small plastics. In 2010, researchers analyzed mesopelagic fish in the North Pacific Central Gyre and found that 35 percent of the fish—many of which were lantern fishes (spinner dolphins’ main prey)—had ingested plastic. Larger fish generally had more pieces of plastic in their guts than smaller fish. We are particularly concerned about the ability for plastic debris to absorb organic pollutants that may be toxic to the marine organisms that ingest them. These contaminants can bioaccumulate as they move up the food chain to top predators such as spinner dolphins. Scientists have also found high levels of butyltin and organochlorine (chemical compounds found in some plastics) in migrating lantern fish species in the Western North Pacific, which may indicate a cause for concern for predators, such as spinner dolphins.
Humans introduce sound intentionally and unintentionally into the marine environment. This could be from commercial and recreational ocean activities, navigation, oil and gas exploration and acquisition, research, and military activities. Spinner dolphins use sound to communicate, navigate, locate prey, locate predators, and sense their environment, which can be impacted by introduced anthropogenic noise How severely noise exposure affects dolphins and whales depends on factors including:
- Noise source
- Decibel level
- Distance between the source and the animal
- Characteristics of the animal (for example, hearing sensitivity, behavioral context, age, sex, and previous experience with sound source)
- Time of day or season (which affects how sound travels through the water)
In marine mammal populations, noise can seriously disrupt communication, navigational ability, and social patterns.
Spinner dolphins, like all marine mammals, can be susceptible to widespread disease. Outbreaks in spinner dolphins are not commonly reported, but scientists have previously detected serious diseases, such as toxoplasmosis and cetacean morbillivirus. Although the number of spinner dolphin deaths attributed to these diseases is fairly low (many are thought to be unreported), thousands of other marine mammal species have died from these diseases worldwide.
Hawaiian Spinner Dolphin
The Hawaiian population of spinner dolphins spend their daylight hours in coastal waters, generally in calm bays. They use these areas to rest, socialize, care for their young, and avoid predators. At night, they travel to deeper water 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.
A robust estimate for the population size of spinner dolphins is only available for the Hawaiʻi Island stock, which is estimated to be around 600 animals. The Kauaʻi/Niʻihau stock is estimated to be around 600 animals and Oʻahu/4-Islands stock is estimated to be around 300 animals. Both of these estimates lack data from the stocks' full ranges. Information is insufficient to provide estimates for the other three stocks.
Spinner dolphins are common and abundant throughout the entire Hawaiian Archipelago. Because of genetic differences between spinner dolphins throughout the islands and atolls, the population in Hawaiʻi has five distinct island-associated stocks. The stocks are as follows: 1) Midway/Kure, 2) Pearl and Hermes Reef, 3) Kauaʻi and Niʻihau, 4) Oʻahu/4-Islands (including Maui, Lānaʻi, Molokaʻi, and Kahoʻolawe), and 5) Hawaiʻi Island. These stocks live in coastal waters to 10 nautical miles from the shore of their resident island(s). 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. The genetic data suggest that these stocks are reproductively isolated populations, meaning that there is little to no breeding between stocks.
In the Spotlight
Spinner dolphins, like all marine mammals, are protected under the Marine Mammal Protection Act (MMPA). NOAA Fisheries is dedicated to conserving spinner dolphin populations through numerous management and regulatory actions.
All marine mammals are protected from "take" under the MMPA. The MMPA defines take to mean: "to harass, hunt, capture, or kill" any marine mammal or attempt to do so. Harassment is further defined as any act of pursuit, torment, or annoyance which has the potential to do the following:
- Level A harassment—injure a marine mammal or marine mammal stock in the wild.
- Level B harassment—disturb a marine mammal or marine stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering.
When viewing spinner dolphins in the wild, people must ensure their activities will not result in "take." Activities that result in take can include close approach to dolphins, by vessel or any other means, including activities like swimming with the dolphins. The MMPA does not specify the distance at which harassment is likely to occur for spinner dolphins; however, any activity that disturbs these animals can be considered 'take,' and is therefore illegal. NOAA Fisheries recommends staying at least 50 yards away from spinner dolphins to view them safely and to minimize illegal take.
Current Management Issues
Resident populations of Hawaiian spinner dolphins feed offshore throughout the night and return to the coast of Hawaiʻi coasts to rest during the day. Hawaiian spinner dolphins rest in the sheltered bays of Hawaiʻi and along its coastlines, which overlaps with areas that humans use to recreate. They are one of the most easily encountered cetaceans in the waters of the main Hawaiian Islands, and thus 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. These chronic disturbances to resting dolphins can negatively affect their health, fitness, and ultimately their survival.
Based on extensive analysis using the best scientific information available, feedback from the public, and consultation with enforcement officials, NOAA Fisheries has determined that the rules currently in place to implement the MMPA should be made more specific for Hawaiian spinner dolphins. This will more effectively prevent potentially harmful impacts of increased interaction pressures on these animals. NOAA Fisheries’ Pacific Islands Regional Office published a proposed rule to protect spinner dolphins from human activities in August, 2016. A final rule is in development.
Promoting Responsible Wildlife Viewing
NOAA Fisheries has developed wildlife viewing guidelines for spinner dolphins and other protected species to help the public understand how to responsibly and legally view these animals. To be compliant with the law, it is best to follow the guidelines.
- Six reasons why you should not swim with wild spinner dolphins
- Marine Life Viewing Guidelines
- Viewing Marine Wildlife in Hawaiʻi
- Be Dolphin SMART
Overseeing Marine Mammal Health and Stranding Response
We work with volunteer networks in all coastal states to respond to marine mammal strandings including all dolphins and porpoises. When stranded animals are found alive, NOAA Fisheries and our partners assess the animal’s health and determine the best course of action. When stranded animals are found dead, our scientists work to understand and investigate the cause of death. Although the cause often remains unknown, scientists can sometimes attribute strandings to disease, harmful algal blooms, vessel strikes, fishing gear entanglements, pollution exposure, and underwater noise. Some strandings can serve as indicators of ocean health, giving insight into larger environmental issues that may also have implications for human health and welfare.
Marine Mammal Unusual Mortality Events
Spinner dolphins have been part of a declared unusual mortality event in the past. Under the Marine Mammal Protection Act, an unusual mortality event is defined as "a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response." To understand the health of marine mammal populations, scientists study unusual mortality events.
Dolphin-Safe/Tuna Tracking and Verification Program
Dolphins, like other marine mammals, may become bycatch in fisheries. Some species of tuna are known to aggregate beneath schools of certain dolphin stocks. In some parts of the world, this close association led to the fishing practice of encircling a dolphin school to capture the tuna concentrated below, to the detriment of the dolphins, which would get trapped in the net. The Dolphin Protection Consumer Information Act established a national tuna tracking program to ensure that tuna imported into the United States meets certain requirements to ensure the safety of dolphins during tuna fishing operations.
Dolphin SMART is a partnership program that was developed by NOAA Fisheries, NOAA Office of Marine Sanctuaries, the Whale and Dolphin Conservation, and the Dolphin Ecology Project. The goal of the program is to promote responsible stewardship of wild dolphins. The acronym SMART stands for:
S = Stay back 50 yards from dolphins
M = Move away cautiously if dolphins show signs of disturbance
A = Always put your engine in neutral when dolphins are near
R = Refrain from feeding, touching, or swimming with wild dolphins
T = Teach others to be Dolphin SMART
In 2005, NOAA Fisheries convened a Spinner Dolphin Working Group to enhance protections for Hawaiian spinner dolphins from human disturbance. This group consisted of individuals from the Marine Mammal Commission and state and federal agencies that participate in spinner dolphin research and conservation. We used deliberations from this working group to inform an Advance Notice of Proposed Rulemaking that was published in the Federal Register in December 2005. A Notice of Intent (NOI) to Prepare an Environmental Impact Statement followed, in which we identified five preliminary alternatives for consideration and comment:
- Partial (time-area based) closures for certain spinner dolphin resting habitats
- A No Action Alternative
- Establishing a minimum distance limit
- Regulation of human behavior while in NOAA Fisheries-identified spinner dolphin resting areas
- Complete closure of all known spinner dolphin resting areas in the main Hawaiian Islands
This notice invited information from the public on the scope of the issues that should be addressed in the Draft Environmental Impact Statement (DEIS), the issues of concern regarding practical considerations involved in applying the proposed regulations, and the identification of environmental and socioeconomic concerns to be addressed in the analysis. The notice also sought to determine whether NOAA Fisheries addressed the appropriate range of alternatives.
On August 23, 2016, NOAA Fisheries published the DEIS and 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, Lānaʻi, and Kahoʻolawe where spinner dolphins are found throughout the day. A final rule to enhance protections for Hawaiian spinner dolphins is anticipated in 2021.
Key Actions and Documents
Incidental Take Authorization: Scripps Institute of Oceanography Low-Energy Geophysical Survey in the South Atlantic Ocean
- Issued IHA (pdf, 16 pages)
- IHA Application (pdf, 114 pages)
- References (pdf, 42 pages)
- Biological Opinion (pdf, 188 pages)
- Draft IHA (pdf, 15 pages)
- Issued IHA (pdf, 13 pages)
- IHA application (pdf, 115 pages)
- Draft IHA (pdf, 13 pages)
- References (pdf, 45 pages)
- Biological Opinion (pdf, 161 pages)
- Letter of Authorization (pdf, 33 pages)
- Revised LOA Application (pdf, 325 pages)
- LOA Application (pdf, 318 pages)
- Monitoring and Reporting
- Notification and Reporting Plan (pdf, 4 pages)
- Biological Opinion
- Environmental Impact Statement
- Public Comments
- NRDC Comment Letter (pdf, 37 pages)
- References (pdf, 25 pages)
Incidental Take Authorization: U.S. Navy Hawaii-Southern California Training and Testing (HSTT) (2018-2025)
- Final Rule for 2 Year Extension
- Proposed Rule for 2 Year Extension
- Notice of Receipt of Application for 2 Year Extension
- Final Rule
- Proposed Rule
- Notice of Receipt of Application for LOA
- LOA for Testing (pdf, 38 pages)
- LOA for Training (pdf, 38 pages)
- Application for Extension (pdf, 84 pages)
- LOA and Rule Application (pdf, 580 pages)
- Monitoring Reports (External Link)
- Environmental Impact Statement (External Link)
- Mitigation Addendum (pdf, 12 pages)
- Notification and Reporting Plan (pdf, 4 pages)
- Final Biological Opinion (pdf, 683 pages)
- Final Biological Opinion Amended ITS 2020 (pdf, 8 pages)
- Public Comments (External Link)
- References (pdf, 15 pages)
NOAA Fisheries conducts various research activities to learn about the biology, behavior, and ecology of spinner dolphins. This research informs management decisions and enhances recovery efforts for spinner dolphin populations.
Determining the size of spinner dolphin populations helps resource managers determine the success of conservation measures. Our scientists collect population information and present the data in annual stock assessment reports.
Long-term photo-identification (photo-ID) studies provide insight into habitat use, movements, and life history characteristics of individual spinner dolphins. Some species of cetaceans have unique, naturally occurring markings on their bodies or dorsal fins. We use photographic records of these scars, nicks, notches, or color patterns to identify individuals. We also archive our photographs of spinner dolphins with other sighting data, such as location, group size and structure, and behavior. We can then track individual cetaceans over time and between locations on the basis of these photo-IDs.
Our cetacean scientists conduct photo-ID research throughout the Hawaiian Islands, at Palmyra Atoll, and around Guam and the Commonwealth of the Northern Mariana Islands. These long-term studies will help establish new stock boundaries for island-associated cetaceans in each region. Once we establish the photo catalogs, we can also use them to evaluate species abundance using mark-recapture techniques.
Our cetacean scientists are active participants in the Pacific Islands Photo-Identification Network (PIPIN). This group of researchers from the Hawaiian Islands studies spinner dolphins and uses photo-ID as a primary research tool. PIPIN is creating a collaborative photo-ID database of spinner dolphin populations within the Hawaiian Islands. This will help us study movements of dolphins between islands (if they occur), and to determine if dolphin populations differ from one island to the next. Results of the cooperative studies will help managers assess and resolve issues with human-dolphin interactions, such as effects on spinner dolphins arising from "swim-with-dolphins" tourism operations.
Hawaiian Islands Cetacean and Ecosystem Assessment Survey
The Hawaiian Islands Cetacean and Ecosystem Assessment Survey (HICEAS, pronounced "high-seas") is a large-scale ship survey for whales, dolphins, and seabirds within the U.S. waters of the Hawaiian Islands. The study area is approximately 1.8 million square nautical miles, which includes waters surrounding all Northwestern and main Hawaiian Islands out to 200 nautical miles offshore. Waters within this 200 nautical miles boundary around the Hawaiian Islands are referred to as the U.S. Exclusive Economic Zone.
HICEAS is a collaboration between the Pacific Islands Fisheries Science Center located in Honolulu, Hawai`i, and the Southwest Fisheries Science Center located in La Jolla, California. NOAA Fisheries has conducted HICEAS in 2002, 2010, and 2017. The goals are to estimate how many whales and dolphins are in Hawaiian waters, examine their population structure, and understand their habitat.
There are four major research components to HICEAS:
- Visual observations for cetaceans, including photo-ID, biopsy sampling, and satellite tagging.
- Passive acoustic monitoring using towed hydrophone arrays and other tools.
- Ecosystem assessment, including visual surveys for seabirds and measurement of oceanographic variables.
In the winter of 2020, another research cruise, the Winter Hawaiian Islands Cetacean and Ecosystem Assessment Survey (WHICEAS; pronounced “why-seas”) was conducted to focus on baleen whales that may migrate to the area during this time and to examine changes in density of other species between winter and summer. Like HICEAS, this project also used traditional cetacean survey methods such as visual observations and acoustic detections.
Other ancillary projects, such as aerial photogrammetry using a hexacopter, testing of new passive acoustic tools, and projects that support and augment our assessment mission.
Recent Science Blogs
Injury Determinations for Humpback Whales and Other Cetaceans Reported to NOAA Response Networks in the Hawaiian Islands During 2018
During 2018, there were 19 reports of cetaceans with human-caused injuries, including 4 humpback…
A complete list of all references cited in the Hawaiian spinner dolphin proposed rule.
Outreach & Education
This sign is often posted near boat ramps, piers, docks, marinas, and waterfront parks.
This sign is often posted near boat ramps, piers, docks, marinas, and waterfront parks.