Spinner dolphins (Scientific name: Stenella longirostris) are smaller than bottlenose dolphins and are named for their spinning leaps. They are generally about two meters long (6 to 7 feet) and weigh between 60 and 80 kilograms (130 to 170 pounds). They have three shadings: 1) dark gray on their back and on their dorsal fin; 2) blue-grey in the middle and 3) white on their bellies. They have sharper snouts than bottlenose dolphin and slimmer bodies. Long-snouted spinner dolphins are known for their acrobatic skills. Found in tropical waters, they can jump three meters (10 feet) in the air and have been observed spinning seven times in a single leap.
Spinner dolphins are best known for their above-water displays of leaping and spinning several times. They often appear to be awake during their sleep cycles. This is because only one half of their brain gets rest, while the other half is used to help them move through waters. NOAA says disturbing sleeping spinner dolphins can result in various health and reproduction issues, and may cause the mammals to get aggressive.
Spinner dolphins are estimated to live about 20 years on average. The maximum age recorded in the wild was 26 years. Spinner dolphins are often attacked by sharks. The wound and scar marks found on some dolphins indicate attack by the small squaloid shark and other larger sharks. Spinner dolphins are also threatened by the chase and capture techniques used by commercial fisherman to catch yellowfin tuna. Yellowfin tuna follow spinner dolphins in search of food. This relationship is probably mutualistic.
Websites and Resources: Britain-based Whale and Dolphin Conservation Society uk.whales.org ; Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Spinner Dolphin Subspecies and Where They Are Found
Spinner dolphins are native to the Indian Ocean, Atlantic Ocean and Pacific Ocean. They live in tropical and subtropical marine environments between 40°N and 40°S latitudes and can be found around reefs, near the shores of continents and islands, other coastal areas and in the open sea. They are typically found near the surface but can dive to depths of 400 meters (1312 feet). In the U.S. they can be found off New England and Mid-Atlantic, Pacific Islands and the Southeast. [Source: Cassandra Mac, Animal Diversity Web (ADW) /=]
There are five different geographic morphs: 1) Gray's spinner dolphins, also known as Hawaiian spinner dolphins (S. l. longirostris), the most common form. found in most areas of the world, except for some parts of tropical Asia and the eastern tropical Pacific; 2) Eastern spinner dolphins ( S. l. orientalis), found only in the waters of the far-eastern tropical Pacific Ocean, predominantly offshore; 3) Central American spinner dolphins (S. l. centroamericana), found only in the coastal waters of the eastern tropical Pacific near Central America; 4) dwarf spinner dolphins (S. l. roseiventris), common in the waters of Southeast Asia and northern Australia; and 5 )Whitebelly spinner dolphins (a hybrid between Gray's spinner dolphins and eastern spinner dolphins), found in the eastern tropical Pacific. Whitebelly spinner dolphin distribution overlaps with Gray's spinner dolphins. Adaptations to specific environmental conditions in different parts of the range are believed to underlie the emergence of subspecies and associated differences in physical appearance, mating system, and more. /=\
Some spinner dolphins live predominantly offshore, especially those in the eastern tropical Pacific. Other populations rest during the day in shallow, coastal waters and stay in sandy-bottomed bays or around coral atolls. Although these dolphins tend to remain close to the surface, where they are found is often related to the topography of the oceanic floor far below them. They are much more common in places where the ocean bottom is mountainous and sloping than where it is a flat, abyssal plain. Spinner dolphins often gather near places where currents converge, diverge and rise up of the ocean floor as these are places with high concentrations of plankton, fish and squid.
Stenella — Spinner, Spotted and Striped Dolphins
Spinner dolphins belong to the genus Stenella, which also includes spotted dolphins, and striped dolphins and is comprised of five species of dolphins: pantropical spotted dolphins (Stenella attenuata), Atlantic spotted dolphins (Stenella frontalis), striped dolphins (Stenella coeruleoalaba), spinner dolphins (Stenella longirostris), and Clymene dolphin (short-snouted spinner dolphin, Stenella clymene. Stenella dolphins are a part of the family Delphinidae which consists of dolphins, killer, whales, pilot whales, and their relatives. Dolphins are part of the suborder Odontoceti better known as the toothed whales. They are also part of the bigger order Cetacea which is comprised of all marine mammals. [Source: Abigail Ross, Animal Diversity Web (ADW) /=]
Stenella dolphins are smaller in size compared to many other dolphins and toothed whales. They typically have beak-shaped rostrums (snouts) that vary lengths and often feed pelagic (open ocean) marine life such as lanternfish, squid, shrimp, and pelagic fishes. They're beak length can range from 11 to 20 centimeters (4 to 8 inches). All the species can be found in groups-known as pods that reach have hundreds of individuals.
Of the five species of dolphins in genus Stenella, two of the species — Clymene dolphins and Atlantic spotted dolphins — are endemic to the Atlantic Ocean, Gulf of Mexico, and Caribbean. The other three species — Pantropical spotted dolphins, spinner dolphins and striped dolphins — are found in the Atlantic, Pacific and Indian Oceans, mainly in warmer waters.
Stenella often have markings that are white or light grey in color and appear all over the back and are most numerous between the head and the dorsal fin. These markings can appear as speckles, spots, or stripes. They can also have some markings or none at all on their bottom side. Newborn Stenella they have no spots, and their coloring is often dark purplish grey. As they grow older their coloring becomes more distinctly grey, differences between the dorsal and ventral sides become more pronounced and markings appear and become bigger, more numerous and spread over larger areas. They can have dark patches or bands of color around the eyes, blowhole, fins, and tail.
Clymene dolphins (Scientific name: Stenella clymene) are also known as "short-snouted spinner dolphins" because they often spin while jumping out of the water. They are related to spinner dolphins. But unlike spinner dolphins, however, they do not complete a full rotation during their spins. Instead, they usually land on their sides or backs. [Source: NOAA]
Clymene dolphins are found in deep tropical, subtropical, and temperate waters throughout the Atlantic Ocean. They are the smallest dolphin in the genus Stenella, which also includes spinner dolphins, Atlantic spotted dolphins, pantropical spotted dolphins, and striped dolphins. The range of Clymene dolphins includes the waters of the northwestern Atlantic (New Jersey), the Gulf of Mexico, the Caribbean Sea, southern Brazil, and West Africa (Mauritania to Angola). They prefer deep waters off the continental shelf (the edge of a continent below the ocean’s surface). They are usually found in oceanic waters 250 to 5,000 meters (820 to 16,400 feet) deep.
Clymene dolphins are about 1.8 to 2 meters (6 to 6.5 feet) long and weigh about 75 to 90 kilograms (165 to 200 pounds). They have a streamlined body with a tall, curved dorsal fin located midway down their back. Their beaks are moderately short. Like other cetaceans, their head has a distinctive "melon," a rounded forehead that collects sounds from the environment. Clymene dolphins have a three-part color pattern with a dark gray back, light gray sides, and a white or pale gray underside. They have distinct black lips that can look like a mustache, as well as a dark line that extends across the top of their beak. They also have 39 to 52 pairs of small, cone-shaped teeth in each jaw.
Clymene dolphins are usually found in groups of 60 to 80 individuals but sometimes travel in groups of several hundred. These groups are sometimes organized by sex. They are often described as “acrobatic” swimmers because they often leap out of the water, spin in the air, and “surf” in the waves created by vessels. They have been reported to spin up to three to four revolutions out of the water. They sometimes interact with other cetacean species, such as common dolphins off West Africa and spinner dolphins in the Caribbean Sea. [Source: NOAA]
Clymene dolphins dive to catch small fish and cephalopods (such as, squid and octopi). They have 39 to 52 pairs of small, cone-shaped teeth in each jaw. They sometimes feed at night to catch prey that migrate towards the water’s surface after dark. Little is known about their reproductive habits. These dolphins reach sexual maturity once they are 1.8 meters (6 feet) long. Females give birth to a single calf that weighs about 10 kilograms (22 pounds). Threats include entanglement in fishing gear and ocean noise. They are sometimes hunted in the Caribbean Sea.
The worldwide population of Clymene dolphins is unknown. In U.S. waters, they are divided into two stocks: the northern Gulf of Mexico stock and the western North Atlantic stock, with more than 100 in the former and an unknown number in the latter. CITES places them in Appendix II, which lists species not necessarily threatened with extinction now but may become so unless trade is closely controlled. Like all marine mammals, they are protected under MMPA throughout their range. Threats include entanglement in commercial fishing gear, specifically, gillnet operations in Venezuela and tuna purse seine nets off the coast of West Africa. Ocean noise is also a threat, Whalers in the Caribbean Sea sometimes target and hunt Clymene dolphins for meat and oil.
Spinner Dolphin Physical Characteristics
Compared to other dolphins, spinner dolphins are relatively small and slim. They range in length from 0.84 to 1.7 meters (2.8 to 5.5 feet) and range in weight from 23 to 80 kilograms (50 to 175 pounds). They are endothermic (use their metabolism to generate heat and regulate body temperature independent of the temperatures around them),homoiothermic (warm-blooded, having a constant body temperature, usually higher than the temperature of their surroundings) and are polymorphic (“many forms”), in which individuals can be divided into easily recognized groups, based on structure, color, or other similar characteristics).
Sexual Dimorphism (differences between males and females) is relatively minor but exists. Males are larger than females and males and females have different shapes. In females, the posterior portion of the body is longer, thus allowing room for the calf to grow and develop; the girth is smaller, especially near the anus; and both the dorsal fin height and fluke span are smaller. It is believed that the degree of sexual dimorphism in spinner dolphins is correlated with mating system.
According to Animal Diversity Web: The body is torpedo-shaped but irregular. The dorsal fin is triangular in shape, but the tip can vary so that it is directed anterior (canted), posterior (falcate), or straight up (erect), depending on the geographic morph. Usually, these dolphins are tripartite, having a three-layered skin pattern with a dark grey back (dorsal), light grey sides, and a white belly (ventral), but the physical appearance is highly dependent on the geographic range of the subspecies, as described below. [Source: Cassandra Mac, Animal Diversity Web (ADW) /=]
In Gray's spinner dolphins, adult females range from 1.39 to 2.04 meters and adult males, from 1.60 to 2.08 meters. They exhibit the tripartite pattern and have a falcate dorsal fin, a small or non-existent post-anal hump, and relatively small dorsal fin and flippers. In eastern spinner dolphins, adult females are between 1.52 and 1.93 meters and adult males are from 1.60 to 1.99 meters. They are a monotone steel grey color and have white patches around the genitals and axillary line. They have a relatively long beak and are highly sexually dimorphic, especially when compared to the other subspecies. Males have a strongly forward-canted dorsal fin, a medium to large post-anal hump, upturned fluke tips, and smaller testis compared to the males of other subspecies.
In Central American spinner dolphins, adult females are between 1.75 and 2.11 meters and adult males can reach over 2.16 meters, making this the largest subspecies of spinner dolphin. Like eastern spinner dolphins, they are a monotone grey color, but they lack the white patches and have an even longer beak than eastern spinner dolphins. They also have a pronounced Sexual Dimorphism (differences between males and females): similar to eastern spinners, that is, a strongly canted dorsal fin, a large post-anal hump, and upturned fluke tips.
In dwarf spinner dolphins, adult females range between 1.38 and 1.45 meters and adult males are between 1.29 and 1.58 meters, making this the smallest subspecies. They have a tripartite color pattern, an erect or falcate dorsal fin, and relatively large flippers and dorsal fin. Sexual Dimorphism (differences between males and females): in this subspecies is not marked. Whitebelly spinner dolphins appear to be a hybrid between Gray's spinner dolphins and eastern spinner dolphins and it is a morphological intermediate between the two. The dorsal fin is either falcate or erect, and males have large testis.
Stenella Dolphin Behavior
Stenella dolphins, which include spinner dolphins, live in pods made of individuals of both sexes and often organized by sex, age, and breeding status. They are an extremely social species, and are known for interacting with other species of whales and dolphins as well as other marine animals, and sometimes even humans. Striped dolphins tend to be less social and interact with other organisms less frequently than the other four Stenella species. Stenella species have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates). [Source: Abigail Ross, Animal Diversity Web (ADW) /=]
During the day Stenella dolphins stay near the surface and at night dive down to feed. They swim in zig zag or back and forth patterns moving between shallow and deeper waters, as well as engage in periods of rest. During these rest periods pods swim close to one another in a slow back and forth swaying motion. The periods of rest typically take place multiple times a day for around three to five hours at a time.
Stenella dolphins dolphins are very playful. Both calves and adults engage in playtime with each other. Play consists of jumping out of the water and flipping or spinning, as well as "roto-tailing" — jumping high above the water and rotating their tail. Striped dolphins "roto-tail" more than other species. The dolphins may use spinning to communicate with each other, or to remove parasites from their bodies. Play also consists of blowing bubbles or shooting water from the blowholes, mock chasing schools of fishes, and playing with pieces of seaweed.
Seaweed play involves picking up a piece of seaweed and placing it on a flipper, and then tossing it back and forth between their flippers, beak or tails. Most often a single dolphin plays with the seaweed but sometimes two or three dolphins all pass a piece of seaweed back and forth. More often a single piece of seaweed is shared between individuals who take turns playing with it. Some swim up to boats and ride the bow waves or surf the wake of the boats.
Spinner Dolphin Behavior
Spinner dolphins are nocturnal (active at night), motile (move around as opposed to being stationary), nomadic (move from place to place, generally within a well-defined range), and social (associates with others of its species; forms social groups). In terms of home range, The home range size of spinner dolphins is not known and probably differs among subspecies. [Source: Cassandra Mac, Animal Diversity Web (ADW) /=]
Spinner dolphins get their name from their habit of leaping in the air and spinning around. Some scientists say such behavior is not always playfulness and can instead be an attempt to alert others to danger. Spinner dolphins hunt in offshore waters at night. During the day, they use areas close to shore that have optimal environmental conditions to socialize, nurture their young, hide from predators and rest in preparation for nightly hunting. [Source: Associated Press]
According to Animal Diversity Web: Spinner dolphins are well known for their aerial behaviors, which can be divided into different actions, including spins, leaps, tail-over-head leaps, backslaps, headslaps, noseouts, tailslaps and any combination of these. These behaviors are good predictors of daily activity patterns, can reveal the activity state of a school, and play an essential role in communication. . This is a social species and individuals form schools, which are ever-changing and can vary in size.
Physical contact between individuals while swimming is common. Some populations of Eastern spinner dolphins are even known to school with populations of spotted dolphins. It is believed that this provides protection during resting, since spotted dolphins feed in the daytime and spinner dolphins feed at night. This resting strategy works for eastern spinner dolphins because they occur primarily offshore. However, Gray’s spinner dolphins, which spend much more time near the coast, often spend the day in “rest areas,” which are shallow areas generally less than 50 meters deep in which dolphins can enter into what is known as a ‘quiescent period.’ These rest areas are relatively close to drop-off’s of very deep water so that the animal can be ready to hunt for prey at nightfall./=\
Spinner Dolphin Communication
Spinner dolphins sense using vision, touch, sound, vibrations, and chemicals usually detected by smell. and echolocation (emitting sound waves and sensing their reflections to determine the location of objects) and communicate with vision, sound, vibrations and choruses (joint displays, usually with sounds, by individuals of the same or different species). [Source: Abigail Ross, Animal Diversity Web (ADW) /=]
The distinct aerial behaviors for which spinner dolphins are known function primarily to make noise and thus communicate with other individuals within a school, specifically when individuals are not within each other’s sight. Most, if not all of the different behaviors make a noise which is believed to travel in all directions. These dolphins also have a sound generation and beaming apparatus that sends vocal signals via clicks (a type of echolocation (emitting sound waves and sensing their reflections to determine the location of objects)) in a single direction. /=\
Stenella dolphins communicate using a wide range of auditory cues and sounds, as well as using some visual cues and echolocation. Their main sources of communication are auditory sounds and acoustic signaling. They make a variety of sounds including whistles, clicks, click trains (repetitions of multiple clicks), squeaks, squeals, squawks, barks and chirps. Used in mating, hunting and prey spotting, as well as predator avoidance, acoustic signals consist of patterns that rise and fall in a synchronous manner.
Dolphins use echolocation to scan the environment, find prey, avoid predators, find other dolphins, and detect objects from a distance. They perform echolocation by sending out a series of clicks, which create sound waves that travel until bouncing off an object and then come back to the dolphin, providing information about composition of the object and how far away it is.
Spinner Dolphin Feeding and Predators
Spinner dolphins feed mainly at night on a wide variety of mesopelagic fish, especially lanternfis, which inhabit the intermediate depths of the sea, between about 200 and 1,000 meters (650 and 3,300 feet) down. They also eat squid that reside in the same depths and even some crustaceans that migrate every night from the ocean depths to the surface in search of their own food. Spinner dolphins may go as deep as 400 meters in search of prey. [Source: Cassandra Mac, Animal Diversity Web (ADW) /=]
Stenella dolphins diet consists of a wide variety of small fishes, cephalopods, mollusks, crustaceans and other small invertebrates. Typical prey includes squids, shrimp, lantern fish, conger eels, flounder, jacks, needlefish and octopuses. Some have preferences for certain prey, but most tend to feed on anything eatable that passes their way. Their prey often migrate vertically towards the surface at night. Pods of dolphins engage in cooperative hunting for their prey. They are able to catch their prey by surrounding them, and then taking turns swimming at and grabbing the surrounded prey. [Source: Abigail Ross, Animal Diversity Web (ADW) /=]
Stenella dolphins are considered apex predators and do not have very many predators except sharks, killer whales, false killer whales and short finned pilot whales. Among the individuals that are most at risk are pregnant females, lactating females, young calves and juveniles. Sharks and whales preying on dolphins harass the dolphins and attempt to subdue and separate their prey from the pod and killing it by biting and removing chunks of flesh from their prey. Adult dolphins protect calves by engaging in group chasing of the nearby predator and harassing and pestering them until the predator leaves.
Spinner Dolphin Mating, Reproduction
Spinner dolphins are viviparous, meaning they give birth to live young that developed in the body of the mother. Females give birth to a single calf roughly every three years. The average gestation period is 10.6 months. The weaning age ranges from 10.1 to 17.5 months. On average females reach sexual maturity at age five years, while males do so at six to 11.5 years. Pregnancy rates decreases after 11.5 years of age on average. [Source: Cassandra Mac, Animal Diversity Web (ADW) /=]
Females have an estrous cycle, which is similar to the menstrual cycle of human females. Reproduction is characterized by three stages: calving, lactation, and a period of inactivity or estrus. Because their gestation period is around 12 months the mating and calving seasons are around the same time. There are two primary seasons for mating and calving — the spring and the fall. However times of high reproductive activity can vary from year to year, and may occur during the summer. There are breeding seasons but they vary geographically. For instance, eastern spinners are most likely to mate in June and July while northern whitebelly spinners are best prepared for breeding in February and July and August.
Spinner dolphins are polygynous (males having more than one female as a mate at one time) and polygynandrous (promiscuous), with both males and females having multiple partners. Sexual interactions can occur in male-female pairs and male-male pairs. The mating system varies among subspecies and is related to the degree of sexual dimorphism which in turn reflects geographical range. Male testes size and the degree of sexual dimorphism in the shape of the dorsal fin are good indicators of the mating system. /=\
Males and females seeking mates engage in playful activities with each other such as chasing each other and making lots of noises that include whistles, clicks, and burst-pulse signals. Males often gently tap their fins on the fins and belly of females, and then rub, nudge, and gently bite the female. To impregnate the female the male moves below the female with his belly up, so that male and female are belly to belly when sexual intercourse occurs. Intercourse is typically very quick, lasting only a few seconds or a few minutes. [Source: Abigail Ross, Animal Diversity Web (ADW)]
According to Animal Diversity Web: In eastern spinner dolphins, which have higher Sexual dimorphism and smaller testis than other subspecies, pre-mating competition for access to females is intense, which on the population level leads to fewer males mating, and what is probably a polygynous mating system.In contrast, whitebelly spinner dolphins have much lower Sexual dimorphism and much larger testis relative to body size.
A larger proportion of males mate, which makes sperm and post-mating competition much more important. The result is a polygynandrous, or promiscuous, mating system. Based on this, we can infer that Gray's spinner dolphins are most likely polygynandrous as well because their behavior and reproduction is very similar to that of whitebelly spinner dolphins. Similarly, one can hypothesize that the Central American spinner dolphin, which has a high degree of Sexual dimorphism is probably polygynous, and the Dwarf spinner dolphin, which has reduced Sexual dimorphism is probably polygynandrous. /=\
Spinner Dolphin Offspring
Among spinner dolphins, as is true with all dolphins, parental care is provided by females. Pre-birth provisioning and pre-weaning and pre-independence provisioning and protecting are done by females. The post-independence period is characterized by the association of offspring with their mothers. Stenella dolphins are cooperative breeders (helpers provide assistance in raising young that are not their own) with females in a pod often helping to take care of calves that are not their own. Older females have fewer calves, but their calves are nursed for a longer period of time. Males for the most part are not involved in parenting.
Young are precocial. This means they are relatively well-developed when born. Parental care is provided by females and pre-independence protection is provided by females. The average length of a calf at birth is 77 centimeters (2.5 feet). There is an extended period of juvenile learning. /=\
Calves nurse between 10.1 and 17.5 months. Young calves are usually always near their mother or another adult. The social bond between mother and offspring continues throughout life. It takes calves about one to three years to reach the juvenile stage and full growth. While calves are nursing they tend to stay close to their mothers. Females can be pregnant and lactating at the same time, and gives birth to only one calf per pregnancy.
Humans, Spinner Dolphins and Conservation
Spinner dolphins as a whole are not considered endangered but some populations and subspecies may be. They are listed “ Data Deficient” on the The International Union for Conservation of Nature (IUCN) Redlist of Threatened Species. The Convention on International Trade in Endangered Species (CITES) places spinner them in Appendix II, which lists species not necessarily threatened with extinction now but may become so unless trade is closely controlled: They are protected by the Marine Mammal Protection Act (MMPA), which list the U.S. Eastern stock as depleted.
Spinner dolphins, along with spotted dolphins, are often associated with yellowfin tuna because the tuna follow them in search of food. As a result, tuna purse-seining fishermen get a good indication of where to find the highly valued tuna by locating schools of these spinner dolphins, specifically those that inhabit the eastern tropical Pacific Ocean. These dolphins are also an important in ecotourism. [Source: Cassandra Mac, Animal Diversity Web (ADW) /=]
Threats to spinner dolphins include entanglement, illegal feeding and harassment, habitat degradation, noise, disease and vessel collisions. Spinner dolphin populations are affected as by-catch in the yellowfin tuna purse-seine fisheries. Although the number of direct dolphin mortalities has decreased since the 1960s, from hundreds of thousands per year to 5000 dolphins annually in the 1990s, the population has not recovered as expected.
Swimming with Hawaii’s Spinner Dolphins is Banned
Swimming with dolphins is a popular tourist activity in Hawaii. Several companies offer tours that take swimmers to areas frequented by dolphins with the aim of giving them an opportunity to get in the water with the animals. Swimmers and boats that come to visit wild spinner dolphins close to shore during the day could be disturbing their rest and potentially harming them.
In September 2021, federal regulators banned swimming with Hawaii's spinner dolphins to protect the nocturnal animals from people seeking close encounters with them when they are trying to get some sleep. Swimming with resting spinner dolphins may constitute "harassment" under the Marine Mammal Protection Act. Any act of pursuit, torment, or annoyance that has the potential to disrupt a marine mammal's behavior is "harassment" under this Act and is, therefore, against the law. [Source: NOAA, September 28, 2021]
In addition, a new law in Hawaiʻi, effective October 28, 2021, prohibits swimming with, approaching, or remaining within 50 yards (45.7 meters) of a Hawaiian spinner dolphin (46 meters) of a spinner dolphin that is within 2 nautical miles (4 kilometers) of the shore of the main Hawaiian Islands. The rule applies to boats, canoes, stand-up paddleboards, drones or other objects. NOAA also is proposing a regulation that would prohibit entering certain areas between 6 a.m. and 3 p.m. in parts of the Big Island and Maui that are considered essential daytime habitats for spinner dolphins. [Source: Associated Press, September 29, 2021]
Reasons Why You Should Not Swim with Wild Spinner Dolphins
Wild spinner dolphins feed off-shore at night and return to sheltered bays and coastlines during the day to rest, socialize, tend to their young, and avoid predators. Any energy used towards responding to human activity—even if they appear to just be curious and enjoy the interaction—is energy not being used for these behaviors that are critical for survival. When their rest is interrupted, especially if it happens many times in a day, it can affect their health and well-being. [Source: NOAA, September 28, 2021]
Frequent close encounters with wild spinner dolphins, like swimming with or closely approaching spinner dolphins, can cause harm. Numerous studies found that close encounters with human activity can significantly disrupt spinner dolphins’ natural behavior. In some dolphin populations around the world, frequent close interactions with humans have been linked to biologically significant impacts, such as habitat abandonment, reduced female reproductive success, impeded activity and energy budgeting, and increased vigilance.
Although spinner dolphins may not appear to be sleeping when you see them in near-shore waters, they often are. Spinner dolphins have to move and breathe while resting and therefore swim slowly and occasionally surface for air while allowing half their brain to sleep at a time. It is important to stay back and give them enough space (at least 50 yards/45 meters) and not swim with them so that they can get enough sleep to survive.
If spinner dolphins are regularly disturbed while in their nearshore resting habitat, they may be forced to move to another location that's less protected, putting themselves at risk from predators like sharks. They may also be forced to use more energy to reach this location–energy that would otherwise be used to breed, nurse, and take care of their young. Hawaiian spinner dolphins choose certain sheltered, sandy bottom areas to rest because they are close to their feeding sites and the white sand background makes it easier for them to see predators.
Wild dolphins must maintain natural behaviors to thrive in the wild. The wild dolphins you encounter are not trained dolphins in an aquarium. Although dolphins may seem curious, many of their behaviors are often misinterpreted as “friendly” when they actually are, in fact, signs of disturbance or aggression. If a dolphin approaches you in the water, do not engage, pursue, or otherwise interact with the dolphin, and take immediate steps to move away.
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated June 2023