There are two species of spotted dolphins— Atlantic spotted dolphin (Stenella frontalis) and Pantropical spotted dolphin(Stenella attenuata). They are found mostly in the tropics and have a wide variety of habitats, external appearance, and habits. Spotted dolphins are regularly approached by humans in the Bahamas. Their populations in the Pacific have been devastated by tuna fishing. Their spots develop with age. The current population of spotted dolphins is estimated to be 2.2 million.
Atlantic spotted dolphins are found in warm temperate and tropical waters of the Atlantic Ocean. Older members of the species have a very distinctive spots on their bodies. Members of this species in the Bahamas have been observed mating with bottlenose dolphins, which suggests they may be more closely related to the bottlenose dolphins than to other members of the genus Stenella. Studies in the 2020s indicate that this is a consequence of reticulate evolution (such as past hybridization between Stenella (spotted dolphins) and ancestral Tursiops (bottlenose dolphins)) and incomplete lineage sorting, and thus support common bottlenose dolphins truncatus and do-Pacific bottlenose dolphin, which likely explains why Atlantic spotted dolphins can mate with both species of bottlenose dolphins. [Source: Wikipedia]
Pantropical spotted dolphins are found in the Pacific, Atlantic and Indian Oceans, as well as the Persian Gulf and Red Sea while Atlantic Spotted dolphins are limited warm-water regions of the Atlantic. Pantropical spotted dolphins are further divided into two recognized subspecies, the offshore spotted dolphin (Stenella attenuata attenuata), which has a global distribution, and the Coastal spotted dolphin (Stenella attenuata graffmani), which is only found along the Pacific coast of Mexico and Central America. To further complicate matters, these dolphins are closely related to, and sometimes difficult to distinguish from many of the species with which they share their range and often form large mixed species groups. Pantropical spotted dolphins are best known for their longstanding association with the tuna fishing industry in the Eastern Tropical Pacific, which caused significant population declines in the past. [Source: International Whaling Commission]
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
Stenella — Spinner, Spotted and Striped Dolphins
Spotted dolphins belong to the genus Stenella, which also includes spinner 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.
Stenella Dolphin Behavior
Stenella dolphins are nocturnal (active mainly at night), motile (move around as opposed to being stationary), nomadic (move from place to place, generally within a well-defined range), social (associates with others of its species; forms social groups), and 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) /=]
Stenella 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.
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.
Stenella Dolphin Perception and Communication
Stenella dolphins sense using vision, touch, sound, vibrationss, chemicals 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) /=]
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.
Stenella Dolphin Feeding and Predators
Stenella dolphins feed mostly at night on prey from mesopelagic area of the open ocean at depths between 200 meters and 1000 meters. Their prey often migrate vertically towards the surface at night. 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.
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.
Atlantic Spotted Dolphin
Atlantic spotted dolphins (Scientific name: tenella frontalis) are found in the tropical waters of the Atlantic Ocean. They usually form groups of five to 50 individuals but sometimes travel in groups of up to 200. They are fast swimmers and often “surf” in the waves created by vessels. Young Atlantic spotted dolphins do not have spots. As a result, they can look like slender bottlenose dolphins. Their distinctive spotted pattern starts to appear all over their bodies as they get older. Their lifespan is Unknown. [Source: NOAA]
Atlantic spotted dolphins are found in warm temperate, subtropical, and tropical waters throughout the Atlantic Ocean. Their range includes the waters of the U.S. East Coast (Gulf of Mexico to Massachusetts), the Bahamas, Brazil, the Azores and Canary Islands, and Gabon. Warm currents such as the Gulf Stream may affect their distribution. [Source: NOAA]
Atlantic spotted dolphins are found in waters 20 to 250 meters (65 to 820 feet) deep, but are sometimes found in deeper oceanic waters. Along the southeastern and Gulf coasts of the U.S., Atlantic spotted dolphins prefer coastal areas and waters along the continental shelf (the edge of a continent below the ocean’s surface) usually within 250-350 kilometers of the coast. In the Bahamas, the Atlantic spotted dolphin spends most of its time in the shallow water over sand flats. [Source: NOAA, Crystal Allen, Animal Diversity Web (ADW) /=]
Atlantic spotted dolphins eat small fish, invertebrates, and cephalopods (such as squid and octopi). Feeding habits include feeding at or near the surface and "tracking" schools of small fish. Groups of dolphins often coordinate their movements to catch prey together. Individuals sometimes use their beaks to dig into the sand on the ocean bottom to catch hidden fish. Their diet varies with location. In some places they feed primarily on small eels and herring. They have even been known to follow trawlers to eat discarded fish. [Source: NOAA, /=]
The worldwide population of Atlantic spotted dolphins is unknown. Scientists estimate that there are at least 81,000 Atlantic spotted dolphins in U.S. waters. To manage Atlantic spotted dolphins in U.S. waters, the U.S. National Oceanic and Atmospheric Administration has divided them into three stocks: 1) the northern Gulf of Mexico stock, 2) the Puerto Rico and U.S. Virgin Islands stock, and 3) the western North Atlantic stock. Based on the most recent surveys, our scientists estimate that there are about 37,000 dolphins in the northern Gulf of Mexico stock and about 44,000 dolphins in the western North Atlantic stock. The number of dolphins in the Puerto Rico and U.S. Virgin Islands stock is unknown. [Source: NOAA]
Atlantic Spotted Dolphin Characteristics
Atlantic spotted dolphins are 1.5 to 2.3 meters (5 to 7.5 feet) in length and weigh 100 to 143 kilograms (220 to 315 pounds), with an average weight of around 90 kilograms (200 pounds). Females tend to be slightly larger than the males. These dolphins have a robust body with a tall, curved dorsal fin located midway down their back. Their beaks are moderately long. Like other dolphin, their head has a distinctive melon, a rounded forehead that collects sounds from the environment. They have 30 to 42 pairs of small, cone-shaped teeth, 3-5 millimeters in diameter, in each jaw. Atlantic spotted dolphins generally have distally broader rostrum (beak) and fewer but larger teeth than Pantropical spotted dolphins. At times differentiating between these two spotted dolphins is difficult, especially in areas where they converge geographically. [Source: NOAA]
Atlantic spotted dolphins’ color patterns vary with age and location. Young dolphins do not have any spots. Instead, they have a dark gray back with a pale white underside. This lack of spots can make young Atlantic spotted dolphins look like slender bottlenose dolphins. An Atlantic spotted dolphin starts to develop spots after its first birthday. As the dolphin matures, the spots become darker and more widespread, especially on its back.
Atlantic spotted dolphins spots are not present at birth. They and generally do not appear until the onset of weaning. According to Animal Diversity Web: The first spots to appear on the calves are dark spots on the animal's ventral surface. As the dolphin approaches puberty, the ventral spots increase in number and size and pale dorsal spots appear as well. The number of spots continues to increase with age, similar to the development of spotting in Pantropical spotted dolphins. There is a large amount of variation in the adult color pattern, between populations and between individuals. At times some individuals become so heavily spotted that they appear white from a distance. Spotting seems to decrease with the distance from the continental shores of North America. In the Azores some specimens have had few or no ventral spots, but well developed dorsal spotting. [Source: Crystal Allen, Animal Diversity Web (ADW) /=]
The beak of Atlantic spotted dolphins is long and narrow, a typical feature of all Stenella dolphins. Atlantic spotted dolphins are larger in size, but not length, than Pantropical spotted dolphins. Proportionately larger flippers, flukes and dorsal fins are also characteristic of Atlantic spotted dolphins. The skull of the Atlantic spotted dolphin varies in size with individuals and with geographical region. Skull size is generally correlated with body size. /=\
Atlantic Spotted Dolphin Behavior
Atlantic spotted dolphins are motile (move around as opposed to being stationary), social (associates with others of its species; forms social groups) and regarded as highly intelligent. They live in close knit groups called pods of less than 50 individuals but sometimes travel in groups of up to 200. In coastal waters, groups usually consist of five to 15 individuals. Atlantic spotted dolphins pods have complex social organizations with individual recognition and bonding. Within these groups, the dolphins are sometimes organized by age or sex. Atlantic spotted dolphins often school with other species, such as spinner dolphins. Atlantic spotted dolphins are known for coming to the aid of other dolphins in their pod that are in distress. If a member of the group is wounded or sick, the others will take turns supporting it in the water until it recovers or dies. [Source: NOAA]
Atlantic spotted dolphins are active swimmers. They can dive up to 60 meters (200 feet) and have been recorded holding their breath for up to 10 minutes. Most of their dives are less than 10 meters (33 feet) and last for 2 to 6 minutes. Atlantic spotted dolphins are often described as “acrobatic” swimmers, frequently leaping out of the water or jumping at the water’s surface and doing forward flips. They can also swim very quickly and often “surf” in the waves created by vessels. They sometimes interact with other cetacean species, such as bottlenose dolphins.
Atlantic spotted dolphins blow bubbles through their blowholes as one way to communicate with members of their group. They also communicate with sound and have a complex communication system that is made up of narrow-band whistles, clicks, cackling and uttering sharp cries.. These whistles differ enough between individuals that the human ear can distinguish between individual dolphins. If a dolphin is in distress it can call out for help. The dolphin puts out an intermittent distress signal that alerts the other dolphins and they hurry to help it. [Source: Crystal Allen, Animal Diversity Web (ADW) /=]
Pantropical Spotted Dolphins
Pantropical spotted dolphins(Scientific name: Stenella attenuata) are relatively small, reaching lengths of 2.8 to 3.3 meters (6 to 7 feet) and weighing approximately 113 kilograms (250 pounds) at adulthood. They have long, slender snouts or beaks. Like the Atlantic spotted dolphin, pantropical spotted dolphins do not have spots at birth, but accumulate them as they age until they are almost completely covered with overlapping patterns. They are also distinguished by a dark cape or coloration on their backs — stretching from their head to almost midway between the dorsal fin and the tail flukes — and by a white-tipped beak. Their lifespan is 46 years.[Source: NOAA]
Pantropical spotted dolphins can be found in all tropical and subtropical oceans worldwide. Native to the Indian Ocean, Atlantic Ocean and Pacific Ocean, they migrate seasonally to the Japanese coast and are the most common cetacean in the Gulf of Mexico. Although some live inshore, most live offshore, where the temperature of the deeper water remains fairly constant. The depleted northeastern stock inhabits the eastern tropical Pacific Ocean, far at sea. Coastal spotted dolphins are found within 100 miles of the coast
Pantropical spotted dolphins feed mainly on squid and small fish, which they hunt near the ocean surface. These dolphins have also been known to feed on crustaceans such as isopods and pteropods (swimming sea snails). Pantropical spotted dolphins are very social and often school with other dolphin species, including the rough-toothed dolphin, short-finned pilot whale, and spinner dolphins. In the Hawaiian archipelago, there are genetically distinct populations of pantropical spotted dolphins found between Hawaii Island, Maui Nui, Oahu, and offshore. Animals from each population can travel 120 to 300 miles offshore, but they are generally found closer to the islands. The. [Source: NOAA]
Pantropical Spotted Dolphins Physical Characteristics
Pantropical spotted dolphins range in weight from 60 to 165 kilograms (132 to 363 pounds). They are smaller in size, but longer than Atlantic spotted dolphins. They are very fast animal, swimmers, capable of reaching speeds between 22 and 28 kilometers per hour (14 to 17 miles per hour). [Source: Deanna Riseman, Animal Diversity Web (ADW) /=]
Pantropical spotted dolphins obtain more spots as they grow older. Its dorsal surface is dark gray but covered in paler spots, while its paler ventral surface is covered with dark spots. Another distinguishing feature is the spotted dolphin's bright, white snout. It also has melon, a fatty area located on its forehead.
Inshore spotted dolphins tend to be larger than offshore dolphins. Males are generally larger than females, yet females have longer rostra. The spotted dolphin has between 29 and 37 small, rounded teeth on either side of its upper and lower jaws. It has pectoral fins (on the sides), a dorsal fin (on the central back), and tail flukes. The blowhole, used for breathing and communication, is located on the top of the head. Because Pantropical spotted dolphins has a thin layer of blubber, it has small amounts of stored energy, so it eats high energy foods to make up for the low energy. [Source: Deanna Riseman, Animal Diversity Web (ADW) /=]
Pantropical Spotted Dolphins Behavior
Pantropical spotted dolphins are motile (move around as opposed to being stationary), social (associates with others of its species; forms social groups) and sense using touch, vision, echolocation (emitting sound waves and sensing their reflections to determine the location of objects) and chemicals usually detected with smell. They spend most of the day in shallower water between 300 and 1,000 feet deep. At night, they dive into deeper waters to search for prey. They feed primarily on mesopelagic cephalopods and fishes and are commonly sighted with yellowfin tuna. They use echolocation in the dark locate its food. [Source: NOAA]
Pantropical spotted dolphins usually occur in groups of several hundred to 1,000 animals. The offshore schools tend to be larger in number than those of the inshore dolphins. This species often schools with other dolphin species. Although their specific migratory patterns have not been clearly described, they seem to move inshore in the fall and winter months and offshore in the spring. They can be acrobatic and have the ability to leap to great heights.
According to Animal Diversity Web: At the age of two years, young Japanese Pantropical spotted dolphins join pods of other young animals until they achieve sexual maturity. At that time they return to their original pod. Japanese Pantropical spotted dolphins females also have been known to leave their pods during estrous. These two events of age and gender separation do not appear to take place within the tropical Pacific schools.
Spotted Dolphin Mating and Reproduction
Spotted dolphins are viviparous, meaning they give birth to live young that developed in the body of the mother, and engage in year-round breeding. For Pantropical spotted dolphins, the time between births is between 26 and 36 months in the eastern Pacific and approximately 48 months near Japan Breeding season The average number of offspring is one. On average females reach sexual maturity at age 9.8 to 11.1 years. On average males reach sexual maturity at 14.7 years. [Source: Deanna Riseman, Animal Diversity Web (ADW) /=]
Stenella dolphins are polygynandrous (promiscuous), with both males and females having multiple partners. 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) /=]/=\
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.
Pantropical spotted dolphins do not have any particular birthing season, although the number of births does rise in spring and autumn months. The time between births is between 26 and 36 months in the eastern Pacific and approximately 48 months near Japan. The gestation period lasts a little less than a year, and the lactation period can last for 1.5 years or longer. The mean age of sexual maturity for northern offshore female spotted dolphins is estimated to be 11.1 years, which is higher than the estimated age of 9.8 years for southern offshore females. On the other hand, males' average age of sexual maturity is 14.7 years.
For Atlantic spotted dolphins, the gestation period ranges from 11 to 12 months. On average females reach sexual maturity at age nine years and males do so at 12 years. Females give birth to a single calf every 1 to 5 years. Females are generally sexually mature at nine years. Males do not reach sexual maturity unti their 12th year. There is evidence of year round mating, and gestation is between 11 and 12 months long. [Source: Crystal Allen, Animal Diversity Web (ADW) /=]
Spotted Dolphin Offspring
Among spotted dolphins, the pre-fertilization, pre-birth and pre-weaning provisioning and protecting is done by females. There is an extended period of juvenile learning. Among pantropical spotted dolphins, mating and calving occurs year-round. Lactation usually lasts two years, but it can also last for only one year. At 3 to 6 months old, however, calves will begin taking solid food. Calving intervals depend on the population, but they range from 2.5 to 4 years. Maturity occurs around age 11. Among Atlantic spotted dolphins calves are normally born in May and September. [Source: NOAA]
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. 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. There is an extended period of juvenile learning. 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,
The lactation period for spotted dolphins is very long. According to Animal Diversity Web: Occasionally females have been known to lactate during a new pregnancy, and some have also been known to give birth to twins, although this is rare. Mother dolphins feed near the surface so that they don't have to leave their calves. Pregnant females up to age 35 have been discovered. [Source: Deanna Riseman, Animal Diversity Web (ADW) /=]
Lactating females eat significantly more fish than pregnant or normal spotted dolphins. The lactating female's deviation from the norm is presumably because she requires more energy than normal and pregnant dolphins. More protein and also more energy is obtained from eating fish, rather than from eating the same mass of squid. In addition, fish also contain more calcium and phosphorous, which aid in lactation. Lastly, fish have lower water content, which prevents additional water loss in the lactating female since the consumed fish are hypotonic with the sea water.
Spotted Dolphins, Humans and Conservation
Spotted dolphins are still eaten by humans in some places. Pantropical spotted dolphins are hunted for food in Indonesia, the Philippines and other parts of Asia and the Pacific. A few Atlantic spotted dolphins have been hunted and killed in the Caribbean, South America, West Africa, and other offshore islands for food and bait. Besides being used for food, certain parts of its body were used for medicinal purposes. For example, the oil from the liver was used to treat ulcers. [Source: Crystal Allen, Animal Diversity Web (ADW) /=]
Scientists have studied spotted dolphins because they have a high intelligence level. They have been trained to help in underwater salvage operations and have even taken part in military exercises. Researchers in the Bahamas study language with Atlantic spotted dolphins. The cost and complexity of tuna fishing has increased because of regulations designed to lessen the number of dolphins killed captured or killed by fisherman.
Atlantic spotted dolphins are is listed in the Convention of International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendix II,, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. They are listed “ Data Deficient” on the International Union for Conservation of Nature (IUCN) Red List. Like all marine mammals, are protected under the Marine Mammal Protection Act.
Pan tropical spotted dolphins are designated on the IUCN Red List as a species of “Least Concern”. They are listed in CITES Appendix II,, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. The Pacific northeastern offshore stock is considered depleted under the Marine Mammal Protection Act (MMPA).
Because Pantropical spotted dolphins tend to swim with yellowfin tuna, Pacific fishermen use sightings of these dolphins to help them locate their yellowfin tuna targets. The majority of Pantropical spotted dolphins deaths are a consequence of yellowfin tuna fishing operations. The enormous nets used to catch these tuna can unintentionally entangle dolphins as well as fish. Pantropical spotted dolphins is the dolphin species that has been affected to the greatest extent by the tuna fish industry. Between 1985 and 1990, almost 130,000 were killed each year because of the tuna fish catching methods. Thanks to United States government regulations, such as requiring improvements in fishing equipment, this number has decreased substantially by 100,000 deaths per year. Some spotted dolphins are killed intentionally by Japanese fishermen. Between 500 and 2000 spotted dolphins are harvested annually in order to be eaten by the Japanese.
Threats to Spotted Dolphins
One of the main threats to spotted dolphins is becoming entangled or getting caught in fishing gear. Dolphins can become entangled or captured in commercial fishing gear such as gillnets and purse seines. These interactions can cause dolphins to be injured or killed by entanglement in the gear.
Entanglement is particularly threatening to offshore Pantropical spotted dolphins. Some species of tuna are known to aggregate beneath pods of spotted dolphin stocks in the eastern tropical Pacific. This close association led to the fishing practice of encircling a spotted dolphin school to capture the tuna concentrated below. The tuna purse-seine fishery depleted the pantropical spotted dolphin population in the eastern tropical Pacific, and the northeastern offshore stock in the eastern tropical Pacific is considered depleted under the Marine Mammal Protection Act.
Atlantic spotted dolphins sometimes interact with different types of fishing vessels, often following them and eating discarded catch. Underwater noise pollution interrupts the normal behavior of Atlantic spotted dolphins that rely on sound to communicate and echolocate. If loud enough, noise can cause permanent or temporary hearing loss. Noise interference from vessels, as well as industrial and military activities, disturbs Atlantic spotted dolphins’ feeding, communication, and orientation.
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