SPECIES OF DOLPHINS
There are 37 different kinds of dolphin. The most familiar one to humans is the bottlenose dolphin like Flipper and most of the dolphins in dolphin shows. The most numerous are the common dolphin, which have distinctive white and black markings. There are millions of them. They have been observed gathering in large groups and going into a frenzy, perhaps to panic schooling fish.
The Atlantic Humpbacked dolphin is common in coastal waters off West Africa. It is known for cooperating with fisherman to drive fish towards their nets. Atlantic white-side dolphins are often seen off the coast of the United States, sometimes riding the bow waves of humpback and fin whales. Northern right whale dolphins do not have a dorsal fin. They live in the north Pacific and have been observed leaping 23 feet in the air.
In July 2005, the discovery of a new species of dolphin was announced. The Australia snubfin dolphin lives in northern, coastal Australia. It is related to the Irrawaddy dolphin — a river dolphin — but different enough to be declare a new species.
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
Common dolphins (Delphinus delphis) are the most abundant cetacean (whale, dolphin and porpoise) in the world, with a global population of about six million. Despite its name it is not regarded as the archetypal dolphin. That distinction goes to bottlenose dolphin due to its popular appearances in aquariums and the media. However, common dolphins, rather than bottlenose dolphins, are the dolphin species most often depicted in Ancient Greek and Roman art most notably in a mural painted by the ancient-Egyptian-era Greek Minoan civilization. [Source: Wikipedia]
Common dolphins are currently the only member of the genus Delphinus. The common dolphin belongs to the subfamily Delphininae, making this dolphin closely related to the three different species of bottlenose dolphins, humpback dolphins, striped dolphins, spinner dolphins, clymene dolphin, spotted dolphins, fraser's dolphin and the tucuxi and guiana dolphin.
Common dolphins were originally categorized into two different species (now thought to be ecotypes), the short-beaked common dolphin and the long-beaked common dolphin. However, recent evidence has shown that many populations of long-beaked common dolphins around the world are not closely related to one another and are often derived from a short-beaked ancestor and do not always share common derived characteristics. For this reason, they are no longer considered different species. Some sources — such as the NOAA wbesites — still consider them separate species though,
Bottlenose dolphins (Scientific name:Tursiops) are usually gray in color and have a pronounced bottle-shaped snout. Often featured in television shows and movies, they can reach lengths of three meters (10 feet) and weigh as much as 450 kilograms (1,000 pounds). They eat around 13.5 kilograms (30 pounds) of fish a day, mostly pinfish, pigfish and mullet, and come to the surface an average of once every 28 seconds to breath. Female bottlenose dolphins often live into their early 50s, while males typically live between 40 and 45 years. The maximum age recorded in the wild was a 58-year-old female,
bottlenose dolphin Common bottlenose dolphins get their name from their short, thick snout (or rostrum). Fossils of Tursiops have been found in Pliocene Period (5.4 million to 2.4 million years ago) and Pleistocene Period (less than two million years old) deposits. It has been suggested that they originated in the Mediterranean region. Tursiops species are a descendant of terrestrial mammals from the family Pakicetidae, terrestrial whales from the early Eocene (56 million to 33.9 million years ago) as are other dolphins and whales.
Bottlenose dolphins have a long association with humans in regard to entertainment, tourism and research. They have been described in literature dating as far back to ancient Greece and Rome. The first bottlenose dolphins were publicly displayed in 1883 and have been a fixture of oceanarium and marine park shows around the world for a long time. The term Tursiops means dolphin-like. It is derived from the Latin word for dolphin, Tursio, and -ops, which is the Greek suffix for appearance.
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.
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]
Striped dolphins (scientific name: Stenella coeruleoalaba) are among the most abundant and widespread dolphins in the world. They prefer deep tropical to warm temperate oceanic waters, and are attracted to upwelling areas, where deep, cold, nutrient-rich water rises toward the surface. and convergence zones, where ocean currents meet. [Source: NOAA]
Striped dolphins are usually found in tight, cohesive groups of about 25 to 100 individuals and have been observed breaching, jumping, and leaping over 20 feet above the surface of the water. They display a unique behavior called roto-tailing, when the animal leaps high out of the water and vigorously rotates its tail while airborne. Their estimated lifespan is up to 58 years.
Some striped dolphins have been held in captivity, but have not been successfully trained. The second part of their scientific name — “coeruleoalaba” — is derived from the Latin "caeruleus" (sky-blue) and "albus" (white). [Source: Melissa Savage, Animal Diversity Web (ADW) /=]
Striped dolphins are found worldwide and have been observed in the Mediterranean Sea, eastern and western Pacific Ocean, Atlantic Ocean, Indian Ocean, Caribbean Sea, and in the northern Gulf of Mexico. Their range includes waters off Greenland, northern Europe (United Kingdom, Denmark), the Mediterranean Sea, Japan, Argentina, South Africa, western Australia, and New Zealand. In the United States, they can be found off the west coast, in the northwestern Atlantic, and in the Gulf of Mexico. They also live in the waters off Hawaii, but do not live in the colder temperate and boreal waters of Alaska. This species has been documented outside its normal range in areas such as the Faroe Islands, southern Greenland, the Kamchatka Peninsula, and Prince Edward Island. [Source: NOAA]
Risso's dolphins (Scientific name: Grampus griseus) are sometimes called gray dolphins. They are found in the temperate and tropical zones of all the world’s oceans. These cetaceans generally prefers deeper offshore waters, especially near the continental shelf edge and slope, where they can dive to at least 300 meters (1,000 feet) and hold their breath for 30 minutes. They are also very active on the ocean surface. [Source: NOAA]
Risso's dolphins are typically found in groups of between 10 and 30 animals, though they have been reported as solitary individuals, in pairs, or in loose aggregations in the hundreds or thousands. Occasionally, this species associates with other dolphins and whales. They are sometimes considered part of a subfamily referred to as “blackfish,” which also includes false killer whales, pygmy killer whales, melon-headed whales, long-finned pilot whales, and short-finned pilot whales. Risso’s dolphins have an estimated lifespan of at least 35 years.
Risso's dolphins to prey on a mix of near surface, open ocean and bottom-dwelling marine organisms — mainly fish (such as, anchovies), krill, and cephalopods (such as, squid, octopus, and cuttlefish) and crustaceans. One of their most important prey item is the greater argonaut, which is also known as the paper nautilus. Although they are capable of making very deep dives, usually they make shorter dives of just a few minutes. Risso’s dolphins feed mainly at night, when their prey is closer to the surface. Most of their diet consists of squid, and they have been known to move into continental shelf waters when following their preferred prey. They also feed along the continental shelf in waters between 600 and 800 meters deep. [Source: Kelsey Hans, Animal Diversity Web (ADW) /=]
Vaquita Vaquita are the world’s smallest porpoise. There are only around 200 of them left and they all live in the northern reaches of the Gulf of California, Mexico. The gulf, also called the Sea of Cortez, is the thousand-mile-long spear of ocean wedged between the mainland of northwestern Mexico and Baja California. The population of the species is falling at an alarming rate mainly because of accidental entanglement in fishing gear. The animal’s slow maturation and low birthrate compound the problem. [Source: Robert L. Pitman and Lorenzo Rojas-Bracho, Natural History magazine, July -August 2007]
The vaquita was first recognized as a new species in 1958, on the basis of three skulls found on beaches in the northern gulf. But a quarter century passed before a live animal was scientifically documented, and only in 1985 were its external features first described by biologists.
Robert L. Pitman and Lorenzo Rojas-Bracho wrote in Natural History magazine, “Its torpedo-shaped body measures less than five feet from snout to tail; calves are just twenty-eight inches long at birth, the size of a large loaf of bread. From a distance, the vaquita appears drab gray with a lighter belly, but at close range some intriguing details in the paint job emerge. A black stripe runs forward from each flipper to the middle of the lower lip, so the animal appears to be holding its own bridle. It has a black, circular patch around each eye. And its black lips set off a haunting little smile: Mona Lisa with black lipstick.
Pacific white-sided dolphins (Scientific name: Lagenorhynchus obliquidens) are known for the distinct coloring that give them their name, are a playful and highly social marine mammal. They are also sometimes known as the “hookfin porpoise” because of their large, curved dorsal fin, though they are not technically porpoises. Pacific white-sided dolphins can be seen travelling in schools of thousands, but group sizes are usually between 10 and 100 animals. These extremely playful dolphins are often seen “bow riding” (swimming near the front part of a ship) and jumping, somersaulting, or even spinning in the air. Their lifespan is 36 to 40 years. Some live longer than that. [Source: NOAA]
Atlantic white-sided dolphins (Scientific name: Lagenorhynchus acutus) are found in the temperate waters of the North Atlantic. In the United States, they are found off the coast of North Carolina to Maine. They are named after their distinctive yellowish-tan streak on their sides. They weigh 136 to 181 kilograms (400 to 500 pounds) and reach lengths of up 2.7 meters (nine feet). Their lifespan is about 25 years.
Pacific white-sided dolphins are pelagic, meaning they live in the open ocean and nearshore waters, but are unlikely to be found close to shore. They live in the temperate waters of the North Pacific Ocean. In the United States, they are found off the coast of California, Oregon, Washington, and Alaska. Worldwide, they are found in the southern Bering Sea (around the Aleutian Islands), Sea of Okhotsk, Sea of Japan, and Yellow and East China Seas to the south of Japan. In all, there are three stocks of Pacific white-sided dolphins in U.S. waters. Population trends for the North Pacific stock off the coast of Alaska are unknown. A survey of the two stocks off the coasts of Washington, Oregon, and California from 2008 to 2014 found a population of more than 21,000 dolphins.
Adult Pacific white-sided dolphins are 1.7 to 2.4 meters (5.5 to 8 feet) in length and weigh 136 to 181 kilograms (300 to 400 pounds). They have have a robust body, short rostrum (snout), and large dorsal fin compared to their overall body size. Their back, fluke (tail), and lips are black; their sides, dorsal fin, and flippers are gray; and their belly is white. They have a white or light gray stripe along their sides that extends from the eye to the tail, sometimes referred to as "suspenders." Males are generally larger than females. Pacific white-sided dolphins are most likely to be confused with common dolphins and Dall’s porpoises because they have similar large light-colored flank patches.
Pacific white-sided dolphins feed on a variety of prey, such as squid and small schooling fish (capelin, sardines, and herring). They can dive underwater for more than 6 minutes to feed. They have small conical teeth that help them catch and hold on to their prey; each tooth row contains 23 to 36 pairs of teeth. Instead of using their teeth to chew their food, dolphins use their teeth to grip food before swallowing it whole — head first — so the spines of the fish do not catch in their throats. Pacific white-sided dolphins often work together as a group to herd schools of fish. Each adult eats about 20 pounds of food a day.
Males reach sexual maturity around 10 years and females around 8 to 11. They mate and give birth from late spring to fall, except in the central Pacific, where calves are born in late winter to spring. Gestation is usually nine to 12 months, and calves weigh about 30 pounds at birth and are about 3 to 4 feet. Mothers nurse their calves for up to 18 months. Females usually give birth every 3 years.
Threats to White-Sided Dolphins
The worldwide population of Atlantic white-sided dolphins is unknown, but scientists estimate that there are at least 300,000 of them, with about are about 93,000 dolphins in the western North Atlantic stock. During the 1970s and 1980s in the northwestern Atlantic Ocean, this species population significantly increased due to changes in prey.
Pacific white-sided dolphins are not endangered or threatened The Convention on International Trade in Endangered Species (CITES) places both the Atlantic and Pacific white-sided dolphins in Appendix II, which lists species not necessarily threatened with extinction now but may become so unless trade is closely controlled. Both are protected by the Marine Mammal Protection Act (MMPA) throughout their range.
Threats include entanglement in fishing gear and ocean noise Low-frequency underwater noise pollution can interrupt the normal behavior of Pacific white-sided dolphins. Noise interference hinders their ability to use sound, which in turn disturbs their ability to communicate, choose mates, find food, avoid predators, and navigate. [Source: NOAA]
One of the main threats to the Pacific white-sided dolphin is getting caught in fishing gear. Dolphins can become entangled or captured in commercial fishing gear such as gillnets, seines, trawls, trap pots, and longlines. Before a 1933 United Nations moratorium that banned large-scale drift nets, Pacific white-sided dolphins were often captured by Japanese fisheries. In addition, every year between 1978 and 1991, thousands of Pacific white-sided dolphins suffered mortality and serious injury when caught incidentally in high-seas fisheries for salmon and squid. These fisheries were closed in 1991 and no other large-scale fisheries have operated in the central North Pacific since 1991.
Atlantic white-sided dolphins have been incidentally taken in fisheries such as driftnets, gillnets, and trawls in the Atlantic Ocean. In waters off of Ireland, significant numbers of these dolphins have been incidentally caught in mid-water trawls. They have been directly hunted and killed for food and oil in the drive fisheries of the Faroe Islands, Greenland, Newfoundland (Canada), and Norway.
Rough-toothed dolphin Rough-toothed dolphins (Scientific name: Steno bredanensis) are found around the world. They are usually found in tight-knit groups of 10 to 20 individuals but have been reported in groups of up to 100 individuals. They often associate with other cetacean species, including short-finned pilot whales, bottlenose dolphins, pantropical spotted dolphins, and spinner dolphins. They eat squids and different types of fish. Rough-toothed dolphins can remain underwater for up to 15 minutes. They can also adapt well to captivity, which is unusual for oceanic dolphins. [Source: NOAA]
Rough-toothed dolphins are generally found in deep oceanic waters in tropical and warmer temperate areas in the Atlantic, Indian, and Pacific Oceans from 40° north to 35° south latitude. They prefer areas with lots of available prey. Rough-toothed dolphins become sexually mature at 10 to 14 years of age and can live for up to 36 or more years.
Rough-toothed dolphins are relatively small compared to other dolphins. They can reach up to 2.6 meters (8.5 feet) in length and weigh about 160 kilograms (350 pounds). They have a small head with a long beak, and no demarcation between their gently sloping melon (or forehead) and beak. Their dorsal fin and flippers are fairly long. They have a “reptilian” appearance that is unique among dolphins. Rough-toothed dolphins have dark gray bodies with a white throat and “lips.” They also have a narrow dark cape that runs down their back between the blowhole and dorsal fin. Their underside usually has some white or lighter spots or blotches.
The worldwide population of rough-toothed dolphins is unknown. In U.S. waters, there are three stocks: the Hawaiian stock, the northern Gulf of Mexico stock, and the western North Atlantic stock. NOAA estimates that there are about 6,000 dolphins in the Hawaiian stock, 600 dolphins in the northern Gulf of Mexico stock, and 300 dolphins in the western North Atlantic stock — for a total of about 6,900 rough-toothed dolphins in U.S. waters. CITES places them in Appendix II. They are protected by the MMPA throughout their range. Threats include entanglement in fishing gear and ocean noise. Rough-toothed dolphins have been killed in direct fisheries in Japan, Sri Lanka, Indonesia, Papua New Guinea, the Solomon Islands, West Africa, and the Caribbean Sea.
White-beaked dolphins (Scientific name: Lagenorhynchus albirostris) are generally found in colder temperate and subpolar waters in the North Atlantic Ocean. They are active swimmers and often “surf” the waves created by vessels. They are usually found in groups of five to 30 individuals but sometimes travel in groups of up to 1,500. White-beaked dolphins hunt for food both near the water’s surface and along the ocean bottom. Some fishermen in Canada call these dolphins “squidhounds” because they eat squid and octopi. [Source: NOAA]
The range of white-beaked dolphins includes the waters of eastern North America (Massachusetts to Newfoundland), northern Europe, Scandinavia, Greenland, the United Kingdom, and the Barents Sea. They prefer waters less than 200 meters (650 feet) deep. The distribution of this species varies with the seasons. Most white-beaked dolphins move south and farther offshore during the winter months. They then return north and closer to shore once the ice recedes during the warmer summer months.
White-beaked dolphins are relatively large dolphins. They are about 2.4 to 3 meters (8 to 10.5 feet) long and weigh 180 to 350 kilograms (395 to 770 pounds). Males are usually larger than females. Both males and females have a streamlined, robust body with a small beak and a large, tall, curved dorsal fin. Their body is mostly dark gray or black on the upper sides and back with light gray or white patches on their sides, back, and underside. The dorsal fin, flippers, and flukes are mostly dark. Their beaks, which are very short and thick, also have white “lips.” White-beaked dolphins have 22 to 28 pairs of small, cone-shaped teeth in each jaw.
White-beaked dolphin groups can be organized by age and sex. These dolphins are sometimes seen in groups with other species, such as fin whales, humpback whales, and other small dolphins such as bottlenose and Atlantic white-sided dolphins. White-beaked dolphins are active swimmers. They often breach and jump at the water’s surface. They eat schooling fish (such as, haddock, cod, and herring), crustaceans (such as, shrimp and crabs), and cephalopods (such as, squid and octopi). They typically work together to catch fish at the water’s surface but will also feed along the ocean bottom. They reach sexual maturity when they are 7 to 12 years old. Females are pregnant for about 11 months and give birth to a single calf, usually between May and September. Calves are about 1.2 meters (4 feet) long and weigh about 40 kilograms (90 pounds) at birth.
The worldwide population of white-beaked dolphins is unknown. In U.S. waters, about 2,000 dolphins make up the western North Atlantic stock. CITES places white-beaked dolphins 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 the MMPA. Threats include entanglement in fishing gear and ocean noise. White-beaked dolphins are sometimes targeted and hunted for meat and oil in waters off Canada (Labrador and Newfoundland), Greenland, Iceland, and Norway. [Source: NOAA]
Dusky dolphins (Scientific name: Lagenorhynchus obscurus) live the Southern Hemisphere. They can be found near the coasts of South America, South Africa, Kerguelen Islands in the southern Indian Ocean, South Australia and New Zealand. They are usually found in warm to cool temperate waters and are particularly associated with New Zealand. They are acrobatic, curious and easy to approach. They are known for their displays — turning, jumping and charging line-abreast formations near ships. Swimming with these dolphins has became a major tourist attraction. In Kaikoura, New Zealand, there is a lucrative dolphin-watching and swimming with dolphins tourism industry centered around these animals. [Source: Helen Yu, Animal Diversity Web (ADW) /=]
The main prey species of dusky dolphins are anchovies, squid and schooling shrimp. Dusky dolphins feed near the surface, deep in the water column and at or near the sea bottom. Groups with 3000 or more individuals engage in cooperative herding of large schools of small fish. Dusky dolphins have been recorded swimming with schools of Common Dolphins, and even mating with them
Dusky dolphins are classified as "data deficient" on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. They are not considered endangered or threatened but hundreds, maybe thousands of dusky dolphins have been killed annually by the small-cetacean fishery in Peru and as bycatch by anchovy fisherman. In 1990 the Peruvian government banned the direct fishery for small cetaceans, but the ban has not been very effective. After the ban was put in place one could buy fresh dusky dolphins meat in Lima markets for US$1-1.25 per kilograms. Nearly 10,000 of these dolphins were killed each year in the 1970s. Orcas (killer whales) prey on dusky dolphins.
Dusky Dolphin Characteristics, Behavior and Reproduction
Dusky dolphins are a medium-sized dolphin that reach 1.8 meters to 2 meters (6 to 6.5 feet) in length as adults. Their head slopes evenly down from the blowhole to the tip of the snout and they have virtually no beak. According to Animal Diversity Web: The tip of the dorsal fin is rather blunt and is not markedly hooked. These dolphins have a bluish-black tail and back. A dark band runs diagonally across the flanks from below the dorsal fin towards the vent and along the tailstock. The underside of the body is white, and whitish-grey color extends over the flanks. The tips of the snout and lower jaw are dark. A grey area extends from the eye down to the flipper. Two diagonal whitish streaks run forward from tail up past the base of dorsal fin. There are 24-36 pairs of small, pointed teeth about 3 millimeters in diameter in each jaws. The upper jaw usually has two less teeth than the lower. [Source: Helen Yu, Animal Diversity Web (ADW) /=]
dusky dolphin Dusky dolphins are diurnal (active mainly during the daytime), motile (move around as opposed to being stationary) and social (associates with others of its species; forms social groups). They are often seen in groups of 6-15, occasionally up to 300 for feeding aggregations. Groups are a mixture of ages and include members of both sexes. Groups are usually stable for at least several days. Dusky dolphins are among the most altruistic of the dolphins. They have been reported to assist other dolphin species in distress, and to aid humans. Dusky dolphins are extremely fond of playing and leaping; they often leap in schools. Dusky dolphins are especially attracted to boats. They are fast swimmers, reaching speeds up to 40 kilometers per hour (23 miles per hour).
Dusky dolphins spend night-time in small schools no more than a kilometer offshore. During this period, they rest, with only slow movements. In the morning, they move into deeper water, about two to ten kilometers from shore. At this time, they search for food in groups, swimming in a line abreast with each animal 10 meters from the next. Then they may aggregate up to 300 for cooperative herding. By mid-afternoon, feeding may be concentrated in one area. At this time they also start to interact socially in play and sexual activity. In the evening, the large school of dusky dolphins splits up into smaller groups and returns inshore.
Dusky dolphins produce a variety of whistles, squeaks, squeals and clicks. These sounds are loud and directional. The sound of a dusky dolphin reentering the water after a leap carries at least 500 meters but less than 1km underwater. In air, the sound can be heard as far away as 3-km distance. Dusky dolphins often leap before and after feeding. The leap has been hypothesized to function to recruit other dolphins to assist in feeding activities (Herman 1980). /=\
Dusky dolphins are viviparous, meaning they give birth to live young that developed in the body of the mother, and engage in seasonal breeding. Mating usually takes place during spring, with the average number of offspring being one, and the peak months for birth being June to August.. The average gestation period is 11 months. The average weaning age is 18 months. Dusky dolphins are polygynandrous (promiscuous), with both males and females having multiple partners. Adult males compete for mating access with females. Pair bonds do not appear to be formed, but social cohesion within the school seems strong. Calves weigh about five kilograms (11 pounds) at birth. /=\
Fraser's dolphins (Scientific name: Lagenodelphis hosei) are found in warm, temperate, subtropical, and tropical waters around the world. They are active swimmers and sometimes found in large groups with hundreds of individuals. They are named after Francis Fraser, a scientist from the British Museum, who first described this species in 1956 based on a skull found on a beach in Borneo. It was not until 1971, however, that scientists first documented Fraser’s dolphins in the wild. While the worldwide population of Fraser's dolphins is unknown, scientists estimate that at least 100,000 to 289,000 of them live in the eastern tropical Pacific Ocean. Fraser’s dolphins have lifespan of about 18 years or maybe more.[Source: NOAA]
Fraser's dolphins are native to the Indian Ocean, Atlantic Ocean and Pacific Ocean. They prefer to live in deep waters (3,300 feet deep) and are often found in areas of upwelling (areas where cold, nutrient-rich water rises toward the surface). They also live near coastlines or where the continental shelf (the edge of a continent below the ocean’s surface) is narrow. In U.S. waters, there are three stocks: the Hawaiian stock, the northern Gulf of Mexico stock, and the western North Atlantic stock. The the Hawaiian stock is estimated to have about 10,000 dolphins. Numbers in the Gulf of Mexico and western North Atlantic stocks are unknown. Stranded Fraser's dolphins have sometimes been reported in places outside of their typical range, such as southern Australia, France, western Scotland, and Uruguay.
Fraser’s dolphins are 1.8 to 2.7 meters (6 to 9 feet) in length and weigh 160 to 200 kilograms (350 to 450 pounds). They have a stocky body with a small, distinct beak. Their dorsal fin — located midway down their back — is small and triangle-shaped. Their flippers and flukes are smaller than those of other dolphin species. Males are slightly longer and heavier than females. They also have more distinct color patterns. All Fraser's dolphins have a dark stripe that extends down their side from eye to flipper. This stripe reminds some people of a raccoon or "bandit" mask. The exact shape of the stripe varies based on geography and sex. Their upper body is a bluish or brownish-gray, while their underside is usually pale white or pink. Calves are usually less colorful than adults. There is no sexual dimorphism (differences between males and females): except in the size and shape of the dorsal-fin, with male fins being larger than female fins. [Source: NOAA]
Fraser's dolphins feed on deep-sea fish, crustaceans (such as shrimp), and cephalopods (such as squid and octopus). They have 20 to 44 pairs of small, cone-shaped teeth to help them catch prey and can dive up to 610 meters (2,000 feet) to get food. There is strong evidence that they prefer to feed at depths of 250 to 500 meters (820 to 1640 feet) and rarely at the surface. No predation on this species has been observed, but killer whales, false killer whales and sharks probably occasionally take these dolphins as prey. [Source: Bret Weinstein, Animal Diverssity Web (ADW)]
Fraser’s dolphin’s are not regarded as endangered or threatened. The International Union for Conservation of Nature (IUCN) Red List classifies them as a species of “Least Concern”. Convention on International Trade in Endangered Species (CITES) places them in Appendix II, which lists species not necessarily threatened with extinction now but may become so unless trade is closely controlled. Fraser’s dolphins, like all marine mammals, are protected under the Marine Mammal Protection Act (MMPA). Threats include interactions with fishing gear and hunting for oil and meat in Indonesia, Japan, the Lesser Antilles of the Caribbean, the Philippines, and Sri Lanka. Because they do not feed at the surface, Fraser’s dolphin’s do not compete with fisherman for tuna or other pelagic (open ocean) fish. Even so they can become entangled or captured in commercial fishing gear such as gillnets, seines, trawls, trap pots, and longlines. Specifically, they have been caught in tuna purse seine fisheries in the eastern tropical Pacific and the Philippines. These interactions can injure dolphins or kill them by entanglement in the gear.
Fraser’s Dolphin Behavior and Reproduction
Fraser's dolphin Fraser's dolphins are motile (move around as opposed to being stationary) and social (associates with others of its species; forms social groups). They are usually found in large, tight groups of 10 to 100 individuals, but they have sometimes been seen in groups of up to 1,000 individuals. They are also sometimes seen in mixed groups with related species such as false killer whales, melon-headed whales, Risso's dolphins, and short-finned pilot whales. [Source: NOAA]
Fraser’s dolphins are aggressive and splashy swimmers creating a distinctive spray of water. Groups of individuals sometimes swim in long "chorus line” formations. Fraser's dolphins in some parts of the world are shy and hard to find, while those living in other area are friendly and curious when interacting with vessels. When fleeing from ships, these dolphins can reach speeds of 28 kilometers per hour (18 miles per hour).[Source: NOAA]
Fraser’s dolphins give birth to live young and engage in year-round breeding, with possible peaks in the summer months. The average number of offspring is one one. The average gestation period is 11 months. Fraser’s dolphins become sexually mature when they are 5 to 10 years old (females at 5 to 8 years, males at 7 to 10 years). Females are pregnant for about 10 to 12.5 months and give birth to a single calf every 2 years, usually between spring and autumn. [Source: NOAA; [Source: Bret Weinstein, Animal Diverssity Web (ADW)]
There are four generally recognized species of freshwater dolphin. The Irrawaddy fresh water dolphin is found in the Mekong River in Laos and Cambodia, the Mahakam River in Kalimantan in Indonesia, and the Yangtze in China. They were once found in the Chao Praya River, which flows through Bangkok, but haven't been seen there in decades (See Laos). The three other live in the Ganges in India, the Indus in Pakistan and the Amazon in South America.
Image Source: 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