![Tursiops truncatus 01](https://upload.wikimedia.org/wikipedia/commons/1/10/Tursiops_truncatus_01.jpg)
A dolphin is an
aquatic mammal
Aquatic and semiaquatic mammals are a diverse group of mammals that dwell partly or entirely in bodies of water. They include the various marine mammals who dwell in oceans, as well as various freshwater species, such as the European otter. Th ...
within the
infraorder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
Cetacea
Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...
. Dolphin species belong to the families
Delphinidae
Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as the ...
(the oceanic dolphins),
Platanistidae (the Indian
river dolphin
River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant riv ...
s),
Iniidae
Iniidae is a family of river dolphins containing one living genus, ''Inia'', and four extinct genera. The extant genus inhabits the river basins of South America, but the family formerly had a wider presence across the Atlantic Ocean.
Iniidae a ...
(the New World river dolphins),
Pontoporiidae (the
brackish
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...
dolphins), and the extinct
Lipotidae
Lipotidae is a family of river dolphins containing the possibly extinct baiji of China and the fossil genus ''Parapontoporia'' from the Late Miocene and Pliocene of the Pacific coast of North America. The genus '' Prolipotes'', which is based on ...
(baiji or Chinese river dolphin). There are 40
extant species
Neontology is a part of biology that, in contrast to paleontology, deals with living (or, more generally, ''recent'') organisms. It is the study of extant taxa (singular: extant taxon): taxa (such as species, genera and families) with members st ...
named as dolphins.
Dolphins range in size from the and
Maui's dolphin to the and
orca
The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only Extant taxon, extant species in the genus ''Orcinus'' and is recognizable by its black ...
. Various species of dolphins exhibit
sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
where the males are larger than females. They have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as
seal
Seal may refer to any of the following:
Common uses
* Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly:
** Earless seal, or "true seal"
** Fur seal
* Seal (emblem), a device to impr ...
s, some dolphins can briefly travel at speeds of per hour or leap about . Dolphins use their conical teeth to capture fast-moving
prey
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
. They have well-developed hearing which is adapted for both air and water. It is so well developed that some can survive even if they are blind. Some species are well adapted for diving to great depths. They have a layer of fat, or
blubber
Blubber is a thick layer of vascularized adipose tissue under the skin of all cetaceans, pinnipeds, penguins, and sirenians.
Description
Lipid-rich, collagen fiber-laced blubber comprises the hypodermis and covers the whole body, except for pa ...
, under the skin to keep warm in the cold water.
Dolphins are widespread. Most species prefer the warm waters of the tropic zones, but some, such as the
right whale dolphin
Right whale dolphins are cetaceans belonging to the genus ''Lissodelphis''. It contains the northern right whale dolphin (''Lissodelphis borealis'') and the southern right whale dolphin (''Lissodelphis peronii''). These cetaceans are predominant ...
, prefer colder climates. Dolphins feed largely on fish and squid, but a few, such as the orca, feed on large mammals such as seals. Male dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them. Mothers of some species fast and nurse their young for a relatively long period of time. Dolphins produce a variety of vocalizations, usually in the form of clicks and whistles.
Dolphins are sometimes hunted in places such as Japan, in an activity known as
dolphin drive hunting
Dolphin drive hunting, also called dolphin drive fishing, is a method of hunting dolphins and occasionally other small cetaceans by driving them together with boats and then usually into a bay or onto a beach. Their escape is prevented by closing ...
. Besides drive hunting, they also face threats from
bycatch
Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...
, habitat loss, and
marine pollution
Marine pollution occurs when substances used or spread by humans, such as industrial waste, industrial, agricultural pollution, agricultural and municipal solid waste, residential waste, particle (ecology), particles, noise, excess carbon dioxid ...
. Dolphins have been depicted in various cultures worldwide. Dolphins are sometimes kept in captivity and trained to perform tricks. The most common dolphin species in captivity is the
bottlenose dolphin
Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the common ...
, while there are around 60
orcas in captivity.
Etymology
The name is originally from
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
(''delphís''), "dolphin",
which was related to the Greek (''delphus''), "womb".
[ The animal's name can therefore be interpreted as meaning "a 'fish' with a womb". The name was transmitted via the ]Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''delphinus'' (the romanization
Romanization or romanisation, in linguistics, is the conversion of text from a different writing system to the Roman (Latin) script, or a system for doing so. Methods of romanization include transliteration, for representing written text, and ...
of the later Greek δελφῖνος – ''delphinos''[), which in ]Medieval Latin
Medieval Latin was the form of Literary Latin used in Roman Catholic Western Europe during the Middle Ages. In this region it served as the primary written language, though local languages were also written to varying degrees. Latin functioned ...
became and in Old French
Old French (, , ; Modern French: ) was the language spoken in most of the northern half of France from approximately the 8th to the 14th centuries. Rather than a unified language, Old French was a linkage of Romance dialects, mutually intelligib ...
''daulphin'', which reintroduced the ''ph'' into the word "Dolphin". The term mereswine (that is, "sea pig") has also historically been used.
The term 'dolphin' can be used to refer to most species in the family Delphinidae
Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as the ...
(oceanic dolphins) and the river dolphin families Iniidae
Iniidae is a family of river dolphins containing one living genus, ''Inia'', and four extinct genera. The extant genus inhabits the river basins of South America, but the family formerly had a wider presence across the Atlantic Ocean.
Iniidae a ...
(South American river dolphins), Pontoporiidae (La Plata dolphin
The La Plata dolphin, franciscana or toninha (''Pontoporia blainvillei'') is a species of dolphin found in coastal Atlantic waters of southeastern South America. It is a member of the river dolphin group and the only one that lives in the ocean ...
), Lipotidae
Lipotidae is a family of river dolphins containing the possibly extinct baiji of China and the fossil genus ''Parapontoporia'' from the Late Miocene and Pliocene of the Pacific coast of North America. The genus '' Prolipotes'', which is based on ...
(Yangtze river dolphin) and Platanistidae (Ganges river dolphin and Indus river dolphin).
This term has often been applied in the US, mainly in the fishing industry, to all small cetacea
Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...
ns (dolphins and porpoise
Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals an ...
s) are considered to be porpoises, while the fish ''dorado
Dorado () is a constellation in the southern sky. It was named in the late 16th century and is now one of the 88 modern constellations. Its name refers to the dolphinfish (''Coryphaena hippurus''), which is known as ''dorado'' in Spanish, altho ...
'' is called dolphin fish. In common usage the term 'whale' is used only for the larger cetacean species, while the smaller ones with a beaked or longer nose are considered 'dolphins'. The name 'dolphin' is used casually as a synonym for bottlenose dolphin
Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the common ...
, the most common and familiar species of dolphin. There are six species of dolphins commonly thought of as whales, collectively known as blackfish: the orca
The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only Extant taxon, extant species in the genus ''Orcinus'' and is recognizable by its black ...
, the melon-headed whale
The melon-headed whale (''Peponocephala electra''), also known less commonly as the electra dolphin, little killer whale, or many-toothed blackfish, is a toothed whale of the oceanic dolphin family (Delphinidae). The common name is derived from t ...
, the pygmy killer whale
The pygmy killer whale (''Feresa attenuata'') is a poorly known and rarely seen oceanic dolphin. It is the only species in the genus ''Feresa''. It derives its common name from sharing some physical characteristics with the orca also known as t ...
, the false killer whale
The false killer whale (''Pseudorca crassidens'') is a species of oceanic dolphin that is the only extant representative of the genus ''Pseudorca''. It is found in oceans worldwide but mainly in tropical regions. It was first described in 1846 ...
, and the two species of pilot whale
Pilot whales are cetaceans belonging to the genus ''Globicephala''. The two extant species are the long-finned pilot whale (''G. melas'') and the short-finned pilot whale (''G. macrorhynchus''). The two are not readily distinguishable at sea, a ...
s, all of which are classified under the family Delphinidae and qualify as dolphins. Although the terms 'dolphin' and 'porpoise' are sometimes used interchangeably, 'porpoise' usually refers to the Phocoenidae family, which have a shorter beak and spade-shaped teeth and differ in their behavior.
A group of dolphins is called a "school" or a "pod". Male dolphins are called "bulls", females called "cows" and young dolphins are called "calves".
Hybridization
In 1933, three hybrid dolphins beached off the Irish coast; they were hybrids between Risso's and bottlenose dolphins. This mating was later repeated in captivity, producing a hybrid calf. In captivity, a bottlenose and a rough-toothed dolphin
The rough-toothed dolphin (''Steno bredanensis'') is a species of dolphin that can be found in deep warm and tropical waters around the world.
The species was first described by Georges Cuvier in 1823. The genus name ''Steno'', of which this spe ...
produced hybrid offspring. A common-bottlenose hybrid lives at SeaWorld
SeaWorld is an American theme park chain with headquarters in Orlando, Florida. It is a proprietor of marine mammal parks, oceanariums, animal theme parks, and rehabilitation centers owned by SeaWorld Parks & Entertainment (one park will be ...
California. Other dolphin hybrids live in captivity around the world or have been reported in the wild, such as a bottlenose- Atlantic spotted hybrid. The best known hybrid is the wholphin
A wholphin (portmanteau of whale + dolphin) is an extremely rare cetacean hybrid born from a mating of a female common bottlenose dolphin (''Tursiops truncatus'') with a male false killer whale (''Pseudorca crassidens''). The name implies a hy ...
, a false killer whale-bottlenose dolphin hybrid. The wolphin is a fertile hybrid. Two wolphins currently live at the Sea Life Park
Sea Life Park Hawaii is a marine mammal park, bird sanctuary and aquarium in Waimānalo near Makapuʻu Point, north of Hanauma Bay on the island of Oahu in Hawaii, United States. The park first opened in 1964, and includes exhibits that let visi ...
in Hawaii; the first was born in 1985 from a male false killer whale and a female bottlenose. Wolphins have also been observed in the wild.
Evolution
Dolphins are descendants of land-dwelling mammals of the artiodactyl
The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...
order (even-toed ungulates). They are related to the ''Indohyus
''Indohyus'' is an extinct genus of digitigrade artiodactyls known from Eocene fossils in Asia. This small chevrotain-like animal found in the Himalayas is one of the earliest known non-cetacean ancestors of whales.
Discovery
The fossils were di ...
'', an extinct chevrotain
Chevrotains, or mouse-deer, are small even-toed ungulates that make up the family Tragulidae, the only extant members of the infraorder Tragulina. The 10 extant species are placed in three genera, but several species also are known only ...
-like ungulate, from which they split approximately 48 million years ago.
The primitive cetaceans, or archaeocetes
Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean radiation, they include the initial ...
, first took to the sea approximately 49 million years ago and became fully aquatic by 5–10 million years later.
Archaeoceti
Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean radiation, they include the initia ...
is a parvorder comprising ancient whales. These ancient whales are the predecessors of modern whales, stretching back to their first ancestor that spent their lives near (rarely in) the water. Likewise, the archaeocetes can be anywhere from near fully terrestrial, to semi-aquatic to fully aquatic, but what defines an archaeocete is the presence of visible legs or asymmetrical teeth. Their features became adapted for living in the marine environment
Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea (the term ''marine'' comes from the Latin ''mare'', meaning sea or ocean). A habitat is an ecological or environmental ...
. Major anatomical changes include the hearing set-up that channeled vibrations from the jaw to the earbone which occurred with ''Ambulocetus
''Ambulocetus'' (Latin ''ambulare'' "to walk" + ''cetus'' "whale") is a genus of early amphibious cetacean from the Kuldana Formation in Pakistan, roughly 48 or 47 million years ago during the Early Eocene (Lutetian). It contains one species, ' ...
'' 49 million years ago, a streamlining of the body and the growth of flukes on the tail which occurred around 43 million years ago with ''Protocetus
''Protocetus atavus'' ("first whale") is an extinct species of primitive cetacean from Egypt. It lived during the middle Eocene period 45 million years ago. The first discovered protocetid, ''Protocetus atavus'' was described by based on a cran ...
'', the migration of the nasal openings toward the top of the cranium
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
and the modification of the forelimbs into flippers which occurred with ''Basilosaurus
''Basilosaurus'' (meaning "king lizard") is a genus of large, predatory, prehistoric archaeocete whale from the late Eocene, approximately 41.3 to 33.9 million years ago (mya). First described in 1834, it was the first archaeocete and prehistori ...
'' 35 million years ago, and the shrinking and eventual disappearance of the hind limbs which took place with the first odontocetes and mysticetes 34 million years ago. The modern dolphin skeleton
A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
has two small, rod-shaped pelvic bones thought to be vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
hind limbs. In October 2006, an unusual bottlenose dolphin was captured in Japan; it had small fin
A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...
s on each side of its genital slit, which scientists believe to be an unusually pronounced development of these vestigial hind limbs.
Today, the closest living relatives of cetaceans are the hippopotamus
The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extan ...
es; these share a semi-aquatic ancestor that branched off from other artiodactyls some 60 million years ago. Around 40 million years ago, a common ancestor between the two branched off into cetacea and anthracotheres
Anthracotheriidae is a paraphyletic family of extinct, hippopotamus-like artiodactyl ungulates related to hippopotamuses and whales. The oldest genus, ''Elomeryx'', first appeared during the middle Eocene in Asia. They thrived in Africa and Euras ...
; anthracotheres became extinct at the end of the Pleistocene two-and-a-half million years ago, eventually leaving only one surviving lineage: the two species of hippo.
Anatomy
Dolphins have torpedo-shaped bodies with generally non-flexible necks, limbs modified into flippers, a tail fin, and bulbous heads. Dolphin skulls have small eye orbits, long snouts, and eyes placed on the sides of its head; they lack external ear flaps. Dolphins range in size from the long and Maui's dolphin to the and orca
The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only Extant taxon, extant species in the genus ''Orcinus'' and is recognizable by its black ...
. Overall, they tend to be dwarfed by other Cetartiodactyl
The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...
s. Several species have female-biased sexual dimorphism, with the females being larger than the males.
Dolphins have conical teeth, as opposed to porpoise
Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals an ...
s' spade-shaped teeth. These conical teeth are used to catch swift prey such as fish, squid or large mammals, such as seal.
Breathing involves expelling stale air from their blowhole, in an upward blast, which may be visible in cold air, followed by inhaling fresh air into the lungs. Dolphins have rather small, unidentifiable spouts.
All dolphins have a thick layer of blubber
Blubber is a thick layer of vascularized adipose tissue under the skin of all cetaceans, pinnipeds, penguins, and sirenians.
Description
Lipid-rich, collagen fiber-laced blubber comprises the hypodermis and covers the whole body, except for pa ...
, thickness varying on climate. This blubber can help with buoyancy, protection to some extent as predators would have a hard time getting through a thick layer of fat, and energy for leaner times; the primary usage for blubber is insulation from the harsh climate. Calves, generally, are born with a thin layer of blubber, which develops at different paces depending on the habitat.
Dolphins have a two-chambered stomach that is similar in structure to terrestrial carnivores. They have fundic
The gastric glands are glands in the lining of the stomach that play an essential role in the process of digestion. All of the glands have mucus-secreting foveolar cells. Mucus lines the entire stomach, and protects the stomach lining from the e ...
and pyloric
The pylorus ( or ), or pyloric part, connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pylori ...
chambers.
Dolphins' reproductive organs are located inside the body, with genital slits on the ventral (belly) side. Males have two slits, one concealing the penis
A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males do n ...
and one further behind for the anus
The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...
. Females have one genital slit, housing the vagina
In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
and the anus, with a mammary slit on either side.
Integumentary system
The integumentary system is an organ system mostly consisted of skin, hair, nails and endocrine glands. The skin of dolphins is very important as it is specialized to satisfy specific requirements. Some of these requirements include protection, fat storage, heat regulation, and sensory perception. The skin of a dolphin is made up of two parts: the epidermis and the blubber, which consists of two layers including the dermis and subcutis.
The dolphin's skin is known to have a smooth rubber texture and is without hair and glands, except mammary glands. At birth, a newborn dolphin has hairs lined up in a single band on both sides of the rostrum, which is their jaw, and usually has a total length of 16–17 cm .
Dolphins are a part of the species Cetacea. The epidermis of this species is characterized by the lack of keratin and by a prominent intertwine of epidermal rete pegs
Rete pegs (also known as rete processes or rete ridges) are the epithelial extensions that project into the underlying connective tissue in both skin and mucous membranes.
In the epithelium of the mouth, the attached gingiva exhibit rete pegs, whi ...
and long dermal papillae. The epidermal rete pegs are the epithelial extensions that project into the underlying connective tissue in both skin and mucous membranes. The dermal papillae are finger-like projections that help adhesion between the epidermal and dermal layers, as well as providing a larger surface area to nourish the epidermal layer. The thickness of a dolphin's epidermis varies, depending on species and age.
Blubber
Blubber is found within the dermis and subcutis layer. The dermis blends gradually with the adipose layer, which is known as fat, because the fat may extend up to the epidermis border and collagen fiber bundles extend throughout the whole subcutaneous blubber which is fat found under the skin. The thickness of the subcutaneous blubber or fat depends on the dolphin's health, development, location, reproductive state, and how well it feeds. This fat is thickest on the dolphin's back and belly. Most of the dolphin's body fat is accumulated in a thick layer of blubber. Blubber differs from fat in that, in addition to fat cells, it contains a fibrous network of connective tissue.
The blubber functions to streamline the body and to form specialized locomotor structures such as the dorsal fin, propulsive fluke blades and caudal keels. There are many nerve endings that resemble small, onion-like configurations that are present in the superficial portion of the dermis. Mechanoreceptors are found within the interlocks of the epidermis with dermal ridges. There are nerve fibers in the dermis that extend to the epidermis. These nerve endings are known to be highly proprioceptive
Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense".
Proprioception is mediated by proprioceptors, mechanosensory neurons ...
, which explains sensory perception. Proprioception, which is also known as kinesthesia, is the body's ability to sense its location, movements and actions. Dolphins are sensitive to vibrations and small pressure changes.
Blood vessels and nerve endings can be found within the dermis. There is a plexus of parallel running arteries and veins in the dorsal fin, fluke, and flippers. The blubber manipulates the blood vessels to help the dolphin stay warm. When the temperature drops, the blubber constricts the blood vessels to reduce blood flow in the dolphin. This allows the dolphin to spend less energy heating its own body, ultimately keeping the animal warmer without burning energy as quick. In order to release heat, the heat must pass the blubber layer. There are thermal windows that lack blubber, are not fully insulated and are somewhat thin and highly vascularized, including the dorsal fin, flukes, and flippers. These thermal windows are a good way for dolphins to get rid of excess heat if overheating. Additionally in order to conserve heat, dolphins use countercurrent heat exchange. Blood flows in different directions in order for heat to transfer across membranes. Heat from warm blood leaving the heart will heat up the cold blood that is headed back to the heart from the extremities, meaning that the heart always has warm blood and it decreases the heat lost to the water in those thermal windows.
Locomotion
Dolphins have two pectoral flippers, containing four digits, a boneless dorsal fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...
for stability, and a tail fin for propulsion. Although dolphins do not possess external hind limbs, some possess discrete rudimentary appendages, which may contain feet and digits. Dolphins are fast swimmers in comparison to seals which typically cruise at ; the orca, in comparison, can travel at speeds up to . The fusing of the neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, which means they are unable to turn their heads. River dolphin
River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant riv ...
s have non-fused neck vertebrae and can turn their heads up to 90°. Dolphins swim by moving their tail fin and rear body vertically, while their flippers are mainly used for steering. Some species log
Log most often refers to:
* Trunk (botany), the stem and main wooden axis of a tree, called logs when cut
** Logging, cutting down trees for logs
** Firewood, logs used for fuel
** Lumber or timber, converted from wood logs
* Logarithm, in mathe ...
out of the water, which may allow them to travel faster. Their skeletal anatomy allows them to be fast swimmers. All species have a dorsal fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...
to prevent themselves from involuntarily spinning in the water.
Some dolphins are adapted for diving to great depths. In addition to their streamlined bodies, some can selectively slow their heart rate
Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...
to conserve oxygen. Some can also re-route blood from tissue tolerant of water pressure to the heart, brain and other organs. Their hemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...
and myoglobin
Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the cardiac and skeletal muscle tissue of vertebrates in general and in almost all mammals. Myoglobin is distantly related to hemoglobin. Compared to hemoglobin, myoglobi ...
store oxygen in body tissues, and they have twice as much myoglobin as hemoglobin.
Senses
The dolphin ear has specific adaptations to the marine
Marine is an adjective meaning of or pertaining to the sea or ocean.
Marine or marines may refer to:
Ocean
* Maritime (disambiguation)
* Marine art
* Marine biology
* Marine debris
* Marine habitats
* Marine life
* Marine pollution
Military
* ...
environment. In humans, the middle ear
The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear).
The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in the ...
works as an impedance equalizer between the outside air's low impedance and the cochlea
The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory org ...
r fluid's high impedance. In dolphins, and other marine mammals, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, dolphins receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. The dolphin ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater. Dolphins send out high frequency clicks from an organ known as a melon
A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. The word "melon" can refer to either the plant or specifically to the fruit. Botanically, a melon is a kind of berry, specifically a "pepo". The ...
. This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. This allows dolphins to use echolocation for orientation. Though most dolphins do not have hair, they do have hair follicle
The hair follicle is an organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions. The hair follicle regulates hair growth via a complex interaction between h ...
s that may perform some sensory function. Beyond locating an object, echolocation also provides the animal with an idea on an object's shape and size, though how exactly this works is not yet understood. The small hairs on the rostrum of the boto
Boto is a Portuguese name given to several types of dolphins and river dolphins native to the Amazon and the Orinoco River tributaries. A few botos exist exclusively in fresh water, and these are often considered primitive dolphins.
Classificatio ...
(river dolphins of South America) are believed to function as a tactile sense
Haptic perception ( gr, haptόs, script=latn, italics=yes "palpable", ''haptikόs'' "suitable for touch") means literally the ability "to grasp something". Perception in this case is achieved through the active exploration of surfaces and objects b ...
, possibly to compensate for the boto's poor eyesight.
The dolphin eye is relatively small for its size, yet they do retain a good degree of eyesight. As well as this, the eyes of a dolphin are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. When dolphins surface, their lens and cornea correct the nearsightedness that results from the water's refraction of light. Their eyes contain both rod and cone
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex.
A cone is formed by a set of line segments, half-lines, or lines con ...
cells, meaning they can see in both dim and bright light, but they have far more rod cells than they do cone cells. They lack short wavelength sensitive visual pigments in their cone cells, indicating a more limited capacity for color vision than most mammals. Most dolphins have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a ''tapetum lucidum
The ''tapetum lucidum'' ( ; ; ) is a layer of tissue in the eye of many vertebrates and some other animals. Lying immediately behind the retina, it is a retroreflector. It reflects visible light back through the retina, increasing the light a ...
'' (eye tissue behind the retina); these adaptations allow for large amounts of light to pass through the eye and, therefore, a very clear image of the surrounding area. They also have glands on the eyelids and outer corneal layer that act as protection for the cornea.
The olfactory lobes
The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OF ...
and nerve
A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system.
A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...
are absent in dolphins, suggesting that they have no sense of smell.
Dolphins are not thought to have a good sense of taste, as their taste buds are atrophied or missing altogether. Some have preferences for different kinds of fish, indicating some ability to taste.
Intelligence
Dolphins are known to teach, learn, cooperate, scheme, and grieve. The neocortex of many species is home to elongated spindle neurons
Von Economo neurons (VENs), also called spindle neurons, are a specific class of mammalian cortical neurons characterized by a large spindle-shaped soma (or body) gradually tapering into a single apical axon (the ramification that ''transmits ...
that, prior to 2007, were known only in hominids. In humans, these cells are involved in social conduct, emotions, judgment, and theory of mind. Cetacean spindle neurons are found in areas of the brain that are homologous to where they are found in humans, suggesting that they perform a similar function.
Brain size
The size of the brain is a frequent topic of study within the fields of anatomy, biological anthropology, animal science and evolution. Brain size is sometimes measured by weight and sometimes by volume (via MRI scans or by skull volume). Neur ...
was previously considered a major indicator of the intelligence of an animal. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks. Allometric
Allometry is the study of the relationship of body size to shape, anatomy, physiology and finally behaviour, first outlined by Otto Snell in 1892, by D'Arcy Thompson in 1917 in ''On Growth and Form'' and by Julian Huxley in 1932.
Overview
Allome ...
analysis indicates that mammalian brain size scales at approximately the ⅔ or ¾ exponent of the body mass. Comparison of a particular animal's brain size with the expected brain size based on such allometric analysis provides an encephalization quotient
Encephalization quotient (EQ), encephalization level (EL), or just encephalization is a relative brain size measure that is defined as the ratio between observed to predicted brain mass for an animal of a given size, based on nonlinear regressi ...
that can be used as another indication of animal intelligence. Orca
The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only Extant taxon, extant species in the genus ''Orcinus'' and is recognizable by its black ...
s have the second largest brain mass of any animal on earth, next to the sperm whale
The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus ''Physeter'' and one of three extant species in the sperm whale famil ...
. The brain to body mass ratio
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
in some is second only to humans.
Self-awareness
In philosophy of self, self-awareness is the experience of one's own personality or individuality. It is not to be confused with consciousness in the sense of qualia. While consciousness is being aware of one's environment and body and lifesty ...
is seen, by some, to be a sign of highly developed, abstract thinking. Self-awareness, though not well-defined scientifically, is believed to be the precursor to more advanced processes like meta-cognitive reasoning (thinking about thinking) that are typical of humans. Research in this field has suggested that cetaceans, among others, possess self-awareness.
The most widely used test for self-awareness in animals is the mirror test
The mirror test—sometimes called the mark test, mirror self-recognition (MSR) test, red spot technique, or rouge test—is a behavioral technique developed in 1970 by American psychologist Gordon Gallup Jr. as an attempt to determine whether an ...
in which a mirror is introduced to an animal, and the animal is then marked with a temporary dye. If the animal then goes to the mirror in order to view the mark, it has exhibited strong evidence of self-awareness.
Some disagree with these findings, arguing that the results of these tests are open to human interpretation and susceptible to the Clever Hans
Clever Hans (German: ''der Kluge Hans''; c. 1895 - c. 1916) was a horse that was claimed to have performed arithmetic and other intellectual tasks. After a formal investigation in 1907, psychologist Oskar Pfungst demonstrated that the horse was ...
effect. This test is much less definitive than when used for primates, because primates can touch the mark or the mirror, while cetaceans cannot, making their alleged self-recognition behavior less certain. Skeptics argue that behaviors that are said to identify self-awareness resemble existing social behaviors, and so researchers could be misinterpreting self-awareness for social responses to another individual. The researchers counter-argue that the behaviors shown are evidence of self-awareness, as they are very different from normal responses to another individual. Whereas apes can merely touch the mark on themselves with their fingers, cetaceans show less definitive behavior of self-awareness; they can only twist and turn themselves to observe the mark.
In 1995, Marten and Psarakos used television to test dolphin self-awareness. They showed dolphins real-time video of themselves, video of another dolphin and recorded footage. They concluded that their evidence suggested self-awareness rather than social behavior. While this particular study has not been repeated since then, dolphins have since passed the mirror test. Some researchers have argued that evidence for self-awareness has not been convincingly demonstrated.
Behavior
![Dolphins gesture language](https://upload.wikimedia.org/wikipedia/commons/b/b0/Dolphins_gesture_language.jpg)
Socialization
Dolphins are highly social animals, often living in pods of up to a dozen individuals, though pod sizes and structures vary greatly between species and locations. In places with a high abundance of food, pods can merge temporarily, forming a ''superpod''; such groupings may exceed 1,000 dolphins. Membership in pods is not rigid; interchange is common. They establish strong social bonds, and will stay with injured or ill members, helping them to breathe by bringing them to the surface if needed. This altruism
Altruism is the principle and moral practice of concern for the welfare and/or happiness of other human beings or animals, resulting in a quality of life both material and spiritual. It is a traditional virtue in many cultures and a core as ...
does not appear to be limited to their own species. The dolphin ''Moko
In the mythology of Mangaia in the Cook Islands, Moko is a wily character and grandfather of the heroic Ngaru.
Moko is a ruler or king of the lizards, and he orders his lizard subjects to climb into the basket of the sky demon Amai-te-rangi Acco ...
'' in New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
has been observed guiding a female pygmy sperm whale
The pygmy sperm whale (''Kogia breviceps'') is one of two extant species in the family Kogiidae in the sperm whale superfamily. They are not often sighted at sea, and most of what is known about them comes from the examination of stranded spec ...
together with her calf out of shallow water where they had stranded several times. They have also been seen protecting swimmers from sharks by swimming circles around the swimmers or charging the sharks to make them go away.
Dolphins communicate using a variety of clicks, whistle-like sounds and other vocalizations. Dolphins also use nonverbal communication
Nonverbal communication (NVC) is the transmission of messages or signals through a nonverbal platform such as eye contact, facial expressions, gestures, Posture (psychology), posture, and body language. It includes the use of social cues, kinesi ...
by means of touch and posturing.
Dolphins also display culture, something long believed to be unique to humans (and possibly other primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...
species). In May 2005, a discovery in Australia found Indo-Pacific bottlenose dolphin
The Indo-Pacific bottlenose dolphin (''Tursiops aduncus'') is a species of bottlenose dolphin. This dolphin grows to long, and weighs up to . It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern co ...
s (''Tursiops aduncus'') teaching their young to use tools. They cover their snout
A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...
s with sponges
Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through ...
to protect them while foraging. This knowledge is mostly transferred by mothers to daughters, unlike simian
The simians, anthropoids, or higher primates are an infraorder (Simiiformes ) of primates containing all animals traditionally called monkeys and apes. More precisely, they consist of the parvorders New World monkeys (Platyrrhini) and Catarrhi ...
primates, where knowledge is generally passed on to both sexes. Using sponges as mouth protection is a learned behavior. Another learned behavior was discovered among river dolphins in Brazil, where some male dolphins use weeds and sticks as part of a sexual display.
Forms of care-giving between fellows and even for members of different species(see Moko (dolphin)) are recorded in various species – such as trying to save weakened fellows or female pilot whale
Pilot whales are cetaceans belonging to the genus ''Globicephala''. The two extant species are the long-finned pilot whale (''G. melas'') and the short-finned pilot whale (''G. macrorhynchus''). The two are not readily distinguishable at sea, a ...
s holding up dead calves for long periods.
Dolphins engage in acts of aggression towards each other. The older a male dolphin is, the more likely his body is to be covered with bite scars. Male dolphins can get into disputes over companions and females. Acts of aggression can become so intense that targeted dolphins sometimes go into exile after losing a fight.
Male bottlenose dolphins have been known to engage in infanticide
Infanticide (or infant homicide) is the intentional killing of infants or offspring. Infanticide was a widespread practice throughout human history that was mainly used to dispose of unwanted children, its main purpose is the prevention of reso ...
. Dolphins have also been known to kill porpoises
Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals an ...
for reasons which are not fully understood, as porpoises generally do not share the same diet as dolphins and are therefore not competitors for food supplies. The Cornwall Wildlife Trust
The Cornwall Wildlife Trust is a charitable organisation founded in 1962 that is concerned solely with Cornwall, England.
It deals with the conservation and preservation of Cornwall's wildlife, geology and habitats managing over 50 nature reser ...
records about one such death a year. Possible explanations include misdirected infanticide, misdirected sexual aggression or play behaviour.
Reproduction and sexuality
Dolphin copulation
Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetrat ...
happens belly to belly; though many species engage in lengthy foreplay
Foreplay is a set of emotionally and physically intimate acts between one or more people meant to create sexual arousal and desire for sexual activity. Although foreplay is typically understood as physical sexual activity, nonphysical activitie ...
, the actual act is usually brief, but may be repeated several times within a short timespan. The gestation period
In mammals, pregnancy is the period of reproduction during which a female carries one or more live offspring from implantation in the uterus through gestation. It begins when a fertilized zygote implants in the female's uterus, and ends once it ...
varies with species; for the small Tucuxi dolphin
The tucuxi (''Sotalia fluviatilis''), alternatively known in Peru ''bufeo gris'' or ''bufeo negro'', is a species of freshwater dolphin found in the rivers of the Amazon basin. The word ''tucuxi'' is derived from the Tupi language word ''tuchu ...
, this period is around 11 to 12 months, while for the orca, the gestation period is around 17 months. Typically dolphins give birth to a single calf, which is, unlike most other mammals, born tail first in most cases. They usually become sexually active at a young age, even before reaching sexual maturity
Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definitio ...
.[ The age of sexual maturity varies by species and gender.
Dolphins are known to display non-reproductive sexual behavior, engaging in ]masturbation
Masturbation is the sexual stimulation of one's own genitals for sexual arousal or other sexual pleasure, usually to the point of orgasm. The stimulation may involve hands, fingers, everyday objects, sex toys such as vibrators, or combinatio ...
, stimulation of the genital area of other individuals using the rostrum
Rostrum may refer to:
* Any kind of a platform for a speaker:
**dais
**pulpit
* Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects
* Rostrum (ship), a form of bow on naval ships
* Ros ...
or flippers, and homosexual contact.[
Various species of dolphin have been known to engage in sexual behavior, including copulation with dolphins of other species, and occasionally exhibit behave sexually towards other animals, including humans. . Sexual encounters may be violent, with male dolphins sometimes showing aggressive behavior towards both females and other males. Male dolphins may also work together and attempt to herd females in ]estrus
The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous p ...
, keeping the females by their side by means of both physical aggression and intimidation, to increase their chances of reproductive success.
Sleeping
Generally, dolphins sleep with only one brain hemisphere
Hemisphere refers to:
* A half of a sphere
As half of the Earth
* A hemisphere of Earth
** Northern Hemisphere
** Southern Hemisphere
** Eastern Hemisphere
** Western Hemisphere
** Land and water hemispheres
* A half of the (geocentric) celes ...
in slow-wave sleep
Slow-wave sleep (SWS), often referred to as deep sleep, consists of stage three of non-rapid eye movement sleep. It usually lasts between 70 and 90 minutes and takes place during the first hours of the night. Initially, SWS consisted of both St ...
at a time, thus maintaining enough consciousness to breathe and to watch for possible predators and other threats. Sleep stages earlier in sleep can occur simultaneously in both hemispheres.
In captivity, dolphins seemingly enter a fully asleep state where both eyes are closed and there is no response to mild external stimuli. In this case, respiration is automatic; a tail kick reflex
In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus.
Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
keeps the blowhole above the water if necessary. Anesthetized
Anesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), am ...
dolphins initially show a tail kick reflex. Though a similar state has been observed with wild sperm whale
The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus ''Physeter'' and one of three extant species in the sperm whale famil ...
s, it is not known if dolphins in the wild reach this state. The Indus river dolphin
The Indus river dolphin (''Platanista minor''), also known as the ''bhulan'' in Urdu and Sindhi, is a species of toothed whale in the family Platanistidae. It is endemic to the Indus River Basin of Pakistan and northwestern India. This dolphin ...
has a sleep method that is different from that of other dolphin species. Living in water with strong currents and potentially dangerous floating debris, it must swim continuously to avoid injury. As a result, this species sleeps in very short bursts which last between 4 and 60 seconds.
Feeding
There are various feeding methods among and within species, some apparently exclusive to a single population. Fish and squid are the main food, but the false killer whale and the orca also feed on other marine mammals. Orcas on occasion also hunt whale species larger than themselves. Different breeds of dolphins vary widely in the number of teeth they possess. The orca usually carries 40–56 teeth while the popular bottlenose dolphin has anywhere from 72 to 116 conical teeth and its smaller cousin the common dolphin has 188–268 teeth: the number of teeth that an individual carries varies widely between within a single species. Hybrids between common and bottlenose bred in captivity had a nunmber of teeth intermediate between that of their parents.
One common feeding method is herding, where a pod squeezes a school of fish into a small volume, known as a bait ball
A bait ball, or baitball, occurs when small fish swarm in a tightly packed spherical formation about a common centre. It is a last-ditch defensive measure adopted by small schooling fish when they are threatened by predators. Small schooling f ...
. Individual members then take turns plowing through the ball, feeding on the stunned fish. Corralling is a method where dolphins chase fish into shallow water to catch them more easily. Orcas and bottlenose dolphins have also been known to drive their prey onto a beach to feed on it, a behaviour known as beach or strand feeding. Some species also whack fish with their flukes, stunning them and sometimes knocking them out of the water.
Reports of cooperative human-dolphin fishing date back to the ancient Roman
In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–509 BC ...
author and natural philosopher
Natural philosophy or philosophy of nature (from Latin ''philosophia naturalis'') is the philosophical study of physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior throu ...
Pliny the Elder
Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, naturalist and natural philosopher, and naval and army commander of the early Roman Empire, and a friend of the emperor Vespasian. He wrote the encyclopedic '' ...
. A modern human-dolphin partnership currently operates in Laguna
Laguna (Italian and Spanish for lagoon) may refer to:
People
* Abe Laguna (born 1992), American DJ known as Ookay
* Andrés Laguna (1499–1559), Spanish physician, pharmacologist, and botanist
* Ana Laguna (born 1955), Spanish-Swedish ballet d ...
, Santa Catarina, Brazil. Here, dolphins drive fish towards fishermen waiting along the shore and signal the men to cast their nets. The dolphins' reward is the fish that escape the nets.
In Shark Bay
Shark Bay (Malgana: ''Gathaagudu'', "two waters") is a World Heritage Site in the Gascoyne region of Western Australia. The http://www.environment.gov.au/heritage/places/world/shark-bay area is located approximately north of Perth, on the ...
, Australia, dolphins catch fish by trapping them in huge conch shell
Conch () is a common name of a number of different medium-to-large-sized sea snail, sea snails. Conch shells typically have a high Spire (mollusc), spire and a noticeable siphonal canal (in other words, the shell comes to a noticeable point a ...
s. In "shelling", a dolphin brings the shell to the surface and shakes it, so that fish sheltering within fall into the dolphin's mouth. From 2007 to 2018, in 5,278 encounters with dolphins, researchers observed 19 dolphins shelling 42 times. The behavior spreads mainly within generations, rather than being passed from mother to offspring.
Vocalization
Dolphins are capable of making a broad range of sounds using nasal airsacs located just below the blowhole. Roughly three categories of sounds can be identified: frequency modulated
Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing.
In analog freque ...
whistles, burst-pulsed sounds, and clicks. Dolphins communicate with whistle-like sounds produced by vibrating connective tissue, similar to the way human vocal cords function, and through burst-pulsed sounds, though the nature and extent of that ability is not known. The clicks are directional and are for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interest. Dolphin echolocation clicks are amongst the loudest sounds made by marine animals.
Bottlenose dolphins have been found to have signature whistles, a whistle that is unique to a specific individual. These whistles are used in order for dolphins to communicate with one another by identifying an individual. It can be seen as the dolphin equivalent of a name for humans. These signature whistles are developed during a dolphin's first year; it continues to maintain the same sound throughout its lifetime. In order to obtain each individual whistle sound, dolphins undergo vocal production learning. This consists of an experience with other dolphins that modifies the signal structure of an existing whistle sound. An auditory experience influences the whistle development of each dolphin. Dolphins are able to communicate to one another by addressing another dolphin through mimicking their whistle. The signature whistle of a male bottlenose dolphin tends to be similar to that of his mother, while the signature whistle of a female bottlenose dolphin tends to be more distinguishing. Bottlenose dolphins have a strong memory when it comes to these signature whistles, as they are able to relate to a signature whistle of an individual they have not encountered for over twenty years. Research done on signature whistle usage by other dolphin species is relatively limited. The research on other species done so far has yielded varied outcomes and inconclusive results.
Because dolphins are generally associated in groups, communication is necessary. Signal masking is when other similar sounds (conspecific sounds) interfere with the original acoustic sound. In larger groups, individual whistle sounds are less prominent. Dolphins tend to travel in pods, upon which there are groups of dolphins that range from a few to many. Although they are traveling in these pods, the dolphins do not necessarily swim right next to each other. Rather, they swim within the same general vicinity. In order to prevent losing one of their pod members, there are higher whistle rates. Because their group members were spread out, this was done in order to continue traveling together.
Jumping and playing
Dolphins frequently leap above the water surface, this being done for various reasons. When travelling, jumping can save the dolphin energy as there is less friction while in the air. This type of travel is known as porpoising. Other reasons include orientation, social displays, fighting, non-verbal communication
Nonverbal communication (NVC) is the transmission of messages or signals through a nonverbal platform such as eye contact, facial expressions, gestures, posture, and body language. It includes the use of social cues, kinesics, distance (proxemic ...
, entertainment and attempting to dislodge parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
s.
Dolphins show various types of playful behavior, often including objects, self-made bubble ring
A bubble ring, or toroidal bubble, is an underwater vortex ring where an air bubble occupies the core of the vortex, forming a ring shape. The ring of air as well as the nearby water spins poloidally as it travels through the water, much like a ...
s, other dolphins or other animals.[Robin D. Paulos (2010), ''Play in Wild and Captive Cetaceans''] When playing with objects or small animals, common behavior includes carrying the object or animal along using various parts of the body, passing it along to other members of the group or taking it from another member, or throwing it out of the water. Dolphins have also been observed harassing animals in other ways, for example by dragging birds underwater without showing any intent to eat them. Playful behaviour that involves another animal species with active participation of the other animal has also been observed. Playful dolphin interactions with humans are the most obvious examples, followed by those with humpback whale
The humpback whale (''Megaptera novaeangliae'') is a species of baleen whale. It is a rorqual (a member of the family Balaenopteridae) and is the only species in the genus ''Megaptera''. Adults range in length from and weigh up to . The hump ...
s and dog
The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...
s.
Juvenile dolphins off the coast of Western Australi have been observed chasing, capturing, and chewing on blowfish
Tetraodontidae is a family of primarily marine and estuarine fish of the order Tetraodontiformes. The family includes many familiar species variously called pufferfish, puffers, balloonfish, blowfish, blowies, bubblefish, globefish, swellfis ...
. While some reports state that the dolphins are becoming intoxicated on the tetrodotoxin
Tetrodotoxin (TTX) is a potent neurotoxin. Its name derives from Tetraodontiformes, an order that includes pufferfish, porcupinefish, ocean sunfish, and triggerfish; several of these species carry the toxin. Although tetrodotoxin was discovered ...
in the fishes' skin, other reports have characterized this behavior as the normal curiosity and exploration of their environment in which dolphins engage.
Tail-walking
Although this behaviour is highly unusual in wild dolphins, several Indo-Pacific bottlenose dolphin
The Indo-Pacific bottlenose dolphin (''Tursiops aduncus'') is a species of bottlenose dolphin. This dolphin grows to long, and weighs up to . It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern co ...
s (''Tursiops aduncus'') of the Port River
The Port River (officially known as the Port Adelaide River) is part of a tidal estuary located north of the Adelaide city centre in the Australian state of South Australia. It has been used as a shipping channel since the beginning of European ...
, north of Adelaide
Adelaide ( ) is the capital city of South Australia, the state's largest city and the fifth-most populous city in Australia. "Adelaide" may refer to either Greater Adelaide (including the Adelaide Hills) or the Adelaide city centre. The dem ...
, South Australia
South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...
, have been seen to have exhibit "tail-walking". This activity mimicks a standing posture, using the tail to run backwards along the water. To perform this movement, the dolphin "forces the majority of its body vertically out of the water and maintains the position by vigorously pumping its tail".[
This started in 1988 when a female named Billie was rescued after becoming trapped in a polluted ]marina
A marina (from Spanish , Portuguese and Italian : ''marina'', "coast" or "shore") is a dock or basin with moorings and supplies for yachts and small boats.
A marina differs from a port in that a marina does not handle large passenger ships o ...
, and spent two weeks recuperating with captive dolphins. Billie had previously been observed swimming and frolicking with racehorse
Horse racing is an equestrian performance sport, typically involving two or more horses ridden by jockeys (or sometimes driven without riders) over a set distance for competition. It is one of the most ancient of all sports, as its basic pr ...
s exercising in the Port River in the 1980s. After becoming trapped in a reedy estuary further down the coast, she was rescued and placed with several captive dolphins at a marine park to recuperate. There she observed the captive dolphins performing tail-walking.[ After being returned to the Port River, she continued to perform this trick, and another dolphin, Wave, copied her. Wave, a very active tail-walker, passed on the skill to her daughters, Ripple and Tallula.]
After Billie's premature death, Wave started tail-walking much more frequently, and other dolphins in the group were observed also performing the behaviour.[ In 2011, up to 12 dolphins were observed tail-walking, but only females appeared to learn the skill.] In October 2021, a dolphin was observed tail-walking over a number of hours.
Scientists have found the spread of this behaviour, through up to two generations, surprising, as it brings no apparent advantage, and is very energy-consuming.[ A 2018 study by Mike Rossley et al. suggested:][
]
Threats
Dolphins have few marine enemies. Some species or specific populations have none, making them apex predator
An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own.
Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic lev ...
s. For most of the smaller species of dolphins, only a few of the larger sharks, such as the bull shark
The bull shark (''Carcharhinus leucas''), also known as the Zambezi shark (informally zambi) in Africa and Lake Nicaragua shark in Nicaragua, is a species of requiem shark commonly found worldwide in warm, shallow waters along coasts and in riv ...
, dusky shark, tiger shark
The tiger shark (''Galeocerdo cuvier'') is a species of requiem shark and the last extant member of the family Galeocerdonidae. It is a large macropredator, capable of attaining a length over . Populations are found in many tropical and tempera ...
and great white shark
The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large mackerel shark which can be found in the coastal surface waters of all the major oceans. It is nota ...
, are a potential risk, especially for calves. Some of the larger dolphin species, especially orcas
The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus ''Orcinus'' and is recognizable by its black-and-white pat ...
, may also prey on smaller dolphins, but this seems rare. Dolphins also suffer from a wide variety of diseases and parasites. The Cetacean morbillivirus
''Cetacean morbillivirus'' (CeMV) is a virus that infects marine mammals in the order Cetacea, which includes dolphins, porpoises and whales. Three genetically distinct strains have been identified: dolphin morbillivirus (DMV), pilot whale mor ...
in particular has been known to cause regional epizootics
In epizoology, an epizootic (from Greek: ''epi-'' upon + ''zoon'' animal) is a disease event in a nonhuman animal population analogous to an epidemic in humans. An epizootic may be restricted to a specific locale (an "outbreak"), general (an "epi ...
often leaving hundreds of animals of various species dead. Symptoms of infection are often a severe combination of pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...
, encephalitis
Encephalitis is inflammation of the brain. The severity can be variable with symptoms including reduction or alteration in consciousness, headache, fever, confusion, a stiff neck, and vomiting. Complications may include seizures, hallucinations, ...
and damage to the immune system, which greatly impair the cetacean's ability to swim and stay afloat unassisted. A study at the U.S. National Marine Mammal Foundation revealed that dolphins, like humans, develop a natural form of type 2 diabetes
Type 2 diabetes, formerly known as adult-onset diabetes, is a form of diabetes mellitus that is characterized by high blood sugar, insulin resistance, and relative lack of insulin. Common symptoms include increased thirst, frequent urination, ...
which may lead to a better understanding of the disease and new treatments for both humans and dolphins.
Dolphins can tolerate and recover from extreme injuries such as shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...
bites although the exact methods used to achieve this are not known. The healing
With physical trauma or disease suffered by an organism, healing involves the repairing of damaged tissue(s), organs and the biological system as a whole and resumption of (normal) functioning. Medicine includes the process by which the cells i ...
process is rapid and even very deep wounds do not cause dolphins to hemorrhage
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...
to death. Furthermore, even gaping wounds restore in such a way that the animal's body shape is restored, and infection of such large wounds seems rare.
A study published in the journal ''Marine Mammal Science'' suggests that at least some dolphins survive shark attacks using everything from sophisticated combat moves to teaming up against the shark.
Humans
Some dolphin species are at risk of extinction, especially some river dolphin species such as the Amazon river dolphin, and the Ganges
The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma ( )). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international river to which India, Bangladesh, Nepal and China are the riparian states." is ...
and Yangtze river dolphin
The baiji (; IPA: ; ''Lipotes vexillifer'', ''Lipotes'' meaning "left behind" and ''vexillifer'' "flag bearer") is a possibly extinct species of freshwater dolphin native to the Yangtze river system in China. It is thought to be the first dolph ...
, which are critically or seriously endangered. A 2006 survey found no individuals of the Yangtze river dolphin. The species now appears to be functionally extinct
Functional extinction is the extinction of a species or other taxon such that:
#It disappears from the fossil record, or historic reports of its existence cease;
#The reduced population no longer plays a significant role in ecosystem function; or ...
.
Pesticides
Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampric ...
, heavy metals, plastics, and other industrial and agricultural pollutants that do not disintegrate rapidly in the environment concentrate in predators such as dolphins. Injuries or deaths due to collisions with boats, especially their propeller
A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
s, are also common.
Various fishing methods, most notably purse seine fishing
Seine fishing (or seine-haul fishing; ) is a method of fishing that employs a surrounding net, called a seine, that hangs vertically in the water with its bottom edge held down by weights and its top edge buoyed by floats. Seine nets can be dep ...
for tuna
A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max length: ...
and the use of drift
Drift or Drifts may refer to:
Geography
* Drift or ford (crossing) of a river
* Drift, Kentucky, unincorporated community in the United States
* In Cornwall, England:
** Drift, Cornwall, village
** Drift Reservoir, associated with the village
...
and gill net
Gillnetting is a fishing method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is ...
s, unintentionally kill many dolphins. Accidental by-catch
Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...
in gill nets and incidental captures in antipredator nets that protect marine fish farms are common and pose a risk for mainly local dolphin populations. In some parts of the world, such as Taiji
Tai chi (), short for Tai chi ch'üan ( zh, s=太极拳, t=太極拳, first=t, p=Tàijíquán, labels=no), sometimes called " shadowboxing", is an internal Chinese martial art practiced for defense training, health benefits and meditation. T ...
in Japan and the Faroe Islands
The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic island group and an autonomous territory of the Kingdom of Denmark.
They are located north-northwest of Scotland, and about halfway bet ...
, dolphins are traditionally considered food and are killed in harpoon
A harpoon is a long spear-like instrument and tool used in fishing, whaling, seal hunting, sealing, and other marine hunting to catch and injure large fish or marine mammals such as seals and whales. It accomplishes this task by impaling the t ...
or drive hunts.[
] Dolphin meat is high in mercury and may thus pose a health danger to humans when consumed.
Queensland's shark culling
Shark culling is the deliberate killing of sharks by government authorities, usually in response to one or more shark attacks. The term "shark control" is often used by governments when referring to culls. Shark culling has been criticized by envi ...
program, which has killed roughly 50,000 sharks since 1962, has also killed thousands of dolphins as bycatch. "Shark control" programs in both Queensland and New South Wales
)
, nickname =
, image_map = New South Wales in Australia.svg
, map_caption = Location of New South Wales in AustraliaCoordinates:
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, es ...
use shark nets
A shark net is a submerged section of gillnets placed at beaches designed to intercept large marine animals including sharks, with the aim to reduce the likelihood of shark attacks on swimmers. Shark nets used are gillnets which is a wall of net ...
and drum lines
A drum line is an unmanned aquatic trap used to lure and capture large sharks using baited hooks. They are typically deployed near popular swimming beaches with the intention of reducing the number of sharks in the vicinity and therefore the prob ...
, which entangle and kill dolphins. Queensland's "shark control" program has killed more than 1,000 dolphins in recent years, and at least 32 dolphins have been killed in Queensland since 2014. A shark culling
Shark culling is the deliberate killing of sharks by government authorities, usually in response to one or more shark attacks. The term "shark control" is often used by governments when referring to culls. Shark culling has been criticized by envi ...
program in KwaZulu-Natal
KwaZulu-Natal (, also referred to as KZN and known as "the garden province") is a province of South Africa that was created in 1994 when the Zulu bantustan of KwaZulu ("Place of the Zulu" in Zulu) and Natal Province were merged. It is locate ...
has killed at least 2,310 dolphins.
Dolphin safe label
Dolphin-safe labels are used to denote compliance with laws or policies designed to minimize dolphin fatalities during fishing for tuna destined for canning.
Some labels impose stricter requirements than others. Dolphin-safe tuna labeling originat ...
s attempt to reassure consumers that fish and other marine products have been caught in a dolphin-friendly way. The earliest campaigns with "dolphin safe" labels were initiated in the 1980s as a result of cooperation between marine activists and the major tuna companies, and involved decreasing incidental dolphin kills by up to 50% by changing the type of nets used to catch tuna. The dolphins are netted only while fishermen are in pursuit of smaller tuna. Albacore are not netted this way, making albacore the only truly dolphin-safe tuna.
Loud underwater noises, such as those resulting from naval
A navy, naval force, or maritime force is the branch of a nation's armed forces principally designated for naval warfare, naval and amphibious warfare; namely, lake-borne, riverine, littoral zone, littoral, or ocean-borne combat operations and ...
sonar
Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigation, navigate, measure distances (ranging), communicate with or detect o ...
use, live firing exercises, and certain offshore construction
Offshore construction is the installation of structures and facilities in a marine environment, usually for the production and transmission of electricity, oil, gas and other resources. It is also called maritime engineering.
Construction a ...
projects such as wind farm
A wind farm or wind park, also called a wind power station or wind power plant, is a group of wind turbines in the same location used Wind power, to produce electricity. Wind farms vary in size from a small number of turbines to several hundre ...
s, may be harmful to dolphins, increasing stress, damaging hearing, and causing decompression sickness
Decompression sickness (abbreviated DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompressio ...
by forcing them to surface too quickly to escape the noise.
Dolphins and other smaller cetaceans are also hunted in an activity known as dolphin drive hunting. This is accomplished by driving a pod together with boats and usually into a bay or onto a beach. Their escape is prevented by closing off the route to the ocean with other boats or nets. Dolphins are hunted this way in several places around the world, including the Solomon Islands
Solomon Islands is an island country consisting of six major islands and over 900 smaller islands in Oceania, to the east of Papua New Guinea and north-west of Vanuatu. It has a land area of , and a population of approx. 700,000. Its capita ...
, the Faroe Islands
The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic island group and an autonomous territory of the Kingdom of Denmark.
They are located north-northwest of Scotland, and about halfway bet ...
, Peru
, image_flag = Flag of Peru.svg
, image_coat = Escudo nacional del Perú.svg
, other_symbol = Great Seal of the State
, other_symbol_type = Seal (emblem), National seal
, national_motto = "Fi ...
, and Japan, the most well-known practitioner of this method. By numbers, dolphins are mostly hunted for their meat
Meat is animal flesh that is eaten as food. Humans have hunted, farmed, and scavenged animals for meat since prehistoric times. The establishment of settlements in the Neolithic Revolution allowed the domestication of animals such as chic ...
, though some end up in dolphinarium
A dolphinarium is an aquarium for dolphins. The dolphins are usually kept in a pool, though occasionally they may be kept in pens in the open sea, either for research or public performances. Some dolphinariums consist of one pool where dolphins pe ...
s. Despite the controversial nature of the hunt resulting in international criticism, and the possible health risk that the often polluted meat causes, thousands of dolphins are caught in drive hunts each year.
Impacts of climate change
Dolphins are marine mammals with broad geographic extent, making them susceptible to climate change in various ways. The most common effect of climate change on dolphins is the increasing water temperatures across the globe. This has caused a large variety of dolphin species to experience range shifts, in which the species move from their typical geographic region to cooler waters. Another side effect of increasing water temperatures is the increase in harmful algae blooms, which has caused a mass die-off of bottlenose dolphins.
In California
California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
, the 1982-83 El Niño
El Niño (; ; ) is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date L ...
warming event caused the near-bottom spawning market squid to leave southern California, which caused their predator, the pilot whale
Pilot whales are cetaceans belonging to the genus ''Globicephala''. The two extant species are the long-finned pilot whale (''G. melas'') and the short-finned pilot whale (''G. macrorhynchus''). The two are not readily distinguishable at sea, a ...
, to also leave. As the market squid returned six years later, Risso's dolphins came to feed on the squid. Bottlenose dolphins
Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the common ...
expanded their range from southern to central California, and stayed even after the warming event subsided. The Pacific white-sided dolphin
The Pacific white-sided dolphin (''Lagenorhynchus obliquidens''), also known as the hookfin porpoise, is an active dolphin found in the cool or temperate waters of the North Pacific Ocean.
Taxonomy
The Pacific white-sided dolphin was named by Sm ...
has had a decline in population in the southwest Gulf of California
The Gulf of California ( es, Golfo de California), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Bermejo''), is a marginal sea of the Pacific Ocean that separates the Baja Ca ...
, the southern boundary of their distribution. In the 1980s they were abundant with group sizes up to 200 across the entire cool season. Then, in the 2000s, only two groups were recorded with sizes of 20 and 30, and only across the central cool season. This decline was not related to a decline of other marine mammals or prey, so it was concluded to have been caused by climate change as it occurred during a period of warming. Additionally, the Pacific white-sided dolphin had an increase in occurrence on the west coast of Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
from 1984 to 1998.
In the Mediterranean
The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...
, sea surface temperatures
Sea surface temperature (SST), or ocean surface temperature, is the ocean temperature close to the surface. The exact meaning of ''surface'' varies according to the measurement method used, but it is between and below the sea surface. Air masse ...
have increased, as well as salinity
Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...
, upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutr ...
intensity, and sea levels. Because of this, prey resources have been reduced causing a steep decline in the short-beaked common dolphin
The common dolphin (''Delphinus delphis'') is the most abundant cetacean in the world, with a global population of about six million. Despite this fact and its vernacular name, the common dolphin is not thought of as the archetypal dolphin, with ...
Mediterranean subpopulation, which was deemed endangered in 2003. This species now only exists in the Alboran Sea
The Alboran Sea (from Arabic , ''al-Baḥrān'') is the westernmost portion of the Mediterranean Sea, lying between the Iberian Peninsula and the north of Africa (Spain on the north and Morocco and Algeria on the south). The Strait of Gibraltar, w ...
, due to its high productivity, distinct ecosystem, and differing conditions from the rest of the Mediterranean.
In northwest Europe, many dolphin species have experienced range shifts from the region's typically colder waters. Warm water dolphins, like the short-beaked common dolphin and striped dolphin
The striped dolphin (''Stenella coeruleoalba'') is an extensively studied dolphin found in temperate and tropical waters of all the world's oceans. It is a member of the oceanic dolphin family, Delphinidae.
Taxonomy
The striped dolphin is one o ...
, have expanded north of western Britain and into the northern North Sea
The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...
, even in the winter, which may displace the white-beaked and Atlantic white-sided dolphin
The Atlantic white-sided dolphin (''Lagenorhynchus acutus'') is a distinctively coloured dolphin found in the cool to temperate waters of the North Atlantic Ocean.
Description
The dolphin is slightly larger than most other oceanic dolphins. It ...
that are in that region. The white-beaked dolphin has shown an increase in the southern North Sea since the 1960s because of this. The rough-toothed dolphin
The rough-toothed dolphin (''Steno bredanensis'') is a species of dolphin that can be found in deep warm and tropical waters around the world.
The species was first described by Georges Cuvier in 1823. The genus name ''Steno'', of which this spe ...
and Atlantic spotted dolphin
The Atlantic spotted dolphin (''Stenella frontalis'') is a dolphin found in warm temperate and tropical waters of the Atlantic Ocean. Older members of the species have a very distinctive spotted coloration all over their bodies.
Taxonomy
The Atl ...
may move to northwest Europe. In northwest Scotland
Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
, white-beaked dolphins (local to the colder waters of the North Atlantic) have decreased while common dolphins (local to warmer waters) have increased from 1992 to 2003. Additionally, Fraser's dolphin
Fraser's dolphin or the Sarawak dolphin (''Lagenodelphis hosei'') is a cetacean in the family Delphinidae found in deep waters in the Pacific Ocean and to a lesser extent in the Indian and Atlantic Oceans.
Taxonomy
''Lagenodelphis hosei'' is spe ...
, found in tropical waters, was recorded in the UK for the first time in 1996.
River dolphins
River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant riv ...
are highly affected by climate change as high evaporation rates, increased water temperatures, decreased precipitation, and increased acidification
Acidification may refer to:
* Ocean acidification, decrease in the pH of the Earth's oceans
* Freshwater acidification, atmospheric depositions and soil leaching of SOx and NOx
* Soil acidification, buildup of hydrogen cations, which reduces the ...
occur. River dolphins typically have a higher densities when rivers have a lox index of freshwater degradation and better water quality. Specifically looking at the Ganges river dolphin
The Ganges river dolphin (''Platanista gangetica'') is a species of toothed whale classified in the family Platanistidae. It lives in the Ganges and related rivers of South Asia, namely in the countries of India, Nepal, and Bangladesh. It is rel ...
, the high evaporation rates and increased flooding on the plains may lead to more human river regulation, decreasing the dolphin population.
As warmer waters lead to a decrease in dolphin prey, this led to other causes of dolphin population decrease. In the case of bottlenose dolphins, mullet populations decrease due to increasing water temperatures, which leads to a decrease in the dolphins' health and thus their population. At the Shark Bay World Heritage Area in Western Australia, the local Indo-Pacific bottlenose dolphin
The Indo-Pacific bottlenose dolphin (''Tursiops aduncus'') is a species of bottlenose dolphin. This dolphin grows to long, and weighs up to . It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern co ...
population had a significant decline after a marine heatwave in 2011. This heatwave caused a decrease in prey, which led to a decline in dolphin reproductive rates as female dolphins could not get enough nutrients to sustain a calf. The resultant decrease in fish population due to warming waters has also influenced humans to see dolphins as fishing competitors or even bait. Humans use dusky dolphins as bait or are killed off because they consume the same fish humans eat and sell for profit. In the central Brazilian Amazon alone, approximately 600 pink river dolphins are killed each year to be used as bait.
Relationships with humans
In history and religion
Dolphins have long played a role in human culture.
In Greek myths
A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities of de ...
, dolphins were seen invariably as helpers of humankind. Dolphins also seem to have been important to the Minoans, judging by artistic evidence from the ruined palace at Knossos
Knossos (also Cnossos, both pronounced ; grc, Κνωσός, Knōsós, ; Linear B: ''Ko-no-so'') is the largest Bronze Age archaeological site on Crete and has been called Europe's oldest city.
Settled as early as the Neolithic period, the na ...
. During the 2009 excavations of a major Mycenaean city at Iklaina
Iklaina ( el, Ίκλαινα) is a historic village in the municipal unit of Pylos, Messenia, Greece. The settlement, which is situated in low hills approximately northeast of Pylos, stands upon the remains of a Late Bronze Age (ca. 1600-1100 BC) ...
, a striking fragment of a wall-paintings came to light, depicting a ship with three human figures and dolphins. Dolphins are common in Greek mythology
A major branch of classical mythology, Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the Cosmogony, origin and Cosmology#Metaphysical co ...
, and many coins from ancient Greece
Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...
have been found which feature a man, a boy or a deity riding on the back of a dolphin. The Ancient Greeks
Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cultu ...
welcomed dolphins; spotting dolphins riding in a ship's wake was considered a good omen. In both ancient and later art, Cupid
In classical mythology, Cupid (Latin Cupīdō , meaning "passionate desire") is the god of desire, lust, erotic love, attraction and affection. He is often portrayed as the son of the love goddess Venus (mythology), Venus and the god of war Mar ...
is often shown riding a dolphin. A dolphin rescued the poet Arion
Arion (; grc-gre, Ἀρίων; fl. c. 700 BC) was a kitharode in ancient Greece, a Dionysiac poet credited with inventing the dithyramb. The islanders of Lesbos claimed him as their native son, but Arion found a patron in Periander, tyrant ...
from drowning and carried him safe to land, at Cape Matapan
Cape Matapan ( el, Κάβο Ματαπάς, Maniot dialect: Ματαπά), also named as Cape Tainaron or Taenarum ( el, Ακρωτήριον Ταίναρον), or Cape Tenaro, is situated at the end of the Mani Peninsula, Greece. Cape Matapa ...
, a promontory forming the southernmost point of the Peloponnesus
The Peloponnese (), Peloponnesus (; el, Πελοπόννησος, Pelopónnēsos,(), or Morea is a peninsula and geographic region in southern Greece. It is connected to the central part of the country by the Isthmus of Corinth land bridge which ...
. There was a temple to Poseidon
Poseidon (; grc-gre, Ποσειδῶν) was one of the Twelve Olympians in ancient Greek religion and myth, god of the sea, storms, earthquakes and horses.Burkert 1985pp. 136–139 In pre-Olympian Bronze Age Greece, he was venerated as a ch ...
and a statue of Arion riding the dolphin.
The Greeks reimagined the Phoenicia
Phoenicia () was an ancient thalassocratic civilization originating in the Levant region of the eastern Mediterranean, primarily located in modern Lebanon. The territory of the Phoenician city-states extended and shrank throughout their histor ...
n god Melqart
Melqart (also Melkarth or Melicarthus) was the tutelary god of the Phoenician city-state of Tyre and a major deity in the Phoenician and Punic pantheons. Often titled the "Lord of Tyre" (''Ba‘al Ṣūr''), he was also known as the Son of ...
as Melikertês (Melicertes
In Greek mythology, Melicertes ( grc, Μελικέρτης, Melikértēs, sometimes Melecertes), later called Palaemon or Palaimon (), was a Boeotian prince as the son of King Athamas and Ino, daughter of King Cadmus of Thebes. He was the brot ...
) and made him the son of Athamas
In Greek mythology, Athamas (; grc, Ἀθάμας, Athámas) was a Boeotian king.Apollodorus1.9.1/ref>
Family
Athamas was formerly a Thessalian prince and the son of King Aeolus of Aeolia and Enarete, daughter of Deimachus. He was the brothe ...
and Ino. He drowned but was transfigured as the marine deity Palaemon, while his mother became Leucothea
In Greek mythology, Leucothea (; grc-gre, Λευκοθέα, Leukothéa, white goddess), sometimes also called Leucothoe ( grc-gre, Λευκοθόη, Leukothóē), was one of the aspects under which an ancient sea goddess was recognized, in this ...
. (''cf'' Ino.) At Corinth, he was so closely connected with the cult of Poseidon that the Isthmian Games
Isthmian Games or Isthmia (Ancient Greek: Ἴσθμια) were one of the Panhellenic Games of Ancient Greece, and were named after the Isthmus of Corinth, where they were held. As with the Nemean Games, the Isthmian Games were held both the year ...
, originally instituted in Poseidon's honor, came to be looked upon as the funeral games of Melicertes
In Greek mythology, Melicertes ( grc, Μελικέρτης, Melikértēs, sometimes Melecertes), later called Palaemon or Palaimon (), was a Boeotian prince as the son of King Athamas and Ino, daughter of King Cadmus of Thebes. He was the brot ...
. Phalanthus In Greek mythology, Phalanthus (; Ancient Greek: Φάλανθος) is the name of three men.
* Phalanthus of Tanagra, one of the defenders of Thebes in the war of the Seven against Thebes. He was killed by Hippomedon.
* Phalanthus of Tarentum, the ...
was another legendary character brought safely to shore (in Italy) on the back of a dolphin, according to Pausanias Pausanias ( el, Παυσανίας) may refer to:
*Pausanias of Athens, lover of the poet Agathon and a character in Plato's ''Symposium''
*Pausanias the Regent, Spartan general and regent of the 5th century BC
*Pausanias of Sicily, physician of th ...
.
Dionysus
In ancient Greek religion and myth, Dionysus (; grc, Διόνυσος ) is the god of the grape-harvest, winemaking, orchards and fruit, vegetation, fertility, insanity, ritual madness, religious ecstasy, festivity, and theatre. The Romans ...
was once captured by Etruscan __NOTOC__
Etruscan may refer to:
Ancient civilization
*The Etruscan language, an extinct language in ancient Italy
*Something derived from or related to the Etruscan civilization
**Etruscan architecture
**Etruscan art
**Etruscan cities
** Etrusca ...
pirate
Piracy is an act of robbery or criminal violence by ship or boat-borne attackers upon another ship or a coastal area, typically with the goal of stealing cargo and other valuable goods. Those who conduct acts of piracy are called pirates, v ...
s who mistook him for a wealthy prince they could ransom. After the ship set sail Dionysus invoked his divine powers, causing vines to overgrow the ship where the mast and sails had been. He turned the oars into serpents, so terrifying the sailors that they jumped overboard, but Dionysus took pity on them and transformed them into dolphins so that they would spend their lives providing help for those in need. Dolphins were also the messengers of Poseidon and sometimes did errands for him as well. Dolphins were sacred to both Aphrodite
Aphrodite ( ; grc-gre, Ἀφροδίτη, Aphrodítē; , , ) is an ancient Greek goddess associated with love, lust, beauty, pleasure, passion, and procreation. She was syncretized with the Roman goddess . Aphrodite's major symbols include ...
and Apollo
Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label=Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label= ...
.
"Dolfin" was the name of an aristocratic family in the maritime Republic of Venice
The Republic of Venice ( vec, Repùblega de Venèsia) or Venetian Republic ( vec, Repùblega Vèneta, links=no), traditionally known as La Serenissima ( en, Most Serene Republic of Venice, italics=yes; vec, Serenìsima Repùblega de Venèsia, ...
, whose most prominent member was the 13th-century Doge
A doge ( , ; plural dogi or doges) was an elected lord and head of state in several Italian city-states, notably Venice and Genoa, during the medieval and renaissance periods. Such states are referred to as " crowned republics".
Etymology
The ...
Giovanni Dolfin
Giovanni Dolfin, also known as Giovanni Delfino or Delfin (died 12 July 1361) was the fifty-seventh Doge of Venice, appointed on August 13, 1356. Despite his value as general, during his reign Republic of Venice, Venice lost Dalmatia. He was blin ...
.
In Hindu mythology
Hindu mythology is the body of myths and literature attributed to, and espoused by, the adherents of the Hindu religion, found in Hindu texts such as the Vedic literature, epics like ''Mahabharata'' and ''Ramayana'', the Puranas, and reg ...
the Ganges river dolphin
The Ganges river dolphin (''Platanista gangetica'') is a species of toothed whale classified in the family Platanistidae. It lives in the Ganges and related rivers of South Asia, namely in the countries of India, Nepal, and Bangladesh. It is rel ...
is associated with Ganga
The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma ( )). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international river to which India, Bangladesh, Nepal and China are the riparian states." is ...
, the deity of the Ganges
The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma ( )). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international river to which India, Bangladesh, Nepal and China are the riparian states." is ...
river. The dolphin is said to be among the creatures which heralded the goddess' descent from the heavens and her mount, the Makara
''Makara'' ( sa, मकर, translit=Makara) is a legendary sea-creature in Hindu mythology. In Hindu astrology, Makara is equivalent to the Zodiac sign Capricorn.
Makara appears as the vahana (vehicle) of the river goddess Ganga, Narmada, a ...
, is sometimes depicted as a dolphin.
The Boto
Boto is a Portuguese name given to several types of dolphins and river dolphins native to the Amazon and the Orinoco River tributaries. A few botos exist exclusively in fresh water, and these are often considered primitive dolphins.
Classificatio ...
, a species of river dolphin
River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant riv ...
that resides in the Amazon River
The Amazon River (, ; es, Río Amazonas, pt, Rio Amazonas) in South America is the largest river by discharge volume of water in the world, and the disputed longest river system in the world in comparison to the Nile.
The headwaters of t ...
, are believed to be shapeshifters, or '' encantados'', who are capable of having children with human women.
There are comparatively few surviving myths of dolphins in Polynesia
Polynesia () "many" and νῆσος () "island"), to, Polinisia; mi, Porinihia; haw, Polenekia; fj, Polinisia; sm, Polenisia; rar, Porinetia; ty, Pōrīnetia; tvl, Polenisia; tkl, Polenihia (, ) is a subregion of Oceania, made up of ...
n cultures, in spite of their maritime traditions and relevance of other marine animals such as sharks
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorp ...
and seabirds
Seabirds (also known as marine birds) are birds that are adaptation, adapted to life within the marine (ocean), marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent ev ...
; unlike these, they are more often perceived as food than as totemic symbols. Dolphins are most clearly represented in Rapa Nui
Easter Island ( rap, Rapa Nui; es, Isla de Pascua) is an island and special territory of Chile in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian Triangle in Oceania. The island is most famous for its nearly ...
Rongorongo
Rongorongo (Rapa Nui: ) is a system of glyphs discovered in the 19th century on Rapa Nui (Easter Island) that appears to be writing or proto-writing. Numerous attempts at decipherment have been made, with none being successful. Although some c ...
, and in the traditions of the Caroline Islands
The Caroline Islands (or the Carolines) are a widely scattered archipelago of tiny islands in the western Pacific Ocean, to the north of New Guinea. Politically, they are divided between the Federated States of Micronesia (FSM) in the centra ...
they are depicted similarly to the Boto, being sexually active shapeshifters.
Heraldry
Dolphins are also used as symbols, for instance in heraldry. When heraldry developed in the Middle Ages
In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...
, little was known about the biology of the dolphin and it was often depicted as a sort of fish. The stylised heraldic dolphin still conventionally follows this tradition, sometimes showing the dolphin skin covered with fish scale
A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as we ...
s.
A well-known historical example was the coat of arms of the former province of the Dauphiné
The Dauphiné (, ) is a former province in Southeastern France, whose area roughly corresponded to that of the present departments of Isère, Drôme and Hautes-Alpes. The Dauphiné was originally the Dauphiné of Viennois.
In the 12th centu ...
in southern France, from which were derived the arms and the title of the Dauphin of France
Dauphin of France (, also ; french: Dauphin de France ), originally Dauphin of Viennois (''Dauphin de Viennois''), was the title given to the heir apparent to the throne of France from 1350 to 1791, and from 1824 to 1830. The word ''dauphin'' ...
, the heir to the former throne of France (the title literally meaning "The Dolphin of France").
Dolphins are present in the coat of arms of Anguilla
A coat typically is an outer garment for the upper body as worn by either gender for warmth or fashion. Coats typically have long sleeves and are open down the front and closing by means of buttons, zippers, hook-and-loop fasteners, toggles, a ...
and the coat of arms of Romania
The coat of arms of Romania was adopted in the Parliament of Romania, Romanian Parliament on 10 September 1992 as a representative coat of arms for Romania. It is based on the Lesser Coat of Arms of the Kingdom of Romania (used between 1922 and ...
, and the coat of arms of Barbados
The coat of arms of Barbados was adopted on 14 February 1966, by a royal warrant (document), royal warrant of Queen Elizabeth II. The coat of arms of Barbados was presented by the Queen to the then List of presidents of the Senate of Barbados, ...
has a dolphin supporter
In heraldry, supporters, sometimes referred to as ''attendants'', are figures or objects usually placed on either side of the shield and depicted holding it up.
Early forms of supporters are found in medieval seals. However, unlike the coro ...
.
The coat of arms of the town of Poole, Dorset, England, first recorded in 1563, includes a dolphin, which was historically depicted in stylised heraldic form, but which since 1976 has been depicted naturalistically.
In captivity
Species
The renewed popularity of dolphins in the 1960s resulted in the appearance of many dolphinaria around the world, making dolphins accessible to the public. Criticism and animal welfare
Animal welfare is the well-being of non-human animals. Formal standards of animal welfare vary between contexts, but are debated mostly by animal welfare groups, legislators, and academics. Animal welfare science uses measures such as longevity ...
laws forced many to close, although hundreds still exist around the world. In the United States, the best known are the SeaWorld
SeaWorld is an American theme park chain with headquarters in Orlando, Florida. It is a proprietor of marine mammal parks, oceanariums, animal theme parks, and rehabilitation centers owned by SeaWorld Parks & Entertainment (one park will be ...
marine mammal park
A marine mammal park (also known as marine animal park and sometimes oceanarium) is a commercial theme park or aquarium where marine mammals such as dolphins, beluga whales and sea lions are kept within water tanks and displayed to the public in ...
s.
In the Middle East the best known are Dolphin Bay at Atlantis, The Palm
Atlantis The Palm, Dubai is a luxury hotel resort located at the apex of the Palm Jumeirah in the United Arab Emirates. It was the first resort to be built on the island and is themed on the myth of Atlantis but includes distinct Arabian element ...
and the Dubai Dolphinarium
Dubai Dolphinarium is the first fully air-conditioned indoor dolphinarium in the Middle East, providing habitat to dolphins and seals, allowing the public to watch and interact with them through live shows and photo sessions. It is located in the c ...
.
Various species of dolphins are kept in captivity. These small cetaceans are more often than not kept in theme parks, such as SeaWorld
SeaWorld is an American theme park chain with headquarters in Orlando, Florida. It is a proprietor of marine mammal parks, oceanariums, animal theme parks, and rehabilitation centers owned by SeaWorld Parks & Entertainment (one park will be ...
, commonly known as a dolphinarium
A dolphinarium is an aquarium for dolphins. The dolphins are usually kept in a pool, though occasionally they may be kept in pens in the open sea, either for research or public performances. Some dolphinariums consist of one pool where dolphins pe ...
. Bottlenose dolphin
Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the common ...
s are the most common species of dolphin kept in dolphinariums as they are relatively easy to train, have a long lifespan in captivity and have a friendly appearance. Hundreds if not thousands of bottlenose dolphins live in captivity across the world, though exact numbers are hard to determine. Other species kept in captivity are spotted dolphins, false killer whale
The false killer whale (''Pseudorca crassidens'') is a species of oceanic dolphin that is the only extant representative of the genus ''Pseudorca''. It is found in oceans worldwide but mainly in tropical regions. It was first described in 1846 ...
s and common dolphin
The common dolphin (''Delphinus delphis'') is the most abundant cetacean in the world, with a global population of about six million. Despite this fact and its vernacular name, the common dolphin is not thought of as the archetypal dolphin, with ...
s, Commerson's dolphin
Commerson's dolphin (''Cephalorhynchus commersonii''), also referred to by the common names jacobita, skunk dolphin, piebald dolphin, panda dolphin, or tonina overa (in South America), is a small oceanic dolphin of the genus ''Cephalorhynchus'' ...
s, as well as rough-toothed dolphin
The rough-toothed dolphin (''Steno bredanensis'') is a species of dolphin that can be found in deep warm and tropical waters around the world.
The species was first described by Georges Cuvier in 1823. The genus name ''Steno'', of which this spe ...
s, but all in much lower numbers than the bottlenose dolphin. There are also fewer than ten pilot whale
Pilot whales are cetaceans belonging to the genus ''Globicephala''. The two extant species are the long-finned pilot whale (''G. melas'') and the short-finned pilot whale (''G. macrorhynchus''). The two are not readily distinguishable at sea, a ...
s, Amazon river dolphin
The Amazon river dolphin (''Inia geoffrensis''), also known as the boto, bufeo or pink river dolphin, is a species of toothed whale classified in the family Iniidae. Three subspecies are currently recognized: ''I. g. geoffrensis'' (Amazon river ...
s, Risso's dolphin
Risso's dolphin (''Grampus griseus'') is a dolphin, the only species of the genus ''Grampus''. Some of the closest related species to these dolphins include: pilot whales (''Globicephala'' spp.), pygmy killer whales (''Feresa attenuata''), melon ...
s, spinner dolphin
The spinner dolphin (''Stenella longirostris'') is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which it rotates around its longitudinal axis as it leaps through the air. It is a ...
s, or tucuxi
The tucuxi (''Sotalia fluviatilis''), alternatively known in Peru ''bufeo gris'' or ''bufeo negro'', is a species of freshwater dolphin found in the rivers of the Amazon basin. The word ''tucuxi'' is derived from the Tupi language word ''tuchuc ...
in captivity. An unusual and very rare hybrid
Hybrid may refer to:
Science
* Hybrid (biology), an offspring resulting from cross-breeding
** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species
** Hybridity, the property of a hybrid plant which is a union of two dif ...
dolphin, known as a wolphin
A wholphin (portmanteau of whale + dolphin) is an extremely rare cetacean hybrid born from a mating of a female common bottlenose dolphin (''Tursiops truncatus'') with a male false killer whale (''Pseudorca crassidens''). The name implies a h ...
, is kept at the Sea Life Park in Hawaii, which is a cross between a bottlenose dolphin and a false killer whale
The false killer whale (''Pseudorca crassidens'') is a species of oceanic dolphin that is the only extant representative of the genus ''Pseudorca''. It is found in oceans worldwide but mainly in tropical regions. It was first described in 1846 ...
.
The number of orca
The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only Extant taxon, extant species in the genus ''Orcinus'' and is recognizable by its black ...
s kept in captivity is very small, especially when compared to the number of bottlenose dolphins, with 60 captive orcas
A number of orcas, also called killer whales, are held in captivity by humans for breeding or performance purposes. The practice of capturing and displaying orcas in exhibitions began in the 1960s, and they soon became popular attractions at pub ...
being held in aquaria . The orca's intelligence
Intelligence has been defined in many ways: the capacity for abstraction, logic, understanding, self-awareness, learning, emotional knowledge, reasoning, planning, creativity, critical thinking, and problem-solving. More generally, it can b ...
, trainability, striking appearance, playfulness in captivity and sheer size have made it a popular exhibit at aquaria and aquatic theme parks. From 1976 to 1997, 55 whales were taken from the wild in Iceland, 19 from Japan, and three from Argentina. These figures exclude animals that died during capture. Live captures fell dramatically in the 1990s, and by 1999, about 40% of the 48 animals on display in the world were captive-born.
Organizations such as the Mote Marine Laboratory
Mote Marine Laboratory is an independent, nonprofit, marine research organization based on City Island in Sarasota, Florida, with additional campuses in eastern Sarasota County, Boca Grande, Florida, and the Florida Keys. Founded in 1955 by Eug ...
rescue and rehabilitate sick, wounded, stranded or orphaned dolphins while others, such as the Whale and Dolphin Conservation
Whale and Dolphin Conservation (WDC), formerly Whale and Dolphin Conservation Society in the UK, is a wildlife charity that is dedicated solely to the worldwide conservation and welfare of all whales, dolphins and porpoises (cetaceans). It has ...
and Hong Kong Dolphin Conservation Society
The Hong Kong Dolphin Conservation Society (HKDCS) (Traditional Chinese: 香港海豚保育學會) is a non-governmental organisation that is dedicated to the Conservation movement, conservation of whales, and dolphins and porpoises in Hong Kong ...
, work on dolphin conservation and welfare. India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
has declared the dolphin as its national aquatic animal in an attempt to protect the endangered
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inva ...
Ganges river dolphin
The Ganges river dolphin (''Platanista gangetica'') is a species of toothed whale classified in the family Platanistidae. It lives in the Ganges and related rivers of South Asia, namely in the countries of India, Nepal, and Bangladesh. It is rel ...
. The Vikramshila Gangetic Dolphin Sanctuary
Vikramshila Gangetic Dolphin Sanctuary is located in Bhagalpur District of Bihar, India. The sanctuary is a 60 kilometers stretch of the Ganges River from Sultanganj to Kahalgaon in Bhagalpur district. notified as Vikramshila Gangetic Dolphin Sanc ...
has been created in the Ganges
The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma ( )). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international river to which India, Bangladesh, Nepal and China are the riparian states." is ...
river for the protection of the animals.
Controversy
There is debate over the welfare of cetaceans in captivity, and often welfare can vary greatly dependent on the levels of care being provided at a particular facility. In the United States, facilities are regularly inspected by federal agencies to ensure that a high standard of welfare is maintained. Additionally, facilities can apply to become accredited by the Association of Zoos and Aquariums (AZA), which (for accreditation) requires "the highest standards of animal care and welfare in the world" to be achieved. Facilities such as SeaWorld and the Georgia Aquarium are accredited by the AZA. Organizations such as World Animal Protection
World Animal Protection, formerly The World Society for the Protection of Animals (WSPA) is an international non-profit animal rights organization that has been in operation since 1981. The charity describes its vision as: A world where animal ...
and the Whale and Dolphin Conservation
Whale and Dolphin Conservation (WDC), formerly Whale and Dolphin Conservation Society in the UK, is a wildlife charity that is dedicated solely to the worldwide conservation and welfare of all whales, dolphins and porpoises (cetaceans). It has ...
campaign against the practice of keeping them in captivity. In captivity, they often develop pathologies, such as the dorsal fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...
collapse seen in 60–90% of male orca. Captives have vastly reduced life expectancies, on average only living into their 20s, although there are examples of orcas living longer, including several over 30 years old, and two captive orcas, Corky II and Lolita, are in their mid-40s. In the wild, females who survive infancy live 46 years on average, and up to 70–80 years in rare cases. Wild males who survive infancy live 31 years on average, and up to 50–60 years. Captivity usually bears little resemblance to wild habitat, and captive whales' social groups are foreign to those found in the wild. Critics claim captive life is stressful due to these factors and the requirement to perform circus tricks that are not part of wild orca behavior. Wild orcas may travel up to in a day, and critics say the animals are too big and intelligent to be suitable for captivity. Captives occasionally act aggressively towards themselves, their tankmates, or humans, which critics say is a result of stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
.
Although dolphins generally interact well with humans, some attacks have occurred, most of them resulting in small injuries. Orca
The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only Extant taxon, extant species in the genus ''Orcinus'' and is recognizable by its black ...
s, the largest species of dolphin, have been involved in fatal attacks on humans in captivity. The record-holder of documented orca fatal attacks is a male named Tilikum, who lived at SeaWorld
SeaWorld is an American theme park chain with headquarters in Orlando, Florida. It is a proprietor of marine mammal parks, oceanariums, animal theme parks, and rehabilitation centers owned by SeaWorld Parks & Entertainment (one park will be ...
from 1992 until his death in 2017. Tilikum has played a role in the death of three people in three different incidents (1991, 1999 and 2010). Tilikum's behaviour sparked the production of the documentary ''Blackfish
Blackfish is a common name for the following species of fish, dolphins, and whales:
Fish
* Alaska blackfish, (''Dallia pectoralis''), an Esocidae from Alaska, Siberia and the Bering Sea islands
* Black fish (''Carassioides acuminatus'') a cyprin ...
'', which focuses on the consequences of keeping orcas in captivity. There are documented incidents in the wild, too, but none of them fatal.
Fatal attacks from other species are less common, but there is a registered occurrence off the coast of Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
in 1994, when a man died after being attacked by a bottlenose dolphin
Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the common ...
named Tião. Tião had suffered harassment by human visitors, including attempts to stick ice cream sticks down her blowhole. Non-fatal incidents occur more frequently, both in the wild and in captivity.
While dolphin attacks occur far less frequently than attacks by other sea animals, such as sharks
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorp ...
, some scientists are worried about the careless programs of human-dolphin interaction. Dr. Andrew J. Read, a biologist at the Duke University Marine Laboratory who studies dolphin attacks, points out that dolphins are large and wild predators, so people should be more careful when they interact with them.
Several scientists who have researched dolphin behaviour have proposed that dolphins' unusually high intelligence in comparison to other animals means that dolphins should be seen as non-human person
Personhood or personality is the status of being a person. Defining personhood is a controversial topic in philosophy and law and is closely tied with legal and political concepts of citizenship, equality, and liberty. According to law, only a leg ...
s who should have their own specific rights and that it is morally
Morality () is the differentiation of intentions, decisions and actions between those that are distinguished as proper (right) and those that are improper (wrong). Morality can be a body of standards or principles derived from a code of cond ...
unacceptable to keep them captive for entertainment purposes or to kill them either intentionally for consumption or unintentionally as by-catch. Four countries – Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
, Costa Rica
Costa Rica (, ; ; literally "Rich Coast"), officially the Republic of Costa Rica ( es, República de Costa Rica), is a country in the Central American region of North America, bordered by Nicaragua to the north, the Caribbean Sea to the no ...
, Hungary
Hungary ( hu, Magyarország ) is a landlocked country in Central Europe. Spanning of the Carpathian Basin, it is bordered by Slovakia to the north, Ukraine to the northeast, Romania to the east and southeast, Serbia to the south, Croatia a ...
, and India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
– have declared dolphins to be "non-human persons" and have banned the capture and import of live dolphins for entertainment.
Military
A number of militaries have employed dolphins for various purposes from finding mines to rescuing lost or trapped humans. The military use of dolphins drew scrutiny during the Vietnam War, when rumors circulated that the United States Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
was training dolphins to kill Vietnamese divers. The United States Navy denies that at any point dolphins were trained for combat. Dolphins are still being trained by the United States Navy for other tasks as part of the U.S. Navy Marine Mammal Program
The U.S. Navy Marine Mammal Program (NMMP) is a program administered by the U.S. Navy which studies the military use of marine mammals - principally bottlenose dolphins and California sea lions - and trains animals to perform tasks such as ship an ...
. The Russian military is believed to have closed its marine mammal program in the early 1990s. In 2000 the press reported that dolphins trained to kill by the Soviet Navy had been sold to Iran
Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...
.
The military is also interested in disguising underwater communications as artificial dolphin clicks.
Therapy
Dolphins are an increasingly popular choice of animal-assisted therapy
Animal-assisted therapy (AAT) is an alternative or complementary type of therapy that includes the use of animals in a treatment. The goal of this animal-assisted intervention is to improve a patient's social, emotional, or cognitive functionin ...
for psychological problems and developmental disabilities. For example, a 2005 study found dolphins an effective treatment for mild to moderate depression. This study was criticized on several grounds, including a lack of knowledge on whether dolphins are more effective than common pets. Review
A review is an evaluation of a publication, product, service, or company or a critical take on current affairs in literature, politics or culture. In addition to a critical evaluation, the review's author may assign the work a content rating, ...
s of this and other published dolphin-assisted therapy (DAT) studies have found important methodological flaws and have concluded that there is no compelling scientific evidence that DAT is a legitimate therapy or that it affords more than fleeting mood improvement.
Consumption
Cuisine
In some parts of the world, such as Taiji, Japan and the Faroe Islands
The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic island group and an autonomous territory of the Kingdom of Denmark.
They are located north-northwest of Scotland, and about halfway bet ...
, dolphins are traditionally considered as food, and are killed in harpoon
A harpoon is a long spear-like instrument and tool used in fishing, whaling, seal hunting, sealing, and other marine hunting to catch and injure large fish or marine mammals such as seals and whales. It accomplishes this task by impaling the t ...
or drive hunts.
Dolphin meat is consumed in a small number of countries worldwide, which include Japan and Peru
, image_flag = Flag of Peru.svg
, image_coat = Escudo nacional del Perú.svg
, other_symbol = Great Seal of the State
, other_symbol_type = Seal (emblem), National seal
, national_motto = "Fi ...
(where it is referred to as ''chancho marino'', or "sea pork"). While Japan may be the best-known and most controversial example, only a very small minority of the population has ever sampled it.
Dolphin meat is dense and such a dark shade of red as to appear black. Fat is located in a layer of blubber
Blubber is a thick layer of vascularized adipose tissue under the skin of all cetaceans, pinnipeds, penguins, and sirenians.
Description
Lipid-rich, collagen fiber-laced blubber comprises the hypodermis and covers the whole body, except for pa ...
between the meat and the skin. When dolphin meat is eaten in Japan, it is often cut into thin strips and eaten raw as ''sashimi
is a Japanese delicacy consisting of fresh raw fish or meat sliced into thin pieces and often eaten with soy sauce.
Origin
The word ''sashimi'' means "pierced body", i.e. "刺身" = ''sashimi'', where 刺 し = ''sashi'' (pierced, stuck) ...
'', garnished with onion and either horseradish
Horseradish (''Armoracia rusticana'', syn. ''Cochlearia armoracia'') is a perennial plant of the family Brassicaceae (which also includes mustard, wasabi, broccoli, cabbage, and radish). It is a root vegetable, cultivated and used worldwide ...
or grated garlic, much as with ''sashimi'' of whale
Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...
or horse meat
Horse meat forms a significant part of the culinary traditions of many countries, particularly in Eurasia. The eight countries that consume the most horse meat consume about 4.3 million horses a year. For the majority of humanity's early existe ...
(''basashi''). When cooked, dolphin meat is cut into bite-size cubes and then batter-fried or simmered in a ''miso
is a traditional Japanese seasoning. It is a thick paste produced by fermenting soybeans with salt and ''kōji'' (the fungus ''Aspergillus oryzae'') and sometimes rice, barley, seaweed, or other ingredients. It is used for sauces and spread ...
'' sauce with vegetables. Cooked dolphin meat has a flavor very similar to beef liver.
Health concerns
There have been human health concerns associated with the consumption of dolphin meat in Japan after tests showed that dolphin meat contained high levels of mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
.[ There are no known cases of ]mercury poisoning
Mercury poisoning is a type of metal poisoning due to exposure to mercury. Symptoms depend upon the type, dose, method, and duration of exposure. They may include muscle weakness, poor coordination, numbness in the hands and feet, skin rashe ...
as a result of consuming dolphin meat, though the government continues to monitor people in areas where dolphin meat consumption is high. The Japanese government recommends that children and pregnant women avoid eating dolphin meat on a regular basis.
Similar concerns exist with the consumption of dolphin meat in the Faroe Islands
The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic island group and an autonomous territory of the Kingdom of Denmark.
They are located north-northwest of Scotland, and about halfway bet ...
, where prenatal
Prenatal development () includes the development of the embryo and of the fetus during a viviparous animal's gestation. Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal devel ...
exposure to methylmercury
Methylmercury (sometimes methyl mercury) is an organometallic cation with the formula . It is the simplest organomercury compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It is a ...
and PCBs
Polychlorinated biphenyls (PCBs) are highly carcinogenic chemical compounds, formerly used in industrial and consumer products, whose production was banned in the United States by the Toxic Substances Control Act in 1979 and internationally by t ...
primarily from the consumption of pilot whale meat has resulted in neuropsychological deficits amongst children.
See also
* List of individual cetaceans
Cetaceans are the animals commonly known as whales, dolphins, and porpoises. This list includes individuals from real life or fiction, where fictional individuals are indicated by their source. It is arranged roughly taxonomically.
Baleen wh ...
*
References
Further reading
* Carwardine, M., ''Whales, Dolphins and Porpoises'', Dorling Kindersley, 2000. .
* Williams, Heathcote, ''Whale Nation'', New York, Harmony Books, 1988. .
External links
Conservation, research and news:
* De Rohan, Anuschka
"Why dolphins are deep thinkers"
''The Guardian
''The Guardian'' is a British daily newspaper. It was founded in 1821 as ''The Manchester Guardian'', and changed its name in 1959. Along with its sister papers ''The Observer'' and ''The Guardian Weekly'', ''The Guardian'' is part of the Gu ...
'', July 3, 2003.
The Dolphin Institute
The Oceania Project, Caring for Whales and Dolphins
Tursiops.org: Current Cetacean-related news
Photos:
{{Authority control
Animals that use echolocation
Extant Tortonian first appearances
Paraphyletic groups
National symbols of Anguilla
National symbols of Barbados
National symbols of Greece
National symbols of Malta
Mammal common names