Dolphin
[9] In common usage, the term whale is used only for the larger cetacean species,[10] while the smaller ones with a beaked or longer nose are considered dolphins.
Two wholphins currently live at the Sea Life Park in Hawaii; the first was born in 1985 from a male false killer whale and a female bottlenose.
[30] Today, the closest living relatives of cetaceans are the hippopotamuses; these share a semi-aquatic ancestor that branched off from other artiodactyls some 60 million years ago.
The skin of dolphins is specialized to satisfy specific requirements, including protection, fat storage, heat regulation, and sensory perception.
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 .
[46] 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 thermal windows that lack blubber, are not fully insulated and are somewhat thin and highly vascularized, including the dorsal fin, flukes, and flippers.
[citation needed] A study of a Pacific white-sided dolphin in an aquarium found fast burst acceleration, with the individual being able with 5 strokes (2.5 fluke beats) to go from 5.0 m s-1 to 8.7 m s-1 in 0.7 seconds.
[50] The fusing of the neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, which means most dolphins are unable to turn their heads.
They lack short wavelength sensitive visual pigments in their cone cells, indicating a more limited capacity for color vision than most mammals.
The dolphin Moko in New Zealand has been observed guiding a female pygmy sperm whale together with her calf out of shallow water where they had stranded several times.
[94] Dolphins are known to display non-reproductive sexual behavior, engaging in masturbation,[95] stimulation of the genital area of other individuals using the rostrum or flippers, and homosexual contact.
[137] This started in 1988 when a female named Billie was rescued after becoming trapped in a polluted marina,[139] and spent two weeks recuperating with captive dolphins.
[140] A 2018 study by Mike Rossley et al. suggested:[136]Social learning is the most likely mechanism for the introduction and spread of this unusual behaviour, which has no known adaptive function.
[145][146] Symptoms of infection are often a severe combination of pneumonia, encephalitis and damage to the immune system, which greatly impair the cetacean's ability to swim and stay afloat unassisted.
[154] Pesticides, heavy metals, plastics, and other industrial and agricultural pollutants that do not disintegrate rapidly in the environment concentrate in predators such as dolphins.
[157][158] In some parts of the world, such as Taiji in Japan and the Faroe Islands, dolphins are traditionally considered food and are killed in harpoon or drive hunts.
Because of this, prey resources have been reduced causing a steep decline in the short-beaked common dolphin Mediterranean subpopulation, which was deemed endangered in 2003.
[170] At the Shark Bay World Heritage Area in Western Australia, the local Indo-Pacific bottlenose dolphin population had a significant decline after a marine heatwave in 2011.
During the 2009 excavations of a major Mycenaean city at Iklaina, a striking fragment of a wall painting came to light, depicting a ship with three human figures and dolphins.
A dolphin rescued the poet Arion from drowning and carried him safe to land, at Cape Matapan, a promontory forming the southernmost point of the Peloponnesus.
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.
There are comparatively few surviving myths of dolphins in Polynesian cultures, in spite of their maritime traditions and reverence of other marine animals such as sharks and seabirds; unlike these, they are more often perceived as food than as totemic symbols.
Dolphins are most clearly represented in Rapa Nui Rongorongo, and in the traditions of the Caroline Islands they are depicted similarly to the Boto, being sexually active shapeshifters.
[190] The orca's intelligence, trainability, striking appearance, playfulness in captivity and sheer size have made it a popular exhibit at aquaria and aquatic theme parks.
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.
[215] In some parts of the world, such as Taiji, Japan and the Faroe Islands, dolphins are traditionally considered as food, and are killed in harpoon or drive hunts.
[159] Dolphin meat is consumed in a small number of countries worldwide, which include Japan[216] and Peru (where it is referred to as chancho marino, or "sea pork").
[220] The Faroe Islands population was exposed to methylmercury largely from contaminated pilot whale meat, which contained very high levels of about 2 mg methylmercury/kg.
The study of about 900 Faroese children showed that prenatal exposure to methylmercury resulted in neuropsychological deficits at 7 years of ageConservation, research and news: Photos:
