Information On Dolphins

 

Dolphin Information
Planet Dolphin

Family: Delphinidae
thirty-two species in 17 genera
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Distribution: all oceans.
Habitat: mostly coastal shallows but some open-sea.

Longevity: up to 50-100 years (Killer whale).

The dolphins intelligence and developed social organization are equaled only by the primates, maybe only by man, while their general friendliness and lack of aggression are compared favorably with man. dolphin1

Specie include: Bottled-nose (tursiops truncatus), Bridled dolphin (stenella attenuata), Bommon dolphin (delpinus delphis), False killer whale (pseudorca crassidens), Guiana dolphin (sotalia guianensis), Humpedback dolphin (sousa teuszii), Killer whale (orcinus orca) Melon-headed whale (peponocephala electra), Risso's dolphin (grampus griseus), Spinner dolphin (stenella longirostris), Tucuxi (sotalia fluviatilis)

Size: Head to tail length from 1.2m (3.5ft) in Heaviside's dolphin to 7m (23ft) in the Killer whale: weight from 40kg (88lbs) in Heaviside's dolphin to 4-5 tons in the Killer whale.

Most dolphins are small to medium-sized animals with a well-developed beak and a central sickle-shaped dorsal fin curving backwards. They have a single crescent-shaped blowhole, with the concave side facing forwards on top of the head, and they have functioned well-separated teeth in both jaws (between 10 and 224 but most between 100 and 200).

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Most Delphinids have a forehead melon although this is indistinct in some species, for example the Guiana dolphin and tucuxi, absent in Cephalorhynchus species, pronounced and rounded to form an indistinct beak in Risso's dolphin and the two species of pilot whales, and tapered to form a blunt snout in Killer and False whales. Killers also have rounded paddle-shaped flippers, whereas the pilot whales and False killer have narrow elongated flippers. The aforementioned species are not closely related to each other but several genera, particularly Delphinus, Stenella, Sousa and Sotalia, contain species which are indistinct from each other.

The extensive differences in color patterns between species has been variously categorized. One classification recognizes three types: uniform (plain or even marked), patched (with clearly colored pigmented markings), and counter-shaded (black and white).

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The anatomical differences between dolphins relate partly to differences in diet. Those species with more rounded foreheads, blunt beaks, and often reduced detention, feed primarily upon squid, or, in the case of the Killer whale, the diet also includes marine mammals and birds. The development of the cranial region may be an adaptation for receiving and focusing acoustical signals to obtain an accurate picture of the location of their agile, fast-moving prey. The other members of the family feed mostly on fish. Some feed close to shore while others feed out to sea.

Most dolphins at least occasionally feed upon squid, and even shrimps. That, having been said, makes it difficult to understand the extent of competition among dolphin species. The more pelagic dolphin species tend to travel in herds of 1000 or more, whose members may cooperate in the shoaling of fish. Inshore species usually form smaller herds of 2-12 individuals. While foraging, dolphin schools often spread out to form a band, varying in size.

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Until recently, most information about dolphins was gathered from dead animals that had come ashore on the beaches. Most had died at sea and washed ashore, but some strand while alive, and such incidents are most conspicuous when groups of animals strand together, which is most prevalent among pilot whales and False killers. The cause of strandings by live animals is not known. Some theories are, infection of the inner ear which effects echolocation abilities, the effects of upsetting sounds, explosions and the like, herds following a old and/or sick leader, disorientation from unknown territory.

Gestation is 10 to 12 months (16 months in pilot whales and Risso's dolphin). Sexual behavior in dolphins occurs throughiut the year although there is usually a peak in calving during the summer months. The single calf remains with the mother for several months, with lactating lasting up to 1.5 to 2 years. This suggests that many species breed at minimal intervals of 2-3 years. The age of sexual maturity ranges between 5 years (Common dolphin) and 16 years (Killer whale), with most species breeding at about 8-10 years old.

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Many species undergo seasonal migrations in search of food; these are usually offshore-inshore movements but may be latitudinal. If discrete breeding areas exist, they have rarely been identified, although it is probable that they are in deeped offshore waters where there are calmer waters.

Dolphins are gregarious, with some species forming herds of a thousand or more, but these generally occur during long-distance movements or when concentrated at food sources. There is no evidence of well-developed social organization typical of primates.

The Future of the Dolphin

Dolphins often congregate in numbers of up to 2000 at feeding areas, which often coincides with human fisheries, resulting in conflicts of interest. Gill-nets, laid to catch salmon or capelin, also catch and drown dolphins. Inshore porpoises are most at risk.

A less obvious threat to dolphins comes from inshore pollution by toxic chemicals, and acoustic disturbances from boats. Although hunting dolphin is on the decline, it still exists in areas of the Black Sea.

 


 


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