Spinner Dolphins

The Spinner Dolphin, (sometimes referred to as the Long-snouted Dolphin), was discovered by John Gray in 1828 and is prevalent throughout the warm tropical oceans of the world. There are many species each of which displays its own unique variance or sub specie. The Spinner Dolphin is the most acrobatic dolphin, frequently jumping high out of the water and spinning around like a spinning top. It lives in the open ocean and feeds on the plentiful supplies of fish.

Spotting a Spinner
The Spinner Dolphin is dark grey with darker patches in the tail stock, back and throat. It often has a creamy white patch on its belly, all though this may vary. The beak is distinctively long and thin with a dark tip. The fins too are lengthy for dolphins of this size and the dorsal fin is distinctively erect. However this description has to be described as a little loose - the Spinner Dolphins markings are the most variable of all cetaceans.

The order Cetacean includes whales, dolphins and porpoises. Cetus is Latin and is used in biological terms to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek κῆτος (kētos), meaning "whale" or "any huge fish or sea monster". In Greek mythology the monster Perseus defeated was called Ceto, which is depicted by the constellation of Cetus. Cetology is the branch of marine science associated with the study of cetaceans.

Fully grown the Spinner can vary in overall length from as short as one hundred and thirty centimetres and can be as long as two hundred and thirty centimetres. Accordingly their weight may vary and adults may weigh between twenty three and seventy eight kilogram's. Female Spinner Dolphins reach maturity at four to seven years and males seven to ten years - the gestation period is ten months.

Playing
Spinner Dolphins congregate in pods or schools that can vary from a few to a great number, perhaps in the thousands. They are consistently acrobatic and enjoy riding in the bow waves of fast sea going vessels. They frequently jump out of the water and spin in the air and although it is not known why they perform such acrobatics, it has been suggested that they may be communicating via echolocation through the bubbles created by exit and re-entry. It may also be simply play-acting, individuals have been spotted completing at least fourteen spinning jumps in quick succession.

Communicating
Echolocation sounds enable dolphins to track objects in dim or dark water and to see much further than their eyes allow. The complex array of whistle sounds are the way the animals talk to one another. Spinner Dolphins may even identify themselves with sounds they make while trailing bubbles from their blowholes - these are known as signature whistles. Spinner Dolphins also communicate by slapping the water with various body parts. `Nose-outs' occur when the beak is thrust from the surface, this action is commonly used when the pod is emerging from a rest period. `Tail slaps' are often used to indicate impending danger or to signal a dive. `Head slaps' and `side slaps', and `back slaps' are most frequently seen as the school begins to pick up speed. Last, and most spectacular, are the spins themselves. Many animals spin repeatedly, with each spin tending to get smaller and smaller, finally finishing up with an emphatic side slap.

The power of the spin may be picked up through the Dolphins echolocation ability and may be the real purpose of the spin. Spinner dolphins maximize the effect of this splash by twisting around to land in a belly-flop, or back-flop. Spins are most frequently performed while the school is spread out across the water. A spinning dolphin may be alerting other members of the group to a change of direction or simply indicating current position. The effect of many dolphins spinning and leaping at once determines the size, speed and direction of the school, which scientists call the envelope of the school.

Hunters of the night
Dolphins do most of their hunting at night as the `scattering layer' of marine life composed of fish, jellyfish, krill or euphausiids, squid, shell-less snails, as well as copepods rises toward the surface to feed on microscopic plant material having spent the day at depth. Before plunging into the layer, the pod of dolphins gather together realizing that they are about to embark on a dangerous expedition. The dolphins take a great risk because other predators have gathered as well, such as sharks, which are natural predators of dolphins. The spinners form small subgroups and spread out across the sea. Time after time, the dolphins dive down into the utter darkness at eight hundred feet, or more. They do not use their teeth to chew, but rather to grasp and immobilize their prey.

Despite being separated by several miles of water, the Dolphins coordinates their activities through sound and through spinning, which reaches an explosive crescendo in the darkness of night. Using their echolocation, the spinners scan the darkness and, using their whistles, they call members of the school back together and can unite for defence. The following day, the spinners regroup - well-fed they relocate in the shelter of coastal inlets or nearby islands.

Endangered
Spinner Dolphins occur in pelagic, (open seas), tropical waters in all the world's major oceans and although they mainly live in the open ocean, they are sometimes found near the shores of tropical islands. Their greatest population density occurs between the Tropics of Cancer and Capricorn. The total population is unknown, but has certainly been dramatically reduced by fishing activity and is still regarded as endangered.

It has been estimated that up to two million Dolphins were killed in the thirty years after purse seine fishing for tuna was introduced in the 1950s. The process killed probably half of all Eastern Spinner Dolphins.

Purse seine Fishing
Purse seine is a preferred technique for capturing fish species which gather close to the surface before they swim up rivers and streams to spawn - boats equipped with purse seines are called purse seiners. A common type of seine is a purse seine, named because along the bottom are a number of rings. A rope passes through all the rings, and when pulled, draws the rings close to one another, preventing the fish from swimming down to escape the net. This operation is similar to a traditional style purse, which has a drawstring.

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