Stingrays Essay, Research Paper

Stingrays Rays and their close relatives skates are common in Australian waters; there are at least 50 species that are found all around the Australian coastline. Rays are broad flat fish with a thin tail and have many characteristics of sharks, as they are related to them. For example they have no scales, swim bladder or bones; their skeleton is made up of cartilage. Unlike sharks they have blunt teeth, which allows them to crush the shells of shellfish. Stingrays usually live on the seabed where they often lie motionless. If they are trodden on or startled in any way they defend themselves with a sudden upward movement of their tail. The barb then drives the venom into the victim. Because of the size of the barb they are very dangerous-a man was once killed at Port Phillips Bay in Victoria when a stingray s barb punctured his heart. Under water divers have also suffered spines in vital organs such as the liver and lungs. Most stings occur on the leg though. Besides the immediate danger of serious physical injury from a stingrays barb there is also a high chance of infection, which could lead to death some days after the actual sting. This is often caused by bits of the sting that have remained in the wound. Rays have large wing-like pectoral fins and a narrow tail with one or more barbs at the end. They move by wave like movements of the pectoral fins. The largest and most well known ray, the manta or devil ray, moves by flapping its fins like a bird. These giant rays can grow to a width of seven metres and can weigh up to 1362 kg, although the smallest ray of the species only grows to about 60 cm across. They live in warm tropical waters along the equator. The devil ray gets its name from the two horn like objects known as cephalic fins on either side of their head. These strange looking horns are thought to be used to herd prey into its mouth. It feeds on plankton and small fish. Mantas are sometimes seen leaping out of the water, perhaps in an effort to rid themselves of parasites. It has few predators-only large sharks and killer whales are strong enough to defeat the devil ray. An old myth about the manta ray is that it envelopes divers in its wings and eats them but, despite its intimidating looks, the devil ray is totally harmless. Other species of harmless rays include the shovel nose ray, the fiddler ray and the brown stingray.

Another species of ray, the cowtail ray grows to a width of 1.5 metres. It is particularly dangerous to handle because unlike other rays its tail can reach all the way over its back and sting you, even if it is held by the front of its body. Although it may not look like it, the sawfish is a member of the ray family. Unlike other rays, its pectoral fins are only slightly exaggerated. The saw like snout is made up of enlarged rigid scales. To catch its prey it swings the saw around in schools of fish and then eats the stunned and injured fish. The common stingray or stingaree is found in river estuaries as well as in the ocean. This it the main species that is found at Underwater World. It is a pale sandy colour and is often hard to see, especially when covered by a thin layer of sand. The stingaree prefers to swim away from approaching humans but if it is stepped on it will use one of its barbs in self-defense. Another dangerous member of the ray family is the electric ray. This ray is capable of discharging 200 volts and may deliver 50 successive charges within 10 minutes.