Thursday, August 4, 2011

Life of Smooth Stingray

Life of Sea | Smooth Stingray (Dasyatis brevicaudata) | Smooth stingray is the largest of all Australian stingrays (Family Dasyatidae). It is also called Short tail stingray. This gives the fish its species name, brevicaudata, which comes from the Latin brevis, meaning 'short', and cauda meaning 'tail'. It is a bottom-dwelling species which is recorded from temperate waters. It lives in coastal waters and estuaries from shallow water down to about 170 m. Smooth stingray is mainly found in  bottom-dwelling in nature, inhabiting a variety of environments including brackish estuaries, sheltered bays and inlets, sandy flats, rocky reefs, and the outer continental shelf. Smooth stingray occurs in Australia, New Zealand and South Africa. In Australia, it is known from southern Queensland, around the south of the country and north to the central coast of Western Australia.

Smooth stingray is one of the largest rays in the world. It reaches a length of over 4 m from front to tail.  The disc diameter at birth is approximately 36 cm, but adults can reach a size of 2 m  in diameter, and weigh up to 350 kg. They have a thick body and bluntly-angular snout. The whip-like tail is thick at the base and - in adults - shorter than the body, with a small upper and a long lower caudal fanfold. There is a long, slender thorn just in front of the stings. There are two of these: a small front sting and a large rear sting, and they contain toxin glands. The upper side of the stingray is grey-brown or blue-grey, with pale-blue markings at the base of each pectoral fin, and the underside is plain white. They have flattened, plate-like teeth.

Smooth stingray searches for food both during the day and at night. It feeds mainly on benthic bony fishes and invertebrates, such as molluscs and crustaceans. The lateral line system on its underside allows it to detect the minute water jets produced by buried bivalves and spoon worms. Smooth stingray will often come close to fishing boats, tempted by the bait. They are inquisitive creatures, but not normally regarded as being aggressive, although they will raise their tail above their body like a scorpion if they feel threatened. They are a game fish, often caught by anglers, but need to be handled with extreme care since their barb can inflict a very severe – even fatal – wound. 

Smooth stingray is ovoviviparous. It means that fertilisation takes place inside the female’s body, and the embryos develop inside eggs, being nourished by the yolk until they hatch, and the mother gives birth to the larvae. This enormous stingray is one of the world’s largest rays and belongs to a group of species known as ‘bull rays’. Although it is non-aggressive, it has two toxic stings and a sharp thorn on its tail which can cause severe injury, or even death.  They have 2 stings, a small one in front one and the usual rear one considerably larger, which bear toxin glands. So, it needs to be treated with extreme caution.

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