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Stingray

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For other uses, see Stingray (disambiguation).

Stingrays
Bluespotted ribbontail ray, Taeniura lymma
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Rajiformes
Family: Dasyatidae
Genera

Dasyatis
Himantura
Pastinachus
Pteroplatytrygon
Taeniura
Urogymnus
See text for species.

Dasyatidae is a family of rays, cartilaginous marine fishes, related to skates and sharks.

Dasyatids are common in tropical coastal waters throughout the world, and there are fresh water species in Asia (Himantura sp.), Africa, and Florida (Dasyatis sabina). Most dasyatids are neither threatened nor endangered. The species of the genera Potamotrygon, Paratrygon, and Plesiotrygon are all endemic to the freshwaters of South America.

Dasyatids swim with a "flying" motion, propelled by motion of their large pectoral wings (commonly mistaken as "fins"). Their stinger is a razor-sharp, barbed or serrated cartilaginous spine which grows from the ray's whip-like tail (like a fingernail), and can grow as long as 37 cm. On the underside of the spine are two grooves containing venom-secreting glandular tissue. The entire spine is covered with a thin layer of skin called the integumentary sheath, in which venom is concentrated. This gives them their common name of stingrays, but the name can also be used to refer to any poisonous ray.

Some adult rays may be no larger than a human palm, while other species, like the short-tail stingray, may have a body of six feet in diameter, and an overall length, including their tail, of fourteen feet. Like other rays, dasyatids are viviparous, bearing live young in "litters" of five to ten.

Feeding habits

Underside of freshwater ray showing mouth

Since their eyes are on top of their body and their mouths on the bottom, stingrays cannot see their prey. Instead, they use the sense of smell and electro-receptors, similar to those of the shark. They feed primarily on molluscs and crustaceans and occasionally on small fish. Their mouths contain powerful, shell-crushing teeth. Rays settle on the bottom while feeding, sometimes leaving only their eyes and tail visible.

Aggression

Dasyatids generally do not attack aggressively or even actively defend themselves. When threatened, their primary reaction is to swim away. However, when they are attacked by predators or stepped on, the barbed stinger in their tail is mechanically whipped up. This attack is normally ineffective against their main predator, sharks. Humans are usually stung in the foot; it is also possible, although less likely, to be stung by brushing against the stinger. The stinger may break off, which is non-fatal to the stingray, and will be regrown. Contact with the stinger causes local trauma (from the cut itself), pain and swelling from the venom, and possible infection from parts of the stinger left in the wound. Injuries to humans include, but are not limited to: poisoning, punctures, severed arteries and possible death. Fatal stings, such as that which killed Australian naturalist and television personality Steve Irwin in September 2006, are extremely rare, and in Irwin's case, it was the massive wound to the heart rather than just the venom that caused his death.. Up to 1996, worldwide known deaths from stingray barb injuries numbered 17.

Treatment for stings includes application of near-scalding water, which helps ease pain by denaturing the complex venom protein, and antibiotics. Immediate injection of local anaesthetic in and around the wound is very helpful, as is the use of adjunct opiates such as intramuscular pethidine. Local anaesthetic brings almost instant relief for several hours. Other possible pain remedies include papain (papaya extract, contained in unseasoned powdered meat tenderizer), which may break down the protein of the toxins, although this may be more appropriate for jellyfish and similar stings. Folklore incorrectly holds that one should urinate on the stung area; in actuality, urine and vinegar are not effective treatments. Pain normally lasts up to 48 hours, but is most severe in the first 30–60 minutes and may be accompanied by nausea, fatigue, headaches, fever and chills. All stingray injuries should be medically assessed; the wound needs to be thoroughly cleaned and often surgical exploration is required to remove any barb fragments remaining in the wound. Following cleaning a radiograph is helpful to confirm removal of all the fragments.

Stingrays are a large part of the Melbourne Aquarium

As food

Rays may be caught on a fishing line using small crabs as bait, and are often caught accidentally; they may also be speared from above. They are edible. Small rays may be cooked similarly to other fish, typically grilled or battered and fried. Whilst not independently valuable as a food source, the stingray's capacity to damage shellfishing grounds can lead to bounties being placed on their removal.

Stingray recipes abound throughout the world, with dried forms of the wings being most common. Generally, the most prized parts of the stingray are the wings, the "cheek" (the area surrounding the eyes) and the liver. The rest of the ray is considered too rubbery to have any culinary uses.

Viewing

Stingrays are usually very docile creatures. The customary reaction of the stingray is to immediately flee the vicinity of a disturbance. Nevertheless, certain larger species are located in waters where they are easily excitable due to possible attacks from feeding sharks and should be approached with caution, as the stingray's defensive reflex and effort to flee may result in human contact with the stinger, resulting in serious injury or even (though rarely) death.

Dasyatids are not normally visible to swimmers, but divers and snorkelers may find them in shallow sandy waters, more so when the water is unseasonably warm.

In the Cayman Islands, there are several dive sites called Stingray City, Grand Cayman, where divers and snorkelers can swim with large southern stingrays (Dasyatis americana) and feed them by hand.

There is also a "Stingray City" in the sea surrounding the Caribbean island of Antigua. It consists of a large, shallow reserve where the rays live and snorkelling is possible, as the rays there are said to be very friendly.

In Belize off the island of Ambergris Caye there is a popular marine sanctuary called Hol Chan. Here divers and snorkelers often gather to watch stingrays and nurse sharks who are drawn to the area by tour operators who feed the animals.

Most major aquariums feature stingrays, including the National Baltimore Aquarium and the Tennessee Aquarium in Chattanooga. Where there are stingray touch tanks where visitors can "pet" rays or when show divers routinely hand feed rays in giant saltwater exhibits, for diver and visitor safety the barbs on the rays are snipped off with a pair of pliers. The tip of the barb is then presented as a harmless stub that can't penetrate the skin of visitors or divers who routinely handle the docile rays.

The Atlantis Paradise Island Hotel houses many eagle rays, sting rays and one manta ray. The rays are often coexhibited with other marine life, such as the Caribbean reef shark. The Georgia Aquarium allows petting of southern stingrays in their "Georgia Explorer" exhibit. Similarly, visitors may use two fingers at a time to touch rays (with sting removed) and related guitarfish in outdoor exhibits at the Aquarium of the Pacific in Long Beach, California. Petting stingrays is also permitted in a special tank at the Blue Planet Aquarium, Ellesmere Port, England. Likewise, the Mote Marine Aquarium in Sarasota, Florida, allows visitors to pet a variety of rays in a controlled tank setting. Coral World Marine Park in St. Thomas, USVI, even allows supervised feeding of southern stingrays by visitors.

In 2006, the Tampa Bay Devil Rays added a 35 foot, 10000 gallon, touch tank in their stadium where fans get a chance to interact with dozens of rays.

Small rays and other fishes can be petted in a "tactile tank" at Nausicaä, a large aquarium park in Boulogne-sur-Mer, on the English Channel coast in northern France. One ray has been known to be so friendly it tried to expose its entire ventral surface, ending up toppling over backward.

Species

A typically-placid stingray idling at the bottom of the sea, with unusually clear water, in Eilat, Israel.
Stingray City in Grand Cayman allows swimmers, snorkelers, and divers to swim and feed stingrays.

There are about seventy species in six genera:

References

  1. Meyer P (1997). "Stingray injuries". Wilderness Environ Med. 8 (1): 24–8. PMID 11990133.
  2. "Stingray City - About Stingrays". Caribbean Magazine.
  3. "'Crocodile hunter' Steve Irwin killed by a stingray". The Guardian. September 4, 2006. {{cite news}}: Check date values in: |date= (help)
  4. Surf Life Saving Australia (September 4, 2006). "Information on Stingrays". {{cite web}}: Check date values in: |date= (help)
  5. Stingray Injuries in the Sea of Cortez
  6. Flint D, Sugrue W (1999). "Stingray injuries: a lesson in debridement". N Z Med J. 112 (1086): 137–8. PMID 10340692.
  7. Last, Manjaji-Matsumoto & Kailola (2006). "Himantura hortlei n. sp., a new species of whipray (Myliobatiformes: Dasyatidae) from Irian Jaya, Indonesia" (PDF). Zootaxa. 1239: 19–34.
  8. Last, Manjaji & Yearsley (2005). "Pastinachus solocirostris sp. nov., a new species of Stingray (Elasmobranchii: Myliobatiformes) from the Indo-Malay Archipelago" (PDF). Zootaxa. 1040: 1–16.

Bibliography

External link

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