Stingray

Stingrays
	Bluespotted stingray, Taeniura lymma
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
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 (about 14.6 inches). 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.^[1] 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.

Feeding habits

Stingrays are flat so as to hide on the depths of the sea. They ruffle up the sand and hide beneath it. 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.

Stinging mechanism

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 whipped up. This attack is normally ineffective against their main predator, sharks.^[2] Humans are usually stung in the foot region (depending on the size of the stingray); it is also possible, although less likely, to be stung by brushing against the stinger. The stinger often breaks off in the wound, 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 later infection from bacteria on parts of the stinger left in the wound. Immediate injuries to humans include, but are not limited to: poisoning, punctures, severed arteries and possibly death. Fatal stings, such as that which killed Australian naturalist and television personality Steve Irwin in September 2006,^[3] are extremely rare.

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.^[4] 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 surgical exploration is often required to remove any barb fragments remaining in the wound. Following cleaning, a radiograph is helpful to confirm removal of all the fragments.^[5] However, not all remnants are radio-opaque; ultrasound imaging is useful in difficult cases.

Reproduction

Mating season occurs in the winter. When a male is courting a female, he will follow her closely, biting at her pectoral disc. During mating, the male will go on top of the female (his belly on her back) and put one of his claspers into her vent.[1]

Most rays are viviparous, bearing live young in "litters" of five to ten. The female holds the embryos in the womb without a placenta. Instead, the embryos absorb nutrients from a yolk sac, and after the sac is depleted the mother provides uterine milk. [2]

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. For example, it is grilled using charcoal in Malaysia and is a popular dish known as Ikan Bakar. 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.

In Iceland, eating pickled stingray ("kæst skata") on December 23 is an old tradition.^[6] The Icelanders are divided into two groups on this day, those who love the stingray, and those who hate the putrid smell of pickled fish.

Viewing

File:Stingray-buried-in-sand.jpg

Stingrays can be seen burrowing into the sand just yards away from tourists at Stingray City.

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.

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.

Many Tahitiian island resorts regularly offer guests the chance to "feed the stingrays and sharks". This consists of taking a boat to the outer lagoon reefs then standing in waist-high water while habituated stingrays swarm around, pressing right up against you seeking food from your hand or tossed into the water. The boat owners also "call in" sharks, which when they arrive from the ocean swoop through the shallow water above the reef and snatch food offered to them.

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 spines on the rays are snipped off with a pair of pliers. The tip of the spine 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 and the North Carolina Aquarium in Manteo, NC, allow 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, as does Underwater Adventures Aquarium at the Mall of America in Bloomington, Minnesota.

In 2006, the Tampa Bay Devil Rays added a 35 foot (10.7 m), 10 000 gallon (38 000 L), touch tank in their stadium where fans get a chance to interact with dozens of rays.^[7]

Danger to humans

Perhaps the most famous stingray-related injury is the one that resulted in Steve Irwin's death. He was pierced in the chest with a stingray spine while snorkeling in Australia. He immediately pulled it out, and he was dead by the time his team had brought him to a hospital. This high-profile death resulted in a backlash against stingrays.

Ben Cropp, an Australian documentary filmmaker, has also been stabbed in the chest by a stingray. [3] However, he survived.

Another man, this time in Florida, was also stabbed in the chest. The ray had jumped into the boat, and when he tried to remove the ray it latched on to him. He left the barb in and piloted the boat to shore, where he called 911. He survived.

Yet another man was stabbed in the chest in Fiji. This man was on vacation from Australia. He swam over a large stingray and was stung in the chest. He died the next day. [4]

These chest-puncturing wounds are not typical, and most injuries that humans get from stingrays are because they step on one by accident. Stingrays are often semi-buried in the sand so they are easy to overlook. It is also possible to be bitten, but this is also a rare type of injury, since the mouth is on the bottom side of the ray.