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The Rays and Manta Ray
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Manta Ray: The Good Devil
For centuries it was thought that the manta ray, or "devilfish," was an evil ocean beast capable of destroying fishing boats and devouring people. In fact, the manta ray is one of the gentlest creatures in the sea whose only wish, it seems, is to float peacefully in the water sucking in mouthfuls of water in search of its favorite food -- plankton.
It's understandable why people have been frightened by this tremendous fish. The manta ray is the largest member of the and can measure up to 19 feet long and weigh as much as 2,300 pounds. Some manta rays have been caught that measure an unbelievable 23 feet across. This giant sea creature takes its name from the Spanish word "manta" meaning blanket. With its enormous black fins extended, the manta ray really does look like a huge floating blanket.
Manta rays live mainly in tropical waters and feed on zooplankton, small fish and crustaceans. Like other rays, the Manta has a skeleton made out of cartilage instead of bone, and its nostrils, mouth and gill slits are ventral, or located on its underside. Manta rays can be found browsing through sandflats in search of food or, sometimes, leaping clear out of the water. Manta rays give birth to live young. When their babies are born they are wrapped up in their little wing flaps like pigs in a blanket. Baby manta rays are called "pups."
Manta rays usually swim in pairs, and although they seem frightening, manta rays are so gentle that many will even let humans pet them. Some experienced divers have actually taken rides on the backs of these beautiful, harmless fish.
Despite their size, manta rays are usually graceful and tend to be tolerant with divers.
Manta rays were once called devil fish by sailors who saw large "horns" extending forward from their heads. These horns turned out to be ingenuous scoopers which, when unfurled, guide plankton into the manta’s mouth. Manta wingspans can reach up to 20 feet, and they glide though the water like birds. Both gentle and graceful, they have become a favorite attraction for divers. Their range is circumtropical, with sightings in the Atlantic from as far north as New England and south to Brazil. Mantas prefer plankton-rich waters and are regular visitors to a few select locations. In the winter, mantas visit San Benedicto Island, south of Cabo San Lucas, Mexico. Here, they glide past a pinnacle called The Boiler hoping to take advantage of the resident cleaner fish. Mantas also hang out in Yap, Micronesia at Manta Ridge, another cleaning station. From March through July, mantas visit the island of Tobago, feeding in the rich waters fed by the Orinoco estuary in South America. On Hawaii’s Kona Coast, mantas are drawn each evening to the lights of a large hotel. Night divers watch as the mantas feed on the plankton that is attracted by the lights. [from: http://www.letsfindout.com/subjects/undersea/rfimanta.html ]
devil ray
also called MANTA RAY, any of several genera of marine rays comprising the family Mobulidae (class Selachii). Flattened, and wider than they are long, devil rays have fleshy, enlarged pectoral fins that look like wings; extensions of these fins, looking like devils' horns, project as the cephalic fins from the front of the head. Devil rays have long, whiplike tails provided, in some species, with one or more stinging spines.
Devil rays, related to sharks and skates, are found in warm waters along continents and islands. They swim at or near the surface, propelling themselves by flapping their pectoral fins and, at times, leaping or somersaulting out of the water. They feed on plankton and small fishes that they sweep into their mouths with their cephalic fins.
Atlantic manta (Manta birostris)
The smallest of the devil rays, species Mobula diabolis of Australia, grows to no more than 60 cm (2 feet) across, but the , or giant devil ray (Manta birostris; see ), largest of the family, may grow to more than 7 m (23 feet) wide. The Atlantic manta is a well-known species, brown or black in colour and very powerful, but inoffensive. It does not, old tales to the contrary, envelop pearl divers and devour them
[from "devil ray" Encyclopędia Britannica Online http://www.eb.com:180/bol/topic?eu=30645&sctn=1 [Accessed April 19, 1999]. ]
Habitat: Manta rays typically are found in the open ocean, but will occasionally pass over reefs.
Average adult size: Adults can grow to be more than 20 feet across, from wing-tip to wing-tip.
Natural history: Manta rays swim near the surface of the open sea. Their bad reputation as a "devilfish" is undeserved. Hardly man-eaters, they cruise slowly through the water, feeding on microscopic plankton. The manta uses the fins on either side of its head to herd plankton into its mouth. It will sometimes swim somersaults in the water to take advantage of a particularly rich area of plankton. Mantas are known to jump out of the water or "breach." They will have one or two babies per "litter."
Range: Found in Brazil north to Bermuda.
Pictures of Mantas
http://www.big.or.jp/~ishigaki/manta/E_manta.html
http://emoo.imaginary.com:4243/objbrowse/~manta
Rays
any of the cartilaginous fishes of the order Batoidei, related to and placed with them in the class Chondrichthyes (or Selachii). The order includes 300 to 350 species.
Rays are distinguished from sharks by a flattened, disklike body, with the five gill openings and the mouth generally located on the underside. Rays are further distinguished from sharks by their greatly enlarged, winglike pectoral fins, which extend forward along the sides of the head above the gill openings. Many rays swim and breathe differently from sharks, propelling themselves with their pectoral fins and taking in water for respiration through large openings (spiracles) on the upper surface of the head, rather than through the mouth. The ray's tail is generally long and slender and in many species bears one or more sharp, saw-edged, venomous spines that can be used to inflict painful wounds.
Rays are predominantly marine and are found in all oceans. Many are slow-moving bottom dwellers. feed on plankton and small animals; others take various fishes and invertebrates, sometimes damaging commercially valuable shellfish beds. Other than skates, most or possibly all rays bear living young. Fertilization is internal, the male introducing sperm into the female by means of special copulatory organs (claspers) that are the modified edges of the pelvic fins.
Rays can be classified into the following groups: electric rays, sawfishes, skates, and various families of rays that have slender, whiplike tails equipped with spines and that are all-inclusively called , or whip-tailed rays.
The (suborder Torpedinoidei) are distinguished by large paired electric organs between the pectoral fins and the head, with which they can give powerful shocks either for defensive purposes or to kill prey. The electric rays have a smooth and naked skin; the head and trunk with the pectoral fins form a circular disk, and the tail is short and stout. About 20 species are known to inhabit warm seas, with some reaching a weight of 200 pounds (90 kg).
All other types of rays, which lack electric organs, generally have a rough skin, often bearing strong spines. The (family Pristidae) have a snout that is modified into a long blade possessing a series of strong teeth on each side. About six species are known from warm seas, frequenting sandy shores and estuaries.
In the (suborder Rajoidei), the large pectoral fins extend to the snout and backward, stopping abruptly at the base of a slender tail. In contrast to other rays, skates produce eggs; these are large and oblong in shape with dark, leathery shells having a tendril at each corner by which they become fastened to seaweed or other objects. Skates lack the long, slender barbed spine that distinguishes stingrays. The most widespread skates belong to the genus Raja of the family Rajidae.
The remaining rays comprise the suborder Myliobatoidei and consist of whip-tailed rays (family Dasyatidae), butterfly rays (Gymnuridae), stingrays (Urolophidae), eagle rays (Myliobatidae), devil rays (or mantas; Mobulidae), and cow-nosed rays (Rhinopteridae). Common to the rays of all these families is a long, slender, whiplike tail that usually has a barbed spine connected with a poison gland; this spine is capable of inflicting serious wounds and is a dangerous weapon when the tail is lashed. Almost all of these rays are inhabitants of warm seas, except for a few species of stingray that live in the rivers of South America. (See .)
The are a group of fishes that are closely related to the rays and are either classified as a separate order (Rhinobatiformes) or as a suborder (Rhinobatoidei) of the ray order (Batoidei).
The majority of batoid fishes (members of the order Batoidei; i.e., and allies) are bottom dwellers, preying on other animals on or near the sea floor. (Rhynchobatidae and Rhinobatidae), butterfly rays (Gymnuridae), eagle rays (Mylobatidae), and cow-nosed rays (Rhinopteridae) feed on invertebrates, principally mollusks and crustaceans. Whip-tailed rays (Dasyatidae) use their broad pectoral fins to dig shellfish from sand or mud. Skates lie on the bottom, often partially buried, and rise in pursuit of such active prey as herring, trapping the victims by swimming over and then settling upon them, a practice facilitated by the skates' habit of hunting at night.
(Torpedinidae) are characteristically bottom fishes of sluggish habits. They feed on invertebrates and fish, which may be stunned by shocks produced from the formidable electric organs. With their electricity and widely extensible jaws, these rays are capable of taking very active fishes, such as flounder, eel, salmon, and dogfish. Shallow-water electric rays have been observed to trap fishes by suddenly raising the front of the body disk, while keeping the margins down, thereby forming a cavity into which the prey is drawn by the powerful inrush of water.
Most of the (seven recognized families of the suborder Myliobatoidea, which includes all of the typical rays) swim gracefully, with undulations of the broad, winglike pectoral fins. Some species, especially the eagle rays, frequently swim near the surface and even jump clear of the water, skimming a short distance through the air.
(From Seaworld info sheets)
The wingspan, or disc-size, of a southern stingray (Dasyatis americana) such as the one shown here can reach up to 1.5 m (5 ft.).
All rays belong to the superorder Batoidea, which includes stingrays, electric rays, skates, guitarfish, and sawfish. Like sharks—their close relatives—batoids have skeletons made of tough connective tissue called cartilage. About 480 species of batoids are distributed worldwide, particularly in warm and temperate climates, and are found in oceans, estuaries, freshwater streams, lagoons, lakes, shallow offshore waters, and coastlines.
Rays primarily feed on molluscs, crustaceans, worms, and occasionally smaller fishes. Some rays crush their prey between their blunt teeth, sometimes referred to as bony plates. Often completely burying themselves in the sand or soft sediment, rays are camouflaged by a grayish-brown, often mottled coloration.
Reminiscent of birds in flight, some rays gently flap their enlarged pectoral fins, or "wings," to "fly" through and sometimes even leap out of the water. A ray’s wingspan, or disc-size, can range from about 30 cm (12 in.) in yellow stingrays to over 6.1 m (20 ft.) in manta rays.Among the best know rays are stingrays, which have long, slim, whiplike tails armed with serrated, venomous spines. A stingray lashes its tail only as a defensive measure when it is caught, stepped on, or otherwise disturbed. When wading in shallow waters, people should shuffle their feet to avoid stepping on a buried stingray. In many parts of the world, some rays are commercially important food sources, yet currently, rays are not considered threatened or endangered. Due to humankind’s impact on the marine environment, however, concern is mounting for the future of rays throughout their range.
Food habits
All sharks are carnivorous and, with a few exceptions, have broad feeding preferences, governed largely by the size and availability of the prey. The recorded food of the (Galeocerdo cuvieri), for example, includes a wide variety of fishes (including other sharks, skates, and stingrays), sea turtles, birds, sea lions, crustaceans, squid, and even carrion such as dead dogs and garbage thrown from ships. Sleeper sharks (Somniosus), which occur mainly in polar and subpolar regions, are known to feed on fishes, small whales, squid, crabs, seals, and carrion from whaling stations. Many bottom-dwelling sharks, such as the smooth dogfishes (Triakis and Mustelus), take crabs, lobsters, and other crustaceans, as well as small fishes.
The two giant sharks, the whale shark (Rhincodon typus) and basking shark (Cetorhinus maximus), resemble the baleen whales in feeding mode as well as in size. They feed exclusively or chiefly on minute passively drifting organisms (plankton). To remove these from the water and concentrate them, each of these species is equipped with a special straining apparatus analogous to baleen in whales. The basking shark has modified gill rakers, the whale shark elaborate spongy tissue supported by the gill arches. The whale shark also eats small, schooling fishes.
The (Pristiophoridae) and (Pristidae) share a specialized mode of feeding that depends on the use of the long, bladelike snout, or "saw." Equipped with sharp teeth on its sides, the saw is slashed from side to side, impaling, stunning, or cutting the prey fish. Saw sharks live in midwaters; sawfishes, like most other rays, are bottom inhabitants.
(Alopias) feed on open-water schooling fishes, such as mackerel, herring, and bonito, and on squid. The long upper lobe of the tail, which may be half the total length of the shark, is used to frighten the fish (sometimes by flailing the water surface) into a concentrated mass convenient for slaughter.
Most sharks and probably most rays segregate according to size, a habit that protects smaller individuals from predation by larger ones. Even among sharks of a size category, dominance between species is apparent in feeding competition, suggesting a definite nipping order. Other sharks keep clear of (Sphyrna), whose manoeuvrability, enhanced by the rudder effect of the head, gives them an advantage. When potential prey is discovered, sharks circle it, appearing seemingly out of nowhere and frequently approaching from below. Feeding behaviour is stimulated by numbers and rapid swimming, when three or more sharks appear in the presence of food. Activity soon progresses from tight circling to rapid crisscross passes. Biting habits vary with feeding methods and dentition. Sharks with teeth adapted for shearing and sawing are aided in biting by body motions that include rotation of the whole body, twisting movements of the head, and rapid vibrations of the head. As the shark comes into position, the jaws are protruded, erecting and locking the teeth into position. The bite is extremely powerful; a (Isurus), when attacking a swordfish too large to be swallowed whole, may remove the prey's tail with one bite. Under strong feeding stimuli, the sharks' excitement may intensify into what is termed a feeding frenzy, in which not only the prey but also injured members of the feeding pack are devoured, regardless of size.
In most cases the initial attraction to the food is by smell. Laboratory studies have shown that sharks do not experience hunger in the normal sense of the word, and they are much more prone to be stimulated to feeding by the olfactory or visual cues announcing the appearance of prey.
Manta, or devil, rays swim mostly at or near the surface, progressing by flapping motions of the pectoral fins. Even the largest often leap clear of the water. In feeding, a manta moves through masses of macroplankton or schools of small fish, turning slowly from side to side and using the prominent cephalic fins, which project forward on each side of the mouth, to fan the prey into the broad mouth.
Chimaeras and ghost sharks dwell near the bottom in coastal and deep waters, to depths of at least 2,500 metres (about 8,000 feet). They are active at night, feeding almost exclusively on small invertebrates and fishe
Reproductive behavior
Mature individuals of some species of sharks segregate by sex, coming together only during the mating season, when the males, at least those of the larger, more aggressive species, stop feeding. Segregation is a behavioral adaptation to protect the females, one principal courting activity used by the male to induce cooperation of the female in mating being that of slashing her with teeth especially developed for that purpose. After mating, the sexes again separate. The pregnant females also tend to keep apart from the other females of like size. As the time of parturition approaches, the pregnant females move to particular areas, which presumably have properties of environment especially suitable as nursery grounds. When giving birth to their young, they stop feeding, and, soon after parturition is completed, they depart.
Nursery areas vary with species. Some sharks--e.g., the bull and sandbar sharks--use shallow waters of bays and estuaries; the silky shark uses the bottom far out on oceanic banks such as the Serrana Bank in the western Caribbean. The Atlantic (Squalus acanthias) bears its young mostly during the winter far out on the continental shelf of northeastern America almost two years after mating.
A few skates that have been observed mating may be characteristic of other rays. The male seizes the female by biting the pectoral fin and presses his ventral surface against hers while inserting one, or in some species, both claspers into her cloaca. Male skates have one to five rows of clawlike spines on the dorsal side of each pectoral fin. These are retractile in grooves of the skin and are used to hold the female during mating.
The eggs of skates in aquaria have been observed to be extruded in series, usually of two but sometimes one, with rests of one to five days between extrusions. A female of a European skate, Raja brachyura, laid 25 eggs over a 49-day period in the aquarium located at Plymouth, England.
Although the mating of chimaeroids has not been observed, it is generally presumed that the mode of copulation is similar to that of sharks and that the male's frontal spine and anterior appendage of the pelvic fins are probably used in securing the female. Two eggs are laid simultaneously, one from each oviduct. They are often carried for a relatively long period before being laid, several hours or even days, each protruding for the greater part of its length.
All species of sharks, rays, and chimaeras produce large, yolk-rich . These are fertilized internally, for which the males are equipped with two copulatory organs called claspers along the inner edges of the pelvic fins. Each clasper has a groove for guidance of sperm. The few published descriptions of mating sharks and rays are probably characteristic of the entire group. The male grasps one of the female's pectoral fins with his teeth to hold her in position as he inserts a clasper through a cavity (cloaca) and into a tube (oviduct). Males of most species probably use only one clasper at a time. The sperm travel to the anterior end of the oviduct, where they fertilize the eggs. The eggs then move down the oviduct past the shell gland, where they are covered by a shell or capsule.
In oviparous (egg-laying) species, which include some of the sharks, probably all the skates, possibly some of the guitarfishes, and all of the chimaeras, the eggs are enveloped in a horny shell, usually equipped with tendrils for coiling around solid objects or with spikelike projections for anchoring in mud or sand. The egg cases of most species are more or less pillow-shaped; those of the (Heterodontidae) are screw-shaped with a spiral flange. The eggs of chimaeras are elliptic, spindle-shaped, or tadpole-shaped and open to the exterior through pores and slits that permit entrance of water during incubation. An egg of the found in the Gulf of Mexico measured 30 centimetres (12 inches) long by about 14 centimetres (51/2 inches) wide and was eight centimetres (three inches) thick. Protected by the shell and nourished by the abundant yolk, the embryo of an oviparous species develops for 41/2 to 143/4 months before hatching.
The majority of sharks and most, possibly all, rays other than the skates are ovoviviparous (i.e., the egg hatches within the mother). In this case, the egg is first coated in the shell gland with a temporary membranous capsule that lasts only during early development. After emerging from its capsule, the embryo remains in the oviduct of the mother, nourished by the yolk sac to which it remains attached. Embryos of some ovoviviparous sharks, notably the porbeagle (Lamna nasus), mako (Isurus oxyrinchus), and (Odontaspis taurus), ingest yolks of other eggs and even other embryos within the oviduct of the mother after the contents of their own yolk sacs are exhausted. In the majority of ovoviviparous sharks and rays, organically rich uterine secretions provide supplemental nourishment, which is absorbed by the yolk sac and in many cases by appendages borne on its stalk. In some genera of rays, vascular filaments producing these secretions extend through the spiracles and into the digestive tract of the embryos.
Several shark species are viviparous--i.e., the yolk sac develops folds and projections that interdigitate with corresponding folds of the uterine wall, thus forming a yolk placenta through which nutrient material is passed from the mother.
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