Spotted Eagle Ray
Rays and skates are a cartilaginous fish like sharks. Unlike sharks who have to constantly thrash their tails to maintain their position in mid-water, most rays and skates spend their time at the bottom of the sea. They are found throughout the world with rays being most diverse in the tropic and skates being more widespread in temperate waters. Most species live in coastal waters. Some live in freshwater and few can live in both salt and fresh water. A species of freshwater ray living in Southeast Asia may be the world’s largest freshwater fish.

Rays and skates have broad, flat bodies and winglike fins. Through evolution their pectoral fins enlarged into undulating lateral triangles that allow them to move. Their tail has lost nearly all of its muscles and has become thin and whiplike. Rays have a barbed spine on their tails that is coated with toxic compounds. The shape of the their bodies is adapted for siting on the sea bottom although some species like eagle rays and manta rays swim in the open sea.

All rays and skates are carnivorous. They live primarily on mollusks and crustaceans they suck up from the ocean floor and crush with their mouths which are located on the undersides of their bodies. Their teeth are designed to grasp, rasp and crush food rather than tear it apart. Many are camouflaged the same color as the sea bottom. This is more of an adaption to escape predators rather than catch prey. A few species like the manta are filter feeders.

BBQ stingray
Ray and skate wings are pectoral fins used in propulsion. Large species flap them like wings. Like sharks they have an oil filled liver used to maintain buoyancy but is smaller than that of sharks, allowing them to settle on the sea floor. Many species of ray and skate either lack scales or have large thornlike scales. Most skates reproduce by releasing large, leathery egg capsules with one or more developing offspring inside. Many rays produce eggs that hatch inside the female’s body and live off yolk before being released. The eggs and young of some species are given further nourishment by fluid delivered from a membrane inside the mother.

Many ray and skate species partially bury themselves in sediments. The location of the mouth on the underside of the body presents a problem when it comes to breathing. If they were to breath through their mouths like sharks they would take in large amounts of mud and sand. Instead, they breath by taking in water through two openings called spiracles on the surface of their head, behind the eyes that bypass the mouth and lead straight to the gills, where oxygen is extracted and water is expelled in the underside of the body through the gill slits.

Rays and skates are good diggers. They are sort of like pigs of the sea, rooting out sea creatures such as clams and worms that bury themselves in sea sediments. The often tear up sea grass bed in search of food.

Lesser electric ray
Websites and Resources: National Oceanic and Atmospheric Administration ; Smithsonian Oceans Portal ; Ocean World ; Woods Hole Oceanographic Institute ; Cousteau Society ; Montery Bay Aquarium

Websites and Resources on Fish and Marine Life: MarineBio ; Census of Marine Life ; Marine Life Images ; Marine Species Gallery

Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) ; International Coral Reef Initiative ; Wikipedia article Wikipedia ; Coral Reef Alliance ; Global Coral reef Alliance ; Coral Reef Pictures ; The Global Coral Reef Monitoring Network; the International Coral Reef Action Network.

Cartilaginous Fishes

Stingray in Goa
Sharks, rays and a group of deep-water fish called chimaeras and their relatives are cartilaginous fish, or elasmobranch, as opposed to bony fish, the classification most fish fall into. All cartilaginous fish possess skeletons made of cartilage rather than bone and specialized teeth that can be replaced throughout their lives. Some have cartilage strengthened by mineral deposits and bonelike dorsal spines.

Cartilaginous skeletons are much lighter and more flexible than bony skeletons. On the land they would be unable to support the weight of large animals but in water they are effective for animals up to 40 feet in length. Most have skin covered by thousands, even millions, of interlocking scales called dermal denticles. They have a similar composition to teeth and give skin a sandpaper-like texture, increase durability and reduce drag.

Cartilaginous fish have five to seven pairs of gills. When water enters the mouth the gill slits are closed. When waters passes through the open gills the mouth is closed. These fish also lack the air bladder that give bony fish their buoyancy and instead have an oil-rich liver that adds to their buoyancy. Even so many are negatively buoyant and need to swim to stay afloat.

All cartilaginous fish have a sensory system of pores called ampullae of Lorenzini, named after an Italian biologist who discovered them in 1678, that send out electrical signals that can be used to locate prey and avoid predators. Most also have an effective lateral line system running from their tail to their snout that helps them detect small vibrations.

All cartilaginous fish are carnivorous but for some this means they feed primarily on zooplankton. Most feed on live prey but will feed on carrion if it is available. Few feed exclusively on carrion. Reproduction take place internally when the male passes sperm into the female’s cloaca with a modified pelvic fin. Some species release embryos in leathery egg cases. Other species give birth to live young that hatched from eggs that broke open inside the female. In yet others, embryos develop in placenta-like structures. In all cases the young do not go through a larval stage like many bony fish; instead they are born as miniature adults.

Electric Rays and Other Species of Ray and Skate

20120518-ray_parking_bay o_de_Lisboa.jpg The marbled electric ray is a species that reaches lengths of 60 centimeters and weights of 13 kilograms and is found in the eastern Atlantic and Mediterranean. While many species of shark and ray produce electricity to detect prey this species generates enough electricity to produce a powerful jolt of 30 to 40 volts that can stun or outright kill prey. Although such shocks are not fatal to humans they can be quite unpleasant. These rays are most active during the day and evening. They spend the bulk of their time lying on the ocean bed waiting for prey to pass its way.

Eagle rays are large rays that reach a length of 2.5 meters and a weight of 30 kilograms and are found in the eastern Atlantic, Mediterranean and southwest Indian Ocean. They have wide, narrow pectoral fins and an exceptionally long tail with a poisonous spine. These rays are equally at home in the open ocean and on the ocean floors, using their seven rows of flat teeth to crush prey, which it exposes in the sediment by flapping its fins and blowing jets of water. Eagle rays are strong swimmers and can leap completely out of the water. Spotted eagle rays glide around reefs and sand flats and feed mainly on mollusks in the sand.

Cownose rays sometimes gather in huge schools with hundreds or thousands of individuals and move like a large flock of birds with slowly beating wing. With a wing span up to a meter across, they tend to stay close to the shoreline and congregate in coastal bays, where they pursue shell fish that they suck from the sand and crush with their tooth plates. These rays have increased in numbers in some places as their natural predators — name large sharks — have been overfishing. Cownose rays gobble up clams, scallops and oysters and can cause serious damage to local shellfish industries.

Ratfish are a kind of ray. They are found mostly in deep inshore waters and have disproportionally large heads and a downward facing mouth.


Southern stingrays at stingray city
Stingrays sting, not with the end of their tails, but with a spine sticking out of the middle of the tail that pops out like a switchblade when the ray feels threatened. Human victims, who accidently step on a stingray or kick it, receive an excruciatingly painful and severe but rarely lethal sting on the ankle.╛

Stingrays lay motionless at the bottom of the sea or in shallow water most of the time. Since v1 they usually can not see their prey — their eyes are on the top of their head and their mouth and usually their food is at the bottom — they use highly developed electro-receptors to touch, smell and locate food. Once a mollusk, worm or crustacean has been found the ray drapes itself over the prey, and suck it in like a vacuum cleaner.╛

Stingrays will whip up their tails in defense. The tail can cause a nasty, painful, ragged wound but even more worrisome sometimes are the venemous spines which run along the stingrays back. When moving about in a place with stingrays one should make their presence known by making noise and moving around and give the ray enough warning to flee.

Stingray injury
Many more people are hospitalized every year for injuries from stingrays than shark bites. People who have been stung say it is the most painful thing they have ever experienced. The sting can also cause rapid onset of nausea, vomiting, and breathing difficulties. Wounded area may become ulcerous and even gangrenous.

The blue-spotted stingray is a colorful, often-photographed species found in the Indo-Pacific region. Reaching a length of two meters and a weight of 30 kilograms, it possesses blue spots scattered over a greenish or yellowish body and has blue strips running along the sides of its tail. It is often found in sandy areas next to reefs and rests in cave or crevices, These rays both forage for food and lie in wait in the sand for prey to come their way. The tail contains a powerful toxin that can result in a nasty sting if the ray is mishandled or stepped on.

Overpopulation of Rays

In January 2011, National Geographic reported, “With a three-foot wingspan, an adult Rhinoptera bonasus can weigh 40 pounds. Also known as cownose rays, they have take over the Chesapeake Bay each summer, taxing an already fragile ecosystem by gobbling shellfish and roiling grass beds. Shaped like kites, they taste like tuna. Now area officials see a potential win-win: Whet human appetites with a tasteful name (“Chesapeake ray”) and rebalance the bay. [Source: Jeremy Berlin, National Geographic, January 5,2011]

Rays aren’t invasive newcomers here; in 1608 one stung explorer John Smith. But as predators like coastal sharks have declined, the observed spike in cownoses, though untallied, could be grounds for a carefully monitored fishery — and new revenue streams for watermen, retailers, and localities.

Attacks by Eagle Rays and Stingrays

eagle ray
In March 2008, a 55-year-old woman was killed near Marathon Key, Florida when an eagle ray — with a meter and half wing span and weighing 36 kilograms — leapt out the water and struck her while she was boating with her family. The woman was pronounce dead at a local hospital. Initially it was said she was struck the neck by the ray’s it barbed tail but no evidence of any puncture was found. Rather she died from injuries sustained by the impact with the ray and the boat after she fell down. The boat was traveling at 40 kph. Rays sometimes leap out of the water but it is was freak accident for one to hit a person like this.

In 2006, Steve Irwin, the star of the popular television show “Crocodile Hunter” was killed by a stingray while doing a shoot in diving gear at the Great Barrier reef in eastern Australia. Forty-four-year-old Irwin was swimming with the ray and handling it when it suddenly sent a serrated poisonous spine into Irwin’s heart. Irwin pulled the spine from his chest but then immediately fell unconscious. This much was video taped. After that the cameraman turned off his camera. There was some debate for a while as to whether the video would ever be shown. You can see its now on YouTube.

Irwin died not because he simply received a sting from the ray because the ray’s barb punctured his heart, another freaky occurrence. John Stainton, the manager and producer of the show that was being taped, told reporters that the tape “shows that Steve came over top of the ray and the tail came up, and spiked him here [in the chest], and he pulled it out and the next minute he’s gone. That was it. The cameraman had to shut down.”

Manta Rays

manta ray
Once referred to as devil fish and first described in 1798, manta rays are docile, plankton-eating fish with a wing span of up to 20 feet and can weigh 1 ¾ tons. The world’s largest rays, they are found in tropical and sometimes warm temperate waters. Little is known about their breeding habits and life span. Scientist aren't even sure how many species there are. [Source: David Doubilet, National Geographic, December, 1995]

Bruce Barcott wrote in National Geographic, “Generations ago those hornlike cephalic fins earned mantas the name devilfish. Their terrifying size and bat shape fed an aura of mystery and menace, and mantas were vilified as ferocious monsters. That changed in the 1970s, when scuba divers found mantas to be gentle creatures. Sometimes they even permitted humans to catch joyrides on their broad backs. [Source: Bruce Barcott, National Geographic, July 2009]

Scientific knowledge about mantas remains surprisingly thin. Only last year a leading expert proposed splitting the species in two: smaller resident mantas...that remain near shore, and larger transient mantas (with wingspans as great as 22 feet) that roam the world's tropical and semitropical oceans. And researchers are just beginning to learn more about those cephalic fins. "When you approach a manta, it will unroll a cephalic fin and wave it back and forth as if it's scanning," says Robert Rubin, a California-based marine biologist who's studied mantas in Mexico for 20 years. "Mantas are essentially flat sharks, and we know some sharks have electrical receptors in their faces. The hypothesis is that mantas use those fins to pick up electrical signals from other animals moving in the water."

Manta Ray Characteristics

Manta ray in Thailand
Manta rays are classified in ten species, with the giant manta ray being the largest species. They are generally solitary creatures who sometimes swim in small, loosely-organized schools. Small manta ray sometimes swim together in formations that from the air resemble squadrons of stealth bombers. Mantas have few natural predators except perhaps large sharks and killer whales. Occasionally mantas are spotted with shark bite marks.

Unlike most other rays and skates, which tend to spend their time on the sea floor and undulate their bodies to get around, manta rays swim in the ocean like marine versions of flying dinosaurs. They use their large wing-like pectoral fins to slap and glide through the water much same way a bird flies through the sky. They normally swims at a slow, easy-gong pace, beating their pectoral fins up and down about 10 times a minute, but are capable of accelerating quickly to avoid predators and can leap out of the water, somersault in the air and hit the surface with a loud crash. When they feed on plankton sometimes they rise through the water in spiraling motion, with their mouth agape, then descend and repeat the motion.

Manta rays emit an electric field and have only a short tail with no fins or poisonous barb. During the mating season males chase females and swim underneath them so their undersides face each. If a pair decides to mate the male inserts his claspers. The female give birth to one or two young a year, each about 1.2 meters wide.

Manta rays are regularly seen off Yap, a north Pacific island in Micronesia; off the Kona Coast of Hawaii; and near San Benedicto, one of the Revillagigedo Islands, 250 miles south of Mexico's Baja, California. Yap is one of the few places in the world where manta rays are encountered on nearly a daily basis. In the winter the manta rays come to Manta Ridge in Mili Channel for cleaning. Diver usually hold on to a ledge 30 feet below the surface and watch them cruise by. It is not unusual for divers to see six or seven manta rays at one time. In Hawaii, boats sometimes use light to attract clouds of plankton, which in turn attract manta rays.

Feeding Manta Rays

Manta feeding
Unlike most rays which have their mouths on the underside of their bodies, the manta ray has its mouth at the front of its body, allowing it to feed continuously as it moves through the sea.

Manta rays are attracted by masses of plankton. When feeding, manta rays open their mouths wide and use their "horns" (cephalic fins) to direct food and water into their mouths. The water leaves through the manta ray’s throat through slits on either side of its head. The slits are lined with combs that catch plankton. Manta ray gills are flared to allow large volumes of water to pass through their mouth and filtering system.

Manta rays also eat small schooling fish. They are often hang out on the edges of reef channels where the changing tide carry eggs, larval fish and tiny crustaceans out to the open sea. They often follow the tides and feed virtually non-stop.

Manta Ray Hitchhikers and Cleaning Stations

manta ray in Okinawa
In a phenomena only discovered in 1988, normally-open-ocean manta rays were observed coming to special "cleaning stations," specific rocks or areas along channels off the island of Yap in Micronesia, where small fish called wrasses removed parasites from their bodies while the manta rays fluttered in place in the current. The grooming of algae and other marine growths by wrasses is believed to help manta rays fend off life-threatening infections.

Describing the wrasses at work, David Doubilet wrote in National Geographic, "Suddenly wrasses about three inches long dart from the coral below and head for the manta. The creature then opens its enormous mouth, and a wrasse enters the white cave, picking between the gill arches that support the gills.”

Other fish such as orange clarion angelfish have also been observed cleaning parasites and marine growth off of manta rays. Jacks have been seen nipping at loose manta skin and using the bodies of mantas as covers for raids on other fish. Manta rays are often accompanied by fusilier fish. Remora often attach themselves to the manta ray body.

When approached by a diver, manta rays sometimes turn over their back so their stomachs can be scratched. On occasion groups of mantas have been observed leaping clear out of the water. When they hit the water the make a resonating slapping sound that can sometimes be heard more than a mile away. Scientist speculate that the manta rays do this to try to dislodge parasites. They probably like be scratched for the same reason.

Manta Ray Hunts, Pearl Divers and Shark Fin Soup

Manta ray in Yap
Whalers from the village of Lamalera on Lembata, a harsh volcanic island near Flores in Indonesia hunt manta rays by jumping on their backs. Describing this Jeffrey Gettleman wrote in Los Angeles Times, "The fishermen stroked across the water, scanning for signs of life. After hours of searching, one sinewy fisherman, Francise Bole Beding, saw a black fin pop through the surface...Paddlers yanked in their oars. Mr. Beding, a harpooner, scampered to the bow, a crude spear in his hands. He coiled himself, preparing to leap down onto the prey and drive harpoon deep into its flesh.”

"The sight of a fin cutting through the water focused all minds on what swam below. Mr. Beding saw it was a manta ray, not a whale, and because the giant rays are swift swimmers, he had to attack quickly... Mr. Beding leaped. The rope tied to the end of his harpoon spooled out furiously. The boat careened to the side as the three-meter-wide manta tried to bolt, a harpoon driven deep into its back. Mr. Beding fought the fish in a cloud of red water until two men plunged overboard with heavy iron hooks to finish it off...The paddlers dragged the limp, 136-kilogram fish up on the deck. Mr Beding and the other men wriggled back into the boat."

Pearl diver Yashinori Maeda was almost killed by a manta ray that became entangled in his diving gear. He told National Geographic, "I was collecting oysters 70 feet down when a giant manta snagged my air hose and safety line. Then it must have panicked. It was so strong that it pulled my helmet off the breastplate, breaking the screw threads...Wearing lead shoes and a lead belt, I could not swim to the surface. I was drowning when my tender saw I was in trouble and pulled me up."

A shortage of shark fins has led suppliers to look for other sources to meet demand. Among the sources they are turning to are the wings of manta rays. They are targeted because the swim near the surface and are easy to catch and their wings are big. Most the fins end up in a poor man’s shark fin soup made ray cartilage and low grade shark fins.

Manta Rays Feast Around a Small island in the Maldives

Manta in the Maldives
Bruce Barcott wrote in National Geographic, In the Maldives, “there is an uninhabited island named Hanifaru. It's not much to see from the air: a spray of tropical shrubs on what appears to be a truckload of sand. Hanifaru is so small a child could walk its entire scimitar-shaped coastline in a ten-minute stroll. The island's size isn't unusual for the Maldives, a collection of 1,192 tiny islands clumped in 26 atolls encompassed by the vastness of the Indian Ocean. But several times a year, when time and tide align, manta rays from throughout the Maldives converge here to feed in a spectacular coral-reef ballet.” [Source: Bruce Barcott, National Geographic, July 2009]

From May through November, when the lunar tide pushes against the Indian Ocean's southwestern monsoon current, a suction effect pulls tropical krill and other plankton from deep water up to the surface. The current sweeps the krill into the cul-de-sac of Hanifaru Bay. If the krill stayed at the surface, they'd wash over the bay's coral walls and out to the safety of the open sea. But they can't. Instinct forces them to dive away from daylight. When they do, they get trapped deep in the bowl. In just a few hours a massive concentration of plankton builds up, a swarm so thick it turns the water cloudy.

Cue Manta birostris. "Just after high tide you'll see a few manta rays turn up," says Guy Stevens, a British marine biologist who's been researching the Maldives mantas for the past three years. "Then poof, a whole group will move in, and you'll get as many as 200 feeding for two to four hours in a bay no bigger than a soccer field." These massive fish (the wingspans of Maldives mantas can reach 12 feet) are dynamic filter feeders, shoveling their shoe-box mouths through krill like threshers through wheat, inhaling prey. They barrel roll when they hit a rich patch, somersaulting backward to stay in the hot spot. They chain feed, following each other in a train of open maws.

In the tight confines of Hanifaru Bay, mantas must expand their repertoire, and Stevens has identified maneuvers rarely seen by scientists. When 50 or more fish chain feed in the bay, something extraordinary happens. The head of the line catches the tail, and the chain spins into a vortex. "We call that cyclone feeding," says Stevens. "When you get more than a hundred mantas doing that, they start to spiral out. When the chain breaks down, you get chaos feeding." The stately dance in the milky waters turns into a free-for-all, with hundreds of mantas bumping into each other. Adding to the confusion are whale sharks — languid, plankton-eating giants, each about the size of a 40-foot shipping container — that show up to share the spoils. Within hours the plankton run out, the feast winds down, and the mantas plow the bay's sandy bottom with their cephalic fins to throw hidden prey back into the water column.

Manta Rays as Tourist Attractions

Because of their accommodating nature, mantas today have achieved the dubious status of dive-tourism attractions, luring humans to swim with them in closer-than-optimum quarters. For a species considered near threatened, however, this newfound popularity could literally be a lifesaver. Mantas, with their slow reproductive rate, are vulnerable to overfishing, so a robust tourist trade could give local communities an economic incentive to conserve the fish rather than kill them. It's a delicate balance, though — too many humans could drive mantas out of feeding grounds like Hanifaru Bay.

To avoid that, Stevens has proposed turning the bay into a marine sanctuary. A new Maldives president has vowed to strengthen the archipelago's marine protections, but his government has so far been slow to respond to Stevens's idea. "I'm not ruling out declaring Hanifaru a marine-life sanctuary. But we need to increase our ability to enforce existing environmental laws before creating new protected areas," says Environment Minister Mohamed Aslam.

In the Maldives, Stevens continues to catalog the local animals. (He's identified more than 1,500 individuals by their unique spot patterns.) His data also record the exact timing of the feedings, information that would be of great value to the local guide industry. Stevens hears the clock ticking, and he is scrambling to organize a self-policing regime among resorts and local guides before dive tourists overrun Hanifaru. "We don't want to ruin what we've got here," he says. If his plan works, Hanifaru Bay will remain a sanctuary for cyclone-feeding manta rays, with just enough room for whale sharks, and humans as well.

Sawfish and Guitarfish

Sawfish are members of the shark and ray family. The have a long saw-like snout and body that looks like that of a cross between a ray and a shark. They sometimes reach 20 feet in length (including a six-foot snout) and weigh up to 700 pounds. Sawfish are fairly common in the Gulf of Mexico. In other places they endangers species and have been overfished and their saws have been harvested as souvenirs.

The "saw" is flat extension of the snout, covered with tough skin called “shagree”. It has two edges with about 25 pairs of long, sharp teeth. The snout can reach a length of six feet and a foot wide at the base. The saw is used primarily to dig up food in sand and mud. Sawfish are generally not aggressive and are dangerous only of mishandled or harassed by divers.

The smalltooth sawfish is found in the Indo-pacific region and the eastern and western Atlantic. It has 24 to 32 pairs of pointed teeth on either use of its snout, which makes up 30 percent of its body length. It has a flattened head, small eyes and mouth and gills on the undersides of the head, It feeds by patrolling along the sea bed and suck up small organisms it encounters; sashes at schools of fish with it saw and feed on injured fish. It is found mostly in shallow water around beaches and bays but is occasionally in the mouths of river and freshwater streams.

The guitarfish is another member of the ray and skate family. The shovelnose guitarfish is a species found in the eastern Pacific that reaches a length of 1.5 meters and a weight of 18 kilograms. It has a broad head and clear, cartilaginous areas on either side its snout, wide ray-like pectoral fins, and a body that is otherwise like that of a shark. It is often found in shallow water in and around beaches, bays and estuaries where it lies partially buried in the sand or mud and feeds on small bottom-dwelling fishing, crustaceans or worms that it uncovers.

Image Source: National Oceanic and Atmospheric Administration (NOAA) except second manta Okinawa Convention and Vistors Bureau

Text Sources: Mostly National Geographic articles. Also the New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2011

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