REEF AND COASTAL SHARKS
Bamboo Shark The presence of sharks in a reef is a sign of a healthy ecosystem. As top predators they help keep other carnivores from becoming too numerous and depleting herbivorous species. They also weed out sick and weak fish, leaving the fittest tor survive. This helps keep the reef diverse and vibrant.
Zebra sharks are most commonly found inc coral reefs. Reaching lengths of 3.5 meters but weighing only around 30 kilograms, these slender sharks have very flexible bodies and a unique downward pointing mouth near the end of its snout that allows it to penetrate deep in reef crevices to snag crabs, shrimps and small bony fish and scoop up mollusks on the ocean floor. During down time. It rests on the ocean floor, propped on it pectoral fins, facing the current.
The leopard shark has distinctive black spots on its sides and fins. Similar to about six other species and found in the eastern Pacific it reaches lengths of about 2.1 meters and weighs around 32 kilograms and uses its relatively small, sharp teeth grab a wide variety of prey, including burrowing invertebrates whose exposed parts the shark quickly snags.
Bronze whalers are a dangerous and common shark found mostly off Australia and South Africa. They have been involved in a number of attacks.
Horn shark Websites and Resources: National Oceanic and Atmospheric Administration noaa.gov/ocean ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Ocean World oceanworld.tamu.edu ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Montery Bay Aquarium montereybayaquarium.org
Websites and Resources on Fish and Marine Life: MarineBio marinebio.org/oceans/creatures ; Census of Marine Life coml.org/image-gallery ; Marine Life Images marinelifeimages.com/photostore/index ; Marine Species Gallery scuba-equipment-usa.com/marine
Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) coris.noaa.gov ; International Coral Reef Initiative icriforum.org ; Wikipedia article Wikipedia ; Coral Reef Alliance coral.org ; Global Coral reef Alliance globalcoral.org ; Coral Reef Pictures squidoo.com/coral-reef-pictures ; The Global Coral Reef Monitoring Network; the International Coral Reef Action Network.
Blacktip Reef Sharks
blacktip reef shark Blacktip reef sharks are the most commonly encountered shark in tropical waters the Pacific and Indian Oceans. They are found around reefs and in shallow waters. Their dorsal and tail fins often project above the water and have black tips, hence its name.
Blacktip reef sharks reach lengths of two meters and weights of about 45 kilograms. They give birth to live young. They have streamlined bodies and are excellent and powerful swimmers. Blacktip sharks are "gregarious creatures that travel in large groups and somersaults out of the water during feeding frenzies."
Studies of black tips indicates they the head to warmer waters in the winter but return to their nursery ground when the weather warms. Research indicates the sharks have a very sophisticated navigation system that allows them to migrate to certain points in the ocean at specific times.
Blacktip reef sharks are regarded as inquisitive but not dangerous. They occasionally bite divers, surfers and waders, seemingly accidently, as they chase schools of bait fish near the shore but are generally not aggressive. Between 1876 and 2001, they were involved in 14 recorded unprovoked attacks.
Grey Reef Sharks
Gray reef shark range across the Indian ocean, and the islands and atolls of Indonesia, the Philippines and the South Pacific. Attaining a length of six feet or more, these medium-size sharks prowl the reefs with "slow flicks of it black-edged tail." [Source: Bill Curtsinger, National Geographic January 1995]
Gray reef sharks can be very aggressive. When an intruder such as a diver enters their territory, they often adopt an aggressive posture with their back arched, the pectoral fins lowers and snout raised, swimming from side to side in a "threat posture analogous to a rattlesnake.”
Attacks By a Grey Reef Shark
Carribbean reef shark Describing an attack by a gray reef shark, Curtsinger wrote: the shark "tore open my left hand, I remember feeling as if I'd been hit by a sledge hammer. Such was the shock, I don't recall the actual bite." The incident took place in 1973 in waters off a South Pacific atoll. "It was 20 feet away and closing. I saw it sweeping its head back and forth; its back was arched like a cat's. The shark was speaking to me, but at the time I didn't know the words."
"The shark came at me like a rocket. I had time only to lift my hand, the shark ripping it with its teeth. As I swam frantically toward the boat, I saw that each dip of my hand left a cloud of blood in the water. the shark struck again, raking my right shoulder. At that moment a friend in a dingy rescued me." Now Curtsinger sometimes wears a steel mesh diving suit or a protective plastic "shark scooter."
Describing another attack by a gray reef shark that he believed was injured, photographer Mike deGruy said, "I raised my camera and took a picture and it ripped up my right arm and then my left scuba fin. Luckily, it grabbed my fin and not my thigh. I came to the surface spewing blood everyplace. I swam with my left leg back to the boat."
"Three quarters of the way to the boat, I felt I might make it." Suddenly he wondered: "Why am I not being eaten? Then, it was like an epithet. 'Phil!' They're eating Phil!" His diving partner Phil was seriously injured. DeGruy required 11 operations over a year and a half to repair the damage that was done to him.
leopard shark Lemon sharks are found mostly in tropical waters the eastern Pacific and the western and eastern Atlantic Oceans. They are found around reefs and in shallow waters and can survive in brackish water in areas with low oxygen and feeds mainly on bony fishes, guitarfish and stingrays and may also eat crustaceans, mollusks and seabirds.
Lemon sharks are one of the most studied sharks because they adapts better to captivity than other sharks and they are found in waters off the United States and the Bahamas where scientists are studying sharks. Lemon sharks have a powerful bite and may attack humans if provoked. In 1993 in Monroe County was off Key West a snorkeler was bit by a lemon shark.
Also known as sharptooth sharks, lemon sharks reach a lengths of 3.4 meter and a weight of 185 kilograms. They are yellowish or light brown in color and have large fins and an abrupt snout. Lemon sharks take 12 to 15 years to reach maturity, at which time they may weigh 100 kilograms and be 2.8 meters in length. Adults are most active at night. Juveniles are most active in the day.
Lemon sharks give birth to live young and breed in shallows and young sharks spend their first year around mangrove swamps, feeding on small fish and crustaceans and staying shallow waters were there are less vulnerable to attacks from larger fish, especially other sharks. In the Bahamas there are large numbers of youngsters living in mangrove swamps which offer them a plentiful supply of food and few dangers than in the open sea and around reefs.
Lemon sharks have the distinction of being the only known marine species that practices internal fertilization and polyandry. Each breeding season, the female mates with several males. And this in itself is significant because each sexual encounter often involves a lot of biting and blood.
Sharks have only been observed mating a handful of times. At first it was though they copulated stomach to stomach, but in 1959 a scientist watched a pair of lemon sharks mating side by side, moving in synch, as if they were a "single monster with two heads." Until recently most of what was known about shark reproduction was based on chance encounters at sea or reports by fishing guides.
Nurse shark Nurse sharks are one of the most benign and sluggish shark species. Reaching a length of 4.3 meters and a weight of 150 kilograms, they spend much of their time cruising the bottom of the sea near the shore and searching through rocky crevices and caves for prey such as squid, crabs and lobsters. Their name comes from the powerful sucking sound made by their powerful throat muscle, small mouth and large pharynx which in the old days reminded some people who heard it of nursing children.
Nurse sharks are found in shallow, inshore areas in western and eastern Atlantic and the eastern Pacific. They have very tough skin and a pair of barbels under their mouths that are used in sensing out the invertebrates that it feeds on. Like rays, they spend a lot of time just just lying on the sea bottom. They can “walk” along the bottom using their pectoral fins like limbs and sometimes are found in groups with several dozen individuals.
Nurse sharks create vacuums with mouth and suck prey from crevices. They can suck stubborn, hard-to-dislodge prey from the their hiding places into their mouths in a as little as 50 milliseconds. Nurse sharks give birth to live young and produce litters of 20 or 30 pups..
Mating Nurse Sharks
Nurse sharks Describing a pair of nurse shark mating off the Florida Keys, Harold L. Pratt Jr. and Jeffrey Carrier wrote in National Geographic, "To subdue his partner, the male must seize the females' pectoral fin, flip her, and carry her from the shallows to deeper water...Suddenly a spray of seawater erupts from the surface---it's the male shark lunging for a female's fin---and a tail slaps the water with a percussive boom." [Source: Harold L. Pratt Jr. and Jeffrey Carrier, National Geographic, May 1995]
"Amid a swirl of fins we watched as the male struggled to arch his body over the female... Often one of his penis-like claspers poked out of the water, pointing skyward." The male then got a tight grip on female's fin and aligns his body with hers. "Thus anchored he can roll the female over, flick his tail underneath her to brace himself, and insert the clasper. Successful copulation lasts between one and two minutes."
"Afterwards, the male collapsed on the sea bottom. This evident fatigue may result from the fact that the male is deprived of oxygen the whole time he has his jaws clamped onto the female's fin. After days of mating, the female swims away with a chewed up pectoral fin." Less than 10 percent of attempts to mate by nurse sharks end in success.
Nurse Shark Grab Boy and Wouldn’t Let Go
nurse shark Although they generally passive nurse sharks have bitten people who have harassed them. When provoked they will attack and hold on to the victim with unyielding pit-bull-like grip.
In 1998, year, a 16-year-old Illinois boy was bitten by a nurse shark off Marathon Key in the Florida Keys after he grabbed the shark's tail. The unrelenting shark wouldn't let go of the boy's chest, and stayed attached to the boy until he reached a hospital where doctors cut the animal's spine to kill it. [Source: Reuters]
The boy was scuba diving with his father near Marathon, when he saw a three-foot nurse shark swimming near him and grabbed its tail, emergency workers said. The shark bit his chest and wouldn’t let go.
The Florida Marine Patrol said nurse sharks swim slowly and can appear to be harmless, but they can be dangerous and should be avoided. "This is not unusual," said George Burgess, director of the International Shark Attack File. "It is hard to aggravate a nurse shark. They are pretty quiet animals, but if you get them mad, they hold on like a bulldog." "In one memorable incident, an off-duty police officer felt obliged to pull out his service revolver and shoot the shark off a victim on a beach in Fort Lauderdale or Miami," he said. Burgess doesn't count that incident in his statistics, he said, because it was a provoked attack. The child taunted the animal. He puts that one in a different file, he said: “S for Stupid.''
Sand Tiger Sharks
Dusky shark Sand tiger sharks are fearsome-looking creatures that swim around with their mouths open, exposing rows of spike-like teeth. In reality they are generally nonthreatening. They hoover in the water by swallowing surface air and holding in their stomachs to regulate its buoyancy. Their habit of swimming with their teeth exposed is actually a benign behavior called yawning.
Sand tiger sharks reach length of 4.4 meters and weigh up to 150 kilograms and are found in the eastern and western Atlantic, southern Indian and western Pacific Oceans. Their fearsome appearance but benign behavior makes them a favorite of aquariums around the world.
Sand tiger sharks have a large mouth and dorsal fins that are situated further back than on most sharks. They have light brown or beige and darker brown, somewhat tiger-like blotches scattered around its body, hence the name. They catch prey with a sneaky sideways snatch. A slow but strong swimmer, it feeds on a variety of bony fishes, squids, crabs and lobsters. Groups of them have been observed working to surround shoals of prey
Embryos are cannibalistic. The first to hatch eat the other eggs inside the egg case. Survivors grow teeth and eat other embryos in the uterus. Generally only one baby shark emerges alive from each of the shark’s two uteri.
Whitetip Reef Sharks
Whitetip reef sharks are found mostly in tropical waters the Pacific and Indian Oceans. They are found around reefs and in shallow waters and the open sea. Their dorsal and upper tail fins have distinctive white tips, hence their name.
Also known a bluntheads, Whitetip reef sharks reach a length of 2.1 meters and a weight of about 20 kilograms. They are slender and give birth to live young. Unlike most sharks which need to swim continuously to keep oxygen flowing through their gills, whitetip reef sharks can pump water across their gills and thus rest on the ocean floor.
Whitetip reef sharks are regarded as not dangerous. They are attracted by boat engines, presumably by an opportunity for a free meal, often show up when fish are speared and occasionally bite divers in such encounters but are generally not aggressive. In April 2001, a surfer was bitten on the left hand by a small white-tip reef shark in 10-foot waters off Ewa Beach in Hawaii White tips have been overfished. Many have been harvested for their fins.
Blacktip reef shark Image Source: National Oceanic and Atmospheric Administration (NOAA) noaa.gov/ocean ; Wikimedia Commons
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.
© 2009 Jeffrey Hays
Last updated March 2011