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|Bull shark - Carcharhinus leucas|
|Topic Started: Jan 9 2012, 01:35 PM (993 Views)|
|Taipan||Jan 9 2012, 01:35 PM Post #1|
Bull shark - Carcharhinus leucas
The bull shark, Carcharhinus leucas, also known as the bull whaler, Zambezi River shark or colloquially Zambi, is common worldwide in warm, shallow waters along coasts, and well-known for its unpredictable, often aggressive behaviour. They have a tolerance for fresh water that is unique among marine sharks, and can travel far up rivers, posing a threat to those who venture into the water. As a result they are probably responsible for the majority of attacks on humans that take place near the shore, including many attacks attributed to other species. They may be found far from the ocean but are not true freshwater sharks (unlike the river sharks of the genus Glyphis).
The name, "bull shark", comes from the shark's stocky shape, broad, flat snout and aggressive unpredictable behavior. In India, the bull shark is often called the Sundarbans or Ganges shark and is considered a delicacy for Bengali fish curries. In Africa it is also commonly called the Zambezi River shark or just Zambi. Its wide range and diverse habitats result in many other local names, for example Nicaragua shark, cub shark, shovelnose shark, freshwater whaler.
Distribution and habitat
The bull shark is common in the coastal areas of warm oceans, in rivers and lakes, and in both salt and fresh water. In the Atlantic it is found from Massachusetts to Southern Brazil and from Morocco to Angola. In the Indian Ocean it is found from South Africa to Kenya, India, Vietnam to Australia. It is estimated that there are more than 500 bull sharks in the Brisbane River and greater numbers still in the canals of the Gold Coast in Queensland, Australia. In the Pacific Ocean, it can be found from Baja California to Ecuador. The shark is found in the central Amazon River, and has been recorded as far up the Mississippi River as Illinois. It is also found in the fresh water Lake Nicaragua and the Ganges and Brahmaputra rivers of West Bengal and Assam in eastern India and adjoining Bangladesh. After Hurricane Katrina hit in 2005, a large number of bull sharks were sighted in Lake Ponchartrain. It is found to a depth of 150 m, but does not usually swim deeper than 30 m.
Anatomy and appearance
Bull sharks are large and stout. The males of this species can reach 2.1 metres (6.9 feet) and weigh 90 kilograms (198.4 lb). The females can be much larger: 3.5 m (11.5 ft) and 230 kg (507 lb). It is wider than other sharks of comparable length. It is grey on top and white below. The second dorsal fin is smaller than the first.
The bull shark has a varied diet which includes fish, other sharks, rays, dolphins, turtles, birds, molluscs, echinoderms, crustaceans, and even terrestrial mammals.
Bull sharks are mostly sluggish, solitary animals who cruise through shallow waters. They are extremely territorial creatures and once another animal - including humans - enter that territory they can become the target of often fierce aggression. They have the highest level of testosterone of any creature on the planet, even a stampeding elephant. Despite their apparent docility, they are capable of surprising bursts of speed, and can be highly aggressive, even attacking a racehorse in the Brisbane River in the Australian state of Queensland. Along with the great white, tiger and oceanic whitetip sharks, bull sharks are regarded as one of the four species that are considered the most dangerous to humans. There is no consensus, but it is believed that the bull shark is the most likely culprit of the Matawan Creek attacks of 1916.
Breeding takes place in the summer, often in the brackish water of river mouths. After a gestation of about a year, bull sharks give birth to as many as 13 live young (they are viviparous). The young are about 70 cm at birth and take 10 years to reach maturity.
|Taipan||Jan 13 2012, 08:26 PM Post #2|
Hand feeding Bull Sharks
|Taipan||Jan 13 2012, 08:27 PM Post #3|
Bull Shark Threat: They Swim Where We Swim
for National Geographic News
July 19, 2005
Bull sharks are chewing up the headlines this summer. The predators have been linked to two highly publicized attacks that left one teen dead and another seriously injured in the Florida Panhandle last month.
Though over 375 shark species have been identified by science, just three species are responsible for most attacks on humans: the great white (Carcharodon carcharias), tiger (Galeocerdo cuvier), and bull shark (Carcharhinus leucas).
Bull sharks are the least known of the three. But experts note that the species's preference for coastal waters less than a hundred feet (30 meters) deep makes bulls potentially the most dangerous sharks of all.
"Bull sharks inhabit quite shallow waters, which means that they do have a great opportunity to interact with humans, because the two species tend to share the same areas," said George Burgess, curator of the International Shark Attack File at the Florida Museum of Natural History in Gainesville.
Bull sharks are among the most common sharks in Florida waters and are often encountered by divers.
The sharks are especially at home in areas with lots of freshwater inflow, such as brackish river mouths. The abundance of such habitat along the coasts of the northern Gulf of Mexico east of the Mississippi River makes this area especially suited to the sharks.
Bull sharks happily tolerate the murky water found in estuaries and bays. Such conditions can sometimes play a role in spurring shark attacks on humans.
"Visibility is a huge factor in shark attacks," Burgess said. "That's one of the reasons we suggest that people avoid murky water situations when they go into the water."
For the most part, bull sharks dine on bony fishes or smaller sharks—but they sometimes aggressively tackle much larger prey.
"They are one of the few warm-water, coastal sharks that will attack big prey," said Mike Heithaus, a shark expert at Florida International University in Biscayne Bay. "In addition to small fish, they might attack a sea turtle, another shark, or the occasional dolphin."
"They are one of the few sharks that will tangle with prey that's the same size or even bigger than them," the marine biologist added. "Most sharks only go after prey that's substantially smaller than they are."
Bull sharks generally grow to about 7.5 feet (2.3 meters) long and weigh up to 285 pounds (130 kilograms).
Despite their healthy appetite and aggressive reputation, the animals can be rather docile in some environments. In the clear waters of the Bahamas, for example, divers regularly interact with crowds of bull sharks.
Though the predators may come in close proximity to humans, statistics suggest that swimmers, surfers, and divers have little to fear from bull sharks.
The United States averages just 16 shark attacks each year and slightly fewer than one shark-attack fatality every two years. Meanwhile, lightning kills more than 41 people each year in the coastal U.S. states alone.
While bull sharks are commonly found along coastlines, bays, and harbors, they also frequent a most uncommon shark habitat—freshwater rivers.
The species has been spotted 2,500 miles (4,000 kilometers) up the Amazon River in South America and dwell in Lake Nicaragua, a freshwater lake in Central America. Bull sharks have traveled up the Mississippi River as far north as Illinois and are regularly spotted in India's Ganges.
Their ability to tolerate freshwater is rooted in salt retention.
Sharks must retain salt inside their bodies. Without it, their cells will rupture and cause bloating and death. Given this requirement, most sharks cannot enter fresh water, because their internal salt levels would become diluted.
But bull sharks have special physiological adaptations that enable them to live in fresh water. Their kidneys recycle the salt within their bodies and special glands, located near their tails, also aid in salt retention.
While scientists have learned how the animals survive in fresh water, it is less clear why bull sharks, almost exclusively, developed this amazing ability.
Heithaus, of Florida International University, speculates that "probably the biggest reason is that [freshwater tolerance] allows the juveniles, the little guys, to be in a place that's relatively safe from being eaten by other sharks."
Adult bull sharks likely gain their own competitive advantages from salt retention. However, scientists have yet to uncover precisely what those advantages may be.
Heithaus said a big question for him is what bull sharks gave up to acquire their unique ability to survive in fresh water. "If they were a master of all trades, in both fresh and saltwater, we should see bull sharks dominating coastal waters," the marine biologist said. "There must be some cost to having that amazing ability."
Freshwater tolerance could be rooted in competition for saltwater food resources, where perhaps bull sharks suffered and needed to develop an edge. The ability might also be tied to disease susceptibility or other unknown and unstudied issues.
What's certain is that much more research is needed to understand why these unique sharks turn up in such unlikely locales as the Land of Lincoln. "It's amazing how little we really know," Heithaus said.
|Taipan||Jan 13 2012, 08:27 PM Post #4|
SHARK ATTACKS GELDING PACER
Posted by Jeremy Rangiawha 12:05 PM 24-Mar-2005 NZST
A standardbred horse in Australia was dragged underwater by a bull shark while swimming in the Brisbane River recently.
Trainer Alan Treadwell said his 6-Year-Old gelding, Glenburns Arm, was in the river when the horse "went over backwards and twisted and then all of a sudden he went berserk".
Treadwell said he was exercising his horse when a shark up to two-metres long bit the pacer on the rump.
"I saw this white thing come out of the water when he went over backwards," Mr Treadwell said.
"I kept pulling and every time he surfaced I kept dragging him in. I was getting him in slowly and when he could stand he was just trembling and carrying on – he had a white tail when he came out of the water."
Although bull sharks are relatively small – most are between just 1.5 and 2.5 metres – they can cause death by loss of blood from bites or shock.
They are found in most Australian water systems, including Sydney Harbour, the Brisbane River, the Swan River in Perth, Lake Macquarie near Newcastle and the Herbert River in North Queensland.
Mr Treadwell said the attack lasted about 30 seconds, leaving a "jaw mark", puncture wounds and bruising around the horse's leg.
"I never thought it'd happen," he said.
"I know there are little sharks there they say, but I thought, how big a shark could pull a horse down? He's 500 kilos."
Shark expert Craig Franklin said it was unusual for a bull shark to take on such a large "food item".
"It was probably a mistake," the University of Queensland professor said.
"They're opportunistic feeders, they tend to be quite aggressive sharks and it probably got a bit of a surprise to find it was quite a large food item."
Mr Treadwell said his horses would now be trained in a nearby dam.
"It's a lot safer," he said.
Courtesy Of Australian Associated Press
|Taipan||Jan 13 2012, 08:28 PM Post #5|
|Taipan||Jan 13 2012, 08:29 PM Post #6|
|Taipan||Jun 8 2012, 07:43 PM Post #7|
Giant Bull Shark Surprises Researchers
Andrea Mustain, OurAmazingPlanet Staff Writer
Date: 07 June 2012 Time: 11:45 AM ET
Dr. Neil Hammerschlag pulling up a 1,000-pound bull shark, the largest he’s ever caught. He gave the shark an ID tag and took samples from it so that scientists can learn more about it.
For scientist Neil Hammerschlag, it was just another Sunday. He was out cruising the reefs near the Florida Keys, hunting for sharks — not as trophies, but for research aimed at keeping them out of display cases and in the water. In many places, these iconic predators are disappearing.
A research assistant professor at the University of Miami, and the director of its R. J. Dunlap Marine Conservation Program, Hammerschlag spends every other weekend in southern Florida dragging baited, shark-safe lines behind a boat, hoping one of his research subjects will take a bite.
When he and his team catch one, they outfit the shark with either a satellite tag or an ID tag, take tiny samples of muscle and fin and a vial's worth of blood (they check to see if the shark is pregnant), then send the shark on its way. The whole process takes about five minutes.
On Sunday, May 27, they were having plenty of luck. Something snagged the other end of the 75-foot (23-meter) line, and Hammerschlag began to pull it in. Right away, he said, he could tell something was different.
"It's a lot of work to bring up a line, but I can usually do it myself," he says. This time, he needed help.
He and a colleague joined forces. "We didn't know if we were pulling up a sunken boat, a monster shark, a school bus — we had no idea which it was," Hammerschlag told OurAmazingPlanet.
They were in about 150 feet (46 m) of water, and, even as the two men strained to pull in whatever it was, it remained invisible, hidden by the murk of the shallow ocean.
"As soon as it came to the surface, it literally took my breath away, it was so big," Hammerschlag said. They had hooked a massive bull shark, the region's top predator; the shark was about 10 feet (3 m) long and, the researchers estimated, over 1,000 pounds (454 kilograms).
"It's one of the biggest bull sharks I've ever caught, and it's the biggest bull shark I've ever tagged," Hammerschlag said — and he's tagged more than 1,000 sharks. "When this guy rocked up, it just took my breath away."
The huge bull shark, the top predator in the Florida Keys where it was caught, turned out to be a female, which are typically larger than males.
It turned out it was, in fact, a lady. Like many other shark species, female bull sharks are larger than males. But bull sharks of either sex are nothing to be trifled with. Like great white sharks and tiger sharks, bull sharks have serrated teeth — an accessory that allows them to rip and tear apart their meals, which means they can go after far bigger prey than smaller shark species can.
Bull sharks "have the most testosterone of any animal on the planet, so that should tell you a little something," Hammerschlag said. They also like to hang out in shallow, coastal waters.
Despite what this implies for our own species, Hammerschlag said the sharks don't specifically target people. "They possess the machinery but lack the motivation," he said.
Bull sharks are one of the three species most often blamed for unprovoked, deadly shark attacks around the world, according to the National Oceanic and Atmospheric Administration.
Yet far more commonly, people attack sharks. Their fins, prized for shark-fin soup, a traditional Chinese dish, fetch high prices. According to numbers cited by the Humane Society, as many as 73 million sharks are killed for their fins each year.
Overall, many shark species are facing steep declines. Figuring out what is driving that trend, and reversing it, is a big motivation of Hammerschlag's research. "We know a lot of shark populations are in trouble, but the question is, what is happening to Florida Keys sharks?" he said. "And if you want to be effective at conserving them, what would it take?"
Because they had run out of satellite tags — they're expensive — after taking biological samples, Hammerschlag attached a simple ID tag to the bull shark. They'd have no way of tracking the giant female. With a push, Hammerschlag sent the shark on her way. He said the experience wasn't scary.
"This is a predator like none other in the world, and it deserves complete respect and attention," he said. "If your heart doesn't skip a beat, you don't have enough respect for it."
|Elosha11||Jun 9 2012, 03:41 AM Post #8|
||Thanks for posting Taipan. I saw this on underwatertimes and was going to post it as well. I'll soon be putting some new stories and images of great whites on its profile too.|
|JaM||Jun 13 2012, 02:24 AM Post #9|
Cool picture. I find it hard to believe that the shark is only 3 m. long, though. That must be fork length or precaudal length.
Ie a 4 m shark at ~600 kg would mean that a 3 m shark would be around 250 kg - after all the 4 m shark was pregnant and particularly heavy. It was 3.2 m PCL, which is body length, and it fits reasonably well with the big one above, if the length given above is either FL or PCL.
|Taipan||Oct 13 2012, 01:12 PM Post #10|
Bull sharks have strongest bite of all shark species
By Matt Walker
Editor, BBC Nature
12 October 2012 Last updated at 07:48
Bull sharks bite hard
Bull sharks have the strongest bite of any shark species, scientists have discovered.
Relative to their body size, bull sharks bite harder than other, larger predatory sharks.
Adult bull sharks can bite with a maximum force equivalent to 6,000N, a study of their jaws and jaw muscles has shown.
It is unclear why bull sharks have such strong bites, which are much greater than required to kill and eat prey.
Details of the discovery are published in the journal Zoology.
Maria Habegger of the University of South Florida in Tampa, US and colleagues in the US and Germany examined bite forces produced by 13 species of shark and their close relatives.
The species tested ranged from the 1m-long ratfish, a small relative of the sharks that scours the seabed for crabs and clams, to the great white shark, a large predatory shark that can approach 6m in length. Great white sharks feed on a variety of fish and marine mammals such as seals and dolphins.
Previous research has shown that large predatory sharks have very strong bites.
"We expect strong bite force values in the larger sharks that occupy top positions in the food chain, for example, the great hammerhead, great white shark, tigers and bull sharks," Ms Habegger told BBC Nature.
"These species usually prey upon large prey items such as dolphins, turtles and other sharks, so high bite forces are expected due to the mechanical demands of this type of prey."
But research has also shown that smaller species, such as ratfishes, have high bite forces for their size, perhaps due to their need to crush hard shells.
"So sometimes size is misleading. Although larger size sharks will exert higher values of bite force, the relative value of bite force is what matters, pound per pound how strong is the bite?," said Ms Habegger, who is studying for a PhD.
So Ms Habegger, her supervisor Dr Philip Motta, who has long studied the bite forces of sharks, and colleagues estimated the bite forces of the 13 species.
They dissected specimens to study their jaw muscles and worked out the forces these muscles can impart while closing the jaw.
The researchers then used mathematical techniques to remove the effect of body size, so they could make a fair comparison between species.
"What this study shows is that pound per pound bull sharks have the largest bite force value among all studied sharks," said the biologist.
"Bull sharks can bite harder than a great white shark and great hammerhead."
Dr Habegger says the research raises an intriguing question, however. Why do bull sharks need such a powerful bite?
The bite forces bull sharks impart change through their lifetime: smaller bull sharks actually bite harder than expected for their size, but larger individuals do not.
One idea is that this ability gives young bull sharks an advantage over other competing species; allowing them to eat more diverse prey earlier in their lives.
But overall, bull sharks, which the research shows can bite with a force of almost 6,000N at the back of the jaw and more than 2,000N at the front, seem to have bites that are too powerful.
"From our knowledge there is no need of such massive values to break fish skin or even to puncture bone," Ms Habegger told BBC Nature.
Strong jaws might be needed to crack turtle shells, as researchers still do not really understand how strong they are.
Or it could be that a strong bite is particularly useful when hunting in murky waters, such as those that bull sharks inhabit.
"In a lower visibility environment catching prey may be more difficult than in open water. So once you get a prey between your jaws, securing it is crucial to not lose your meal."
The possibility remains, though, that the huge bite forces are simply an artefact of the large size these top predators can attain.
|Taipan||Nov 20 2012, 02:27 PM Post #11|
Captive Bull Shark Kills Long-time Tank Mate
2009-03-02 15:22:43 CRIENGLISH.com Web Editor: Xu Fei
An aggressive bull shark exhibited at Shenzhen Xiaomeisha Aquarium claimed its latest victim, a lemon shark with whom it had shared a fish tank for ten years, on Sunday.
According to a Guangzhou Daily report, the 2.1 meter bull shark had a long history as a troublemaker. It began slaughtering other fish in the tank after being bought by the aquarium mistakenly as an ordinary shark in 1999. The killing spree continued for three years until it was finally recognized as a bull shark by a Hong Kong aquarium expert.
Known to scientists as carcharhinus leucas, the bull shark is considered one of the world's three most aggressive shark species along with tiger shark and great white shark.
Since 2002 the aquarium has kept the bull shark in a zone separated from other fish except the ill-fated lemon shark, which was also considered violent. But if in the following seven years visitors had wondered which of the two species was more dangerous, the question was settled on Sunday when aquarium staff found the lemon shark slain during a routine inspection.
The aquarium estimated the killing took place at about 4 am that day.
Technical staff at the aquarium told Guangzhou Daily that they would monitor the shark more closely in the future.
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