Adventure Land Travel
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Adventure Land Travel
According to the U.S. National Parks and Conservation Association (NPCA), when in shark waters but no shark is in sight, look out for fins. If you see one fin cutting through the water, that is likely to be a dolphin. Two fins - one behind the other — are more likely to be a shark, with its back and shark tail fins above the surface.
Other http://www.npca.org/ Facts:
About half the world's 350 shark species grow only to 3 feet long or less and more than 80 percent fall short of 6 feet. Only 4 percent exceed 12 feet, and three of those species feed on plankton.
The largest shark is the whale shark, a harmless giant that can exceed 40 feet (some unsubstantiated reports say 60 feet) and eats plankton and fish. The smallest is the pygmy ribbontail catshark, which grows to be less than a foot long.
In an average year, fewer than 100 people worldwide are attacked by sharks. Less than a third of these victims die. In 2000, there were 79 reported shark attacks worldwide, and 10 of these victims died.
The average North American is about 15,000 times more likely to be killed in an automobile accident than in a shark attack.
The most dangerous shark is arguably the great white, a large, aggressive predator. The second-most dangerous in U.S. waters is likely the bull shark, a large (up to 12 feet), aggressive animal that is the only shark species to regularly enter fresh water, traveling up the Mississippi River as far as the Ohio River. A third dangerous species is the tiger shark, which can grow to 20 feet. Tiger sharks sometimes eat people, whereas other species seem to attack humans primarily when mistaking them for typical prey,
Fishermen catching sharks are the most frequent victims of shark bite. Divers who swim too close or try to ride sharks are the next most frequently attacked group.
Some inshore species are top-level carnivores, feeding primariy on fishes. Their roles in reef ecosystems are not fully understood, though they may keep fish population sizes in check, and remove sick and injured fish, leaving the healthiest to survive and reproduce.
Sharks have extremely well-developed sensory capabilities. They can detect sounds and smells from prey at great distances (up to a mile or more, depending on water conditions). Their eyesight is bad, but depends greatly on water clarity.
As sharks approach their prey, they can detect the faint electric fields given off by all living organisms. Receptors on their snouts, known as ampullae of Lorenzini, allow sharks to locate their prey without seeing it.
Using these and other senses, sharks can find prey at dusk, night, and dawn, which is when some inshore species are generally believed to feed.
Sharks are very much attuned to their environment. They know when people are in the water long before people are aware of them. Encounters between sharks and people are infrequent, and most inshore species pose little threat to humans.
Although any shark may be potentially dangerous, especially if provoked, it is believed that only a few species of sharks have been responsible for biting people. However, many inshore species are difficult to distinguish from each other, and positive identification is often not made.
In cases where the offending shark can be identified, tiger sharks top the list. A tiger shark is easily recognized by its blunt snout and the vertical bars on its sides. Hammerheads are also easy to identify, and have been implicated in a few cases where they may have been provoked.
Tigers are considered the most dangerous sharks in Hawaiian waters. White sharks, which are also very dangerous, are rarely seen in Hawaii. Because of their size and feeding habits, tigers occupy the very top niche in inshore feeding relationships.
For years tiger sharks were believed to be territorial in nature. Individuals were thought to remain for the most part in a fairly limited area. Recent evidence suggests this is not the case. Tiger sharks have been found to navigate between the main Hawaiian islands, and thus appear to occupy home ranges much larger than had been previously suspected.
Tiger sharks are often attracted to stream mouths after heavy rains, when upland fishes and other animals are swept out to sea. They can easily locate prey in such murky waters. Tigers are also attracted to waters frequented by fishing boats, which often trail fish remains and blood.
Of all the inshore species, tiger sharks have the most widely varied diet. They eat fish, lobsters, birds, turtles, dead animals, even garbage, and may feed whenever a food source is present.
It’s not known why tiger sharks sometimes bite humans. The idea that they mistake a person for a natural prey item, such as a turtle, is not supported by any evidence. The shark may be trying to determine if a person is a potential prey item, it may come across a person while in a feeding "mode," or perhaps there is some other explanation.
Incidents of sharks biting people in waters are very rare. Fatal shark bites are extremely rare, especially considering the number of people in waters.
People who enter the water need to recognize that there are hidden dangers. A number of marine animals can cause serious injury to people, and sharks are just one example. Entering the ocean should be considered a "wilderness experience," where people are visitors in a world that belongs to the sharks.
The risk of injury caused by sharks is extremely small, but it is a risk accepted by anyone who enters the shark’s world. By learning more about sharks, using common sense, and observing the following safety tips, the risk may be greatly reduced.
Fact: Sharks can find prey by following the electrical impulses that animals emit, and some species of shark can smell a drop of blood in one million drops of seawater.
Fact: Sharks have an unlimited supply of teeth that are set in layered rows in the gums. If one tooth falls out, a tooth from another layer takes its place. A shark may shed as many as 50,000 teeth in its lifetime. This is one reason why prehistoric shark teeth are the most commonly found fossils.
Sharks can also detect the electromagnetic fields of the Earth and may use this ability to guide them during migration.
Sharks are often thought of as cold-blooded killers that prey on humans. However, only 32 species (out of approx. 350 shark species) have been known to attack humans, and most attacks are accidents. Often, sharks inhabit the same shallow, warm-water areas as humans. The shark may mistake a person standing or floating in water for natural prey. The shark goes in for the kill but, after one taste, usually gives up the attack.
Many shark attacks involve people trying to free sharks from fishing nets. Sharks also are territorial animals and may attack if they feel threatened. The chances of being attacked by a shark are very small, and the chances of dying from a shark attack have greatly decreased over the years. In fact, in the United States, a person is 30 times more likely to be killed by lightning than by a shark.
Sharks are fished for their fins and cartilage. Shark-fin soup is a popular food in some areas. After the fin is cut off, the rest of the shark is discarded. Shark cartilage is a subject of much scientific study because medicine made from it may stop the growth of tumors. Shark cartilage is sold in pill form as an alternative medicine. Shark finning and fishing for cartilage have caused a decline in populations in some areas of the world. Sharks mature and reproduce slowly, so it is difficult for them to rebound from a decline.
Great white shark (Carcharodon carcharias): Best known from the movie Jaws, the great white is a large, heavy-bodied shark, about 20 feet long, with large bladelike teeth. Widely the most-feared of sharks, great white attacks are rare, and most scientists agree that its reputation is undeserved. Many scientists believe it is endangered due to sport fishing and shrinking food supplies.
Whale shark (Rhincodon typus): Reaching lengths of up to 50 feet, the whale shark is the largest fish on earth. This gentle giant has small teeth like whale baleen, through which it strains small fish and crustaceans.
Tiger shark (Galeocerdo cuvier): The tiger shark is considered one of the most dangerous sharks. It is about 18 feet long and inhabits shallower water, often where people swim. The diet of tiger sharks varies widely and includes all types of sea life and even garbage.
Blue shark (Prionace glauca): The graceful blue shark is well known to scuba divers and commercial fishers - they have been seen circling divers and have followed fishing boats for days, eating stray fish.
Mako shark (Isurus oxyrinchus): Short-fin and long-fin makos are close cousins with the great white shark. They are very fast swimmers and can reach speeds of up to 60 miles per hour. Mako sharks can even leap out of the water.
Hammerhead shark (Sphyrna mokarran): Hammerheads are best known for their distinctive mallet-shaped heads and widely spaced eyes, which they swing back and forth while swimming to detect prey. They are the only species of shark known to travel in schools.
Bull shark (Carcharhinus leucas): The bull shark gets its name from its snout, which is wider than it is long. It is possibly more dangerous to humans than the great white shark because it lives in shallow, murky water in areas where people swim. The real shark attacks on which the movie and book Jaws were based were done by a bull shark.