Quote:
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Originally Posted by TeCHniX
Of course not, he'd rather not be in a coma.
HIJACK'D.
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that's not how you hijack a thread, this is how you hijack a thread:
THIS THREAD IS NOW ABOUT SHARKS
Sharks have keen olfactory senses, with some species able to detect as little as one part per million of blood in seawater. They are even more attracted to the chemicals found in the gut of many species, and often linger near or in sewage outfalls. Some species, such as Nurse sharks, have external barbels that greatly increase their ability to sense prey. Shark eyes are similar to the eyes of other vertebrates, including similar lenses, corneas and retinas, though their eyesight is well adapted to their marine environment with the help of a tissue called, tapetum lucidum. This tissue is behind the retina and reflects light back to the retina, thereby increasing visibility in the dark waters. The effectiveness of the tissue varies, with some sharks having stronger nocturnal adaptations. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some have nictitating membranes. This membrane covers the eyes during predation, and when it is being attacked. Sharks generally rely on their superior sense of smell to find prey, but once they are close they also use the lateral lines running along their sides to sense movement in the water and also employ special sensory pores on their heads (Ampullae of Lorenzini) to detect electrical pulses created by the muscles of prey. Their teeth are not attached to the jaw, but embedded in their flesh, and in many species are constantly replaced throughout the shark's life. The lower teeth are primarily used for holding prey, while the top are used for cutting into it. (Gilbertson, 7.3)
There are exceptions to the "large", "marine" (as in 'ocean-going') and "predatory" portions of the characterization. Sharks include everything from the hand-sized Pygmy Shark, a deep sea species, to the Whale Shark, the largest fish (although sharks are not closely related to bony fish) which is known to grow to a maximum length of approximately 15m (49 feet) and which, like the great whales, feeds only on plankton. Although not unique among sharks, the Bull Shark is the better known of several species to regularly swim in both salt and fresh water environments (most famously in Lake Nicaragua, in Central America) and in most deltas. A few of the larger species, the Mako and White Shark, are mildly homeothermic, able to maintain their body temperature at a level above the ocean's temperature. This is possible because of the presence of the rete mirabile, a counter current exchange mechanism that reduces the loss of body heat.
Like other fish, sharks extract their oxygen from seawater as it passes over their gills. Due to their size and the nature of their metabolism, sharks have a higher demand for oxygen than most fish and they cannot rely on ambient water current to provide an adequate supply of oxygenated water. If a shark were to stop swimming, the necessary water circulation for respiration would become too low and the animal could suffocate. Some sharks, like the Blacktip Reef Shark and Nurse Shark, can pump water over their gills as they rest. There are also known instances, such as in certain caves along the Yucatan coast, where sharks of varying species rest on the cave floors and allow the fresh water outflow to pass over them. The outflow is strong enough to allow for respiration, and it is believed that the reason for this behaviour is that the fresh water helps remove certain parasites. Also, unlike other fish, sharks do not have gas-filled swim bladders, but rather rely on an oil-filled liver for (limited) buoyancy, so they sink when they stop swimming; a resting shark always sinks to the sea bed.
A shark, if inverted, enters a natural state of paralysis. Researchers use this condition for handling sharks safely.
A popular myth is that sharks are immune to disease and cancer, however, this is untrue and there are both diseases and parasites that affect sharks. The evidence that sharks are at least resistant to cancer and disease is mostly anecdotal and there have been few, if any, scientific or statistical studies that have shown sharks to have heightened immunity to disease. [1]
Urine in sharks accumulates in the blood and is then secreted through the skin.
The fear of sharks has been fueled worldwide by a few unusual instances of unprovoked attack, such as the Jersey Shore Shark Attacks of 1916, and by sensationalized fiction and film, such as the Jaws series. While sharks cause a few dozen human deaths annually, it is relatively not a large number (e.g. several hundred people die anually struck by lightning; however, lightning may strike anywhere worldwide, whereas only a very small part of human population is susceptible to shark attacks, i.e. only those people who enter the water in the areas populated by sharks).
Contrary to popular belief, only a few sharks are dangerous to humans. Out of the more than 360 described species of sharks, only 4 have been confirmed to have killed humans: the Great White, Tiger, Bull, and Oceanic Whitetip sharks. These sharks, being large, powerful predators perfectly capable of eating humans, will sometimes attack and kill people, but all of the above sharks, even the Great White, have been filmed in open water, with no cage, time and time again, without incident. There are many theories about why sharks attack people. Some claim that the shark is confusing a human for a seal or other prey animal; this would be typical in the case of an attack against a surfer. Often the shark that attacks a human will make only one bite and then go away. This behaviour has many possible explanations, one being that humans don't taste good (or at least, as good), or are lacking the necessary fat, and another being that sharks normally make one swift attack, and then retreat and wait for the victim to die, or exhaust itself, before it comes back to feed. This protects the shark from retribution from a wounded and aggressive target, but also allows humans the time to get out of the water and survive.
A number of other species (perhaps 10 - 15) have threatened, attacked, and/or bitten (but not killed) humans without being obviously provoked. This group contains the Mako, Hammerhead, Gray Reef, Black Tip Reef, Lemon, Silky and Blue sharks. These sharks are also large, powerful predators which can be provoked simply by being in the water at the wrong time and place, but they are normally considered less dangerous to divers and swimmers than the previous group. In most cases, if a person moves away calmly, or remains still, they will be ignored. Many shark species are known to "display" when feeling threatened, and it is ill-advised to remain in the vicinity at such a time as this would generally be considered enough provocation to warrant an attack.
A few other shark species do attack people every year, producing wounds that can potentially kill, but this occurs either specifically because they have been provoked, or through mistaken identity due to water conditions or the like.
Sharks belong to the superorder Selachimorpha in the subclass Elasmobranchii in the class Chondrichthyes. The Elasmobranchii also include rays and skates; the Chondrichthyes also include Chimaeras. It is currently thought that the sharks form a polyphyletic group: in particular, some sharks are more closely related to rays than they are to some other sharks.
There are more than 360 described species of sharks.
The first sharks appeared in the oceans 400 to 350 million years ago. Most of the species we know today are as old as the Jurassic period. There are eight orders of sharks, listed below in roughly their evolutionary relationship from more primitive to more modern species:
* Hexanchiformes: Examples from this group include the cow sharks, frilled shark and even a shark that looks on first inspection to be a marine snake.
* Squaliformes: Examples from this group include the bramble sharks, dogfish sharks and roughsharks.
* Pristiophoriformes: These are the sawsharks, with an elongated, toothed snout that they use for slashing the fishes that they subsequently eat.
* Squatiniformes: Angel sharks.
* Heterodontiformes: They are commonly referred to as the bullhead or horn sharks.
* Orectolobiformes: They are commonly referred to as the carpet sharks, including zebra sharks, nurse sharks, wobbegongs and the largest of all fishes, the whale shark.
* Carcharhiniformes: They are commonly referred to as the groundsharks, and some of the species include the blue, tiger, bull, reef and oceanic whitetip sharks (collectively called the requiem sharks) along with the houndsharks, catsharks and hammerhead sharks. They are distinguished by an elongated snout and a nictitating membrane which protects the eyes during an attack.
* Lamniformes: They are commonly referred to as the mackerel sharks. They include the goblin shark, basking shark, megamouth shark, the thresher sharks, mako shark and great white shark. They are distinguished by their large jaws and ovoviviparous reproduction.
The Lamniformes include the extinct Megalodon (Carcharodon megalodon), which like all extinct sharks is only known from its teeth (the only bone found in these cartilaginous fishes, and therefore the only fossils produced). A reproduction of the jaw was based on some of the largest teeth (up to almost 17 cm (7 inches) in length) and suggested a fish that could grow 15 m (50 feet) long. The jaw was realized to be inaccurate, and estimates revised downwards to around 6 m (20 feet).
Each year, 100 million sharks are killed by people in commercial and recreational fishing. In the past they were fished simply for the sport of landing a good fighting fish (mako sharks for instance). Sharkskin (covered in effect with tiny teeth - dermal denticles) was used for the purposes that sandpaper currently is, others for food (Atlantic thresher, mako and others), and some species for other products.
Sharks are a common seafood in many places around the world, including Japan and Australia. In the Australian State of Victoria Shark is the most commonly used fish in fish and chips, in which fillets are battered and deep fried or crumbed and grilled and served alongside chips. When served in fish and chip shops, it is called Flake.
Sharks are often killed for shark fin soup, in which many sharks are hunted for their fins, which are cut off with a hot metal blade before the live animal is tossed back into the water. There have been cases where hundreds of de-finned animals were swept up on local beaches without any way to convey themselves back into the sea. Conservationists have campaigned for changes in the law to make finning illegal in the U.S.
Sharks generally reach sexual maturity slowly and produce very few offspring in comparison to other fishes that are harvested. This has caused concern among biologists regarding the increase in effort applied to catching sharks over time, and many species are considered to be threatened.
Organizations like the Shark Trust are trying to limit shark fishing.
Jan 07, 06
