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Sample essay topic, essay writing: Hammerhead Sharks - 907 words
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Hammerhead SharksMarine Science/ Per. 1 Sharks are one of the most feared sea animals. They live in oceansacross the world but are most common in tropical waters. There are over threehundred fifty species of sharks. They can be broadly categorized into thefollowing four groups: Squalomorphii, Squatinomorphii, Batoidea, andGaleomorphii.
The shark family Sphyrnidae that includes the Hammerheads arepart of the Galeomorphic classification. They are probably the most easilyrecognizable of all the sharks. The Hammerheads are among the strangest lookingsharks. As the name indicates they have a flattened head which resembles thehead of a hammer. Their eyes and nostrils are at the ends of the hammer. Thereare many species of Hammerheads. There are eight living species of hammerheads.The following four are the main categories:1
Scalloped hammerhead (Sphyrna lewini)-Pectoral fins are tipped with blackthis grey shark. The maximum length is about 12 feet.2. Bonnethead (Spyrna tiburo)-With a head shaped like a shovel the bonnetheadrarely grows more than four feet long. This shark is commonly seen inshore.3. Smooth hammerhead (Sphyrna zygaena)-Bronze with dusky fin tips, it can growto thirteen feet.4. Great hammerhead (Sphyrna mokarran)-Attaining a length of a possible 18 feet,this is the largest and most dangerous of all the hammerheads.
One of the most interesting things about the hammerheads is the uniqueshape of their heads. Ever since scientists started to study the hammerheadthey have speculated about the use of the hammer. The hammer is a complexstructure and probably serves more than one function. The most importantfunction of the hammer according to scientists is increased electroreceptivearea and it's sensory perception. This means that the hammerhead has aremarkable sensory ability to detect the small electrical auras surrounding allliving creatures. Under certain conditions, such as in searching for woundedanimals, the electrical activity increases helping the hammerhead to feed.
Itis also believed that the hammerhead may be able to use the Earth's magneticfield as a source for navigation. Some hammerheads migrate a lot and may relyon this built in compass sense to guide them in the open ocean. Another use forthe hammer is to enhance maneuverability. The hammer's similarity to ahydrofoil seems to explain its usefulness for maneuverability and improved lift.However, this theory has not been tested. Sharks generally have a small brain in comparison to their body weight.Among sharks hammerheads have a relatively large brain-body weight ratio.Sharks differ form most other fish in several ways.
Sharks have a bonelessskeleton made of cartilage that is a tough elastic substance. Most sharks havea rounded body shaped like a torpedo. This shape helps them swim efficiently.Hammerheads are especially good swimmers because of the hydrodynamic function oftheir head. All sharks are carnivorous. Most eat live fish, including other sharks.Most sharks eat their prey whole, or tear off large chunks of flesh at a time.They also eat dying animals. Hammerheads have definite food preferences. Theirelongated head may help them locate the prey they prefer.
The Great Hammerheadlikes to eat stingrays. This was observed when the stomach contents of ahammerhead were examined and stingray spines were found. Stingrays are usuallydifficult to detect because they are partially buried in the sediment. Yet, thehammerhead is capable of finding them because they can swim close to the bottomswinging their heads in a wide arc like a metal detector. Sharks reproduce internally. Unlike most fish sharks eggs arefertilized internally.
The male shark has two organs called claspers whichrelease sperm into the female where it fertilizes the egg. In many sharks theeggs hatch inside the female, and the pups are born alive. Other species ofsharks lay their eggs outside. The hammerhead female has an internal pregnancyin which a placenta is formed around the embryo. The gestation period for mostplacental sharks is between nine and twelve months.
The placenta appears abouttwo to three months after ovulation when the embryos have consumed their yolk.Eggs are ovulated at intervals of a day or so, which explains why their may beconsiderable variations in the developmental ages of pups in a litter. It's notunusual to find embryos that have died during development. Hammerhead sharks tend to form schools of fifty to two hundred. Theytend to congregate and swim at special sea mounts. Sea mounts are underwatermountains.
In these sea mounts there are many other fish attracted by richalgae and invertebrate larvae. The hammerheads have no interest in these fish.So why do they gather at these underwater mountains? Recent research seems toindicate that hammerheads go there for mating purposes. Observations in thesesea mounts show that the majority of hammerheads there are female. Thisindicates that its easy for the male to find a mate. However, researchers weresurprised to find that there were many immature female hammerheads at the seamounts. This led them to believe that in addition to reproduction there must beother reasons for coming to the sea mounts.
It is believed that the sea mountsserve as navigational centers. Each evening the hammerheads begin a ten tofifteen mile swim away from the mount, always returning by dawn or the followingday. It seems that they spend the night at distant deep water feeding grounds.The young females participate in these long distance swims. The sea mountserves as a navigational center helping them find their way back. The nightlyswim help the young find nutritious food which helps them in their growth.Bibliography:Klimley, Peter, 'Hammerhead City', Natural History, Oct.
1995, pp 33-38. Martin,Richard, 'Why the Hammerhead?', Sea Frontiers, May-June 1989, pp. 142-145. Moss,Sanford, Sharks, Prentice-Hall, 1984. World Book Encyclopedia, Sharks, WorldBook Inc., 1988.
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