Caribbean Reef Shark's FINAL
This discussion topic submitted by Andrea Knoch (
Scratch809@hotmail.com) at 3:34 pm on 6/8/00. Additions were last made on Thursday, June 8, 2000.
The Caribbean Reef Shark
The Caribbean reef shark, carcharhinus perezi, aroused my interest of research after seeing its picture. Of all the marine organisms potentially dangerous to man, none are so universally feared and respected as are sharks. This is due to human kind knowing so little about their life in the wild.
It has taken 400 million years for jawless fish to evolve into the flesh-shredding sharks we know today. There was little knowledge of the evolution of sharks until an amateur archeologist found fossilized remnants of a shark in an ancient mud bed south of Cleveland Ohio in the late 1880's. From the first findings until now, we have separated sharks into 19 family classifications, and 368 species.
Certain facts should be kept in mind when attempting to identify sharks. However, body proportions, fin size, location, and other features are somewhat inconsistent. Many of the body features and dimension as well as coloration change with the shark's growth. Coloration is the LEAST consistent for identification in most cases as coloration depends on environmental and dietary habits. There are three factors for identification in each species of shark, fin size, weight, and liver oil proportions. Liver oil proportions permit a shark to control the depth at which it swims.
The Caribbean reef shark can be identified against other sharks by its relatively large eyes, distance between pelvis and anal fins being less than 3/4 length of anal fin base, and length of second dorsal being greater than its height. It grows from a birth length of 38 inches to adult length of 8 feet, in its life span of 25 years Being an olive-gray, and paler shades of yellow gray, it can be found on the inshore reef, Bahamas banks, West Indies, and the SE Florida coast (Pope). These sharks are usually seen actively swimming in the open ocean, but in the caves, they are on the bottom, 20m down, motionless.
Many sharks have a skeleton of flexible cartilage, reinforced with some mineral deposits. Cartilage is beneficial to shark instead of bone because it is much less dense. Outside of the cartilage, there is a skin that is similar to that of man. The skin is similar to that of man because of its outer epidermis, which can regenerate itself, like our skin, and the second layer called the dermis. The dermis provides pigmentation of the hide. The epidermis is covered with placid scales called dermal denticles, which are like thousands of minute teeth firmly embedded in the skin. These sandpaper texture tiny scales possess a root canal, bloods vessels and nerves. There is a wide array of denticle sizes that can be found in serried ranks, or may be spread more dispersely. In some spaces the denticles are rounded, smooth and with out points.
The eyes of a shark have an upper and lower eyelid, but have little movement. Being moderately far sighted, the Caribbean Reef Shark is able to view 50 feet in front of them, but are color blind. Viewing their range of eyesight, and moving to different depths, maximum dilation and constriction take about a minute, which is much faster than humans. However, seawater absorbs most colors rapidly, and vision and sensitivity to color my not be as important to sharks in detecting prey as their senses of smell and hearing.
The breathing process of a shark begins by swimming with its mouth open, allowing water to enter. With the throat blocked by muscular tissue, the water exits through the external five-gill slits or clefts on each side of its head. At the same time that the water is rushing through the gills oxygen is extracted and absorbed into the blood. Simultaneously, carbon dioxide is released from the blood into the water.
The tail plays a major role in providing the power for swimming, and provides for sudden changes of direction. Sweeping from side to side, the fin produces a sculling motion. Unlike most fish, sharks have no swim bladder. This makes them are denser than water and for that reason, must constantly be swimming to avoid sinking. The sharkÝs liver also counteracts the tendency to sink. Occupying 90% of the body cavity, the liver has lighter than water oils which decreases the density of its body. Constantly moving provides a steady stream of oxygenated water to the gills. For this reason, some swim as far as 35,000 miles yearly. Their color will change when swimming from deep to shallow water from a deep gray or black to pale brown of or gray.
Sound is a means of locating prey, and sharks are able to hear the lower sounds 1000Ýs of yards from their location. They have an internal ear on each side of their head along with a lateral-line system that extends along the sides of their head and body. The lateral line consists of fluid-filled sensory canals that contain receptors sensitive to vibrations, pressure changes and waves and movements in the water.
During the breeding season, many females are seen with torn and scarred fins, from male teeth marks. The reproduction of sharks is through the female being internally fertilized. This process of internal fertilization is through insertion of the males claspers in to the cloaca (anal opening) of the female. The time required form conception to birth is 12 months, and shape of the eggs, laid in pairs, will vary from rectangular to ovular. Reproduction -, during the breeding season, nay females are seen with torn and scarred fins, the better developed teeth in the males of some species may be an adaptation connected with copulation which takes on average half an hour.
The teeth become important tools in the ultimate identification of any sharkÝs species, genera or family due to being different shapes and sizes. There are two types of teeth; incisors are for cutting and molars are for crushing. The transition from incisors to molars is very gradual and the upper jaw generally differs from the lower. Sharks, like humans, have teeth that are not implanted in sockets but are attached at their bases to a connective tissue, and anchored by a root. Frequently loosing and breaking teeth, sharks have what are called functional teeth. Functional teeth are several rows, commonly 5-7, under the gum tissue that are able to replace at a momentÝs notice. When a tooth is broken or lost, then next tooth in position behind it begins to move up and forward filing in the space. Replacement of the lower takes 8 days and upper 7 days. The teeth are replaced so quickly that an individual shark may shed as many as 30,000 teeth during its lifetime.
Nothing is more unpredictable than a sharkÝs behavior in face of food. Sharks are extremely efficient when it comes to finding food because they can hear things that are thousands of yards away and detecting pray by sight, smell, sound, touch, taste, water vibrations, and electric fields.. Recent heavy rains attract the shark due to the washing down of dead animals. However, their appetite is quickly satiated because its only once or twice a month that they are able to eat an ill or dead dolphin, and the rest of the time they just have the residue from births or other leavings. Sharks consume food equal to 3-14 percent of their body weight within one week.
The stomach of a shark is in the shape of a U and are therefore not coiled like that of humans. Having the intestines relatively short helps to digest food quickly but creates a problem with the rate of absorption, which the stomach mussels help with.
Sharks can sense one part mammal blood to 100 million parts water. However, individuals have a 1 in 5million chance of being attacked by a shark. There is a better chance of being struck by lightening. Several sharks considered dangerous, but have few recorded attacks and far fewer fatalities, are the gray reef shark, blacktip reef shark, reef shark. They are unagressive in situations where they meet divers, but will retaliate vigorously if they are disturbed, speared, or provoked. A common thought is that the youngest sharks, the smallest, are the most brazen. Even a very small shark, two feet in length can inflict dangerous wounds.
Sharks are extremely sensitive to odors of blood and are accustomed to attacking anything that floats. For divers the moments of entering and leaving the water are particularly dangerous since only a third of shark attacks occur in water deeper than 5 feet. However, sharks will never attack a diver below the surface immediately. They will circle around the individual, go away and then cautiously return. This gives the diver time to decide whether to remain or return to the surface. In clear water, and daylight a diver is in little danger if they encounter a shark, but it is dangerous to dive at night. Not only is it dangerious to dive at night, but to show fear of a shark, because he knows this by instinct, and can profit from it. The best protection lies in ease of movement in diving, swimming slowly and softly, and avoiding abrupt change of position. If a shark should swim toward you, try not to swim away but face them calmly
There still exists no effective mans of keeping sharks away from the area in which you re diving, either by chemical products, sound waves or fields of electricity. "All things considered, diving in tropical waters is actually much less dangerous than riding a motorcycle" (Cousteau 240). Percautions to take are to always swim with a partner. If wearing scuba, its best to remain submerged in the water until you have reached the boat because sharks make the connection of fishing boats and the presence of fish at the end of the lines. Do not deliberately grab, injure, or provoke even a small seemingly harmless shark. Amongst the causes of premature death, sharks must be ranked far below cars, motor cycles, alcoholism, excessive smoking, and narcotics.
Budker, Paul. The Life of Sharks. New York: Columbia University Press, 1971. 41-101
Cousteau, Jacques-Yves, and Philippe Cousteau. The Shark" Splendid Savage of the Sea.
Farden City, New York: Doubleday & Company, Inc.,1970. 229-240.
Faughnan, Victor R. The National Shark-O-Pedia. Honolulu, Hawaii: Uudersea
Resoueces, Ltd,. 1980. 1-9.
Gold, Joy P., and Victor G. Springer. Sharks in Question. Washington, D.C.:
Smithsonian Institution Press, 1989. 51-94,
Harrigan, Bill. "Shark Diving Bahamas Style." Bahamas Diver 1998/1999: 10-12.
Pope, Patricia E. A Dictionary of Sharks copyright 1973 Great Outdoors Publishing
Company St. Petersburg, Florida. 5-7, 78-86.
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