Sharks Final

This topic submitted by Rebecca Cummins at 1:19 PM on 6/10/04.

Students hard at work on the "Mangrove Challenge"! (Sierpe River, SW Costa Rica)

Tropical Field Courses -Western Program-Miami University

Throughout time, one of the greatest fears of the deep blue ocean has been the shark. But little do people know that sharks come in all different varieties and some are even more scared and curious of us as humans than we are of them. The three sharks that I learned about and found to be very interesting were the black tipped reef shark, the white tipped reef shark and the tiger shark. Although they are all sharks, they are all very different in a lot of ways as are all sharks.
The black tipped reef shark, scientific name carcharhhinus melanopterus, are not known to be that dangerous to divers, unless provoked, but have been known to be dangerous in waters where there are waders. For instance, where there is a dock and people may hang there feet over, the shark may mistake it for prey and attack. “To avoid the blacktip, marshal islanders preferentially swim rather than wade when crossing atoll passes” Springer and Gold, 129. So they have become known for their attacks. They have become famous for entering the shallow waters where their black-tip is visible. “It has been seen in such shallow water that it has had to wriggle across the seafloor with much of its back exposed” Carwardine and Watterson120. The black-tipped reef shark often gets confused with the black-tipped shark that can leap out of the water and spin before landing back in it. The blacktip is slightly larger, has a smaller black tip on its first dorsal fin and a longer, more pointed snout” Carwardine and Watterson 120.

“Most prominent feature- The tips of all fins are ink black, the middle half of the first dorsal fin is a lighter shade of the darker body color

Color- Various- Shade of brown coffee cream brown, above; undersides are white. A dark band of upper body color extends backwards on both sides and a band of white of the underside extends forward and above it

Size- Lengths of six feet. Are common; large individuals of ten feet. have been reported, although this is questionable. Maturity is reached at about four to five feet. Adults may exceed 100 pounds in weight

Reproduction- Fertilization is internal. Gravid females may bear less than a dozen embryos in a liter. The gestation period seems to be about twelve months. The young are born alive and free swimming and are about twelve to fourteen inches in length

Diet- Consists of various smaller reef fishes including eels, squids, octopuses, and crustacean (crabs, lobsters. etc.)

Danger Rating- Young individuals display a somewhat shy timid behavior coupled with a nature. Despite their apparent docile character at least unprovoked attack on man is on record

Economic importance- None

Related species- None. Easily distinguished from other black-tipped sharks

Physical Features peculiar to this species-
1. The tips of all fins are conspicuously ink black
2. A dark band of upper body color extends backward on both sides and a band of white on the underside extends forward and above it
3. The snout is blunt and rounded
4. Caudal fin is asymmetrical
5. The first dorsal fin origin is even with or slightly behind the pectoral fins trailing edge
6. There is no ridge present on the midline of the back
7. The caudal fins leading and trailing edges have heavy ink-black margins
8. The eyes posses a nictitating membrane, there are no present” Faughnan 20.

The white-tipped reef shark, scientific name triaenodon obesus, is known to be found around the Red Sea, the Indian Ocean, the Philippine Islands and the Marshal Islands. They do not pose a real threat as far as attacks go due to their size and the size of their teeth; the most threat they pose is their liver. If they were to be eaten they would be most dangerous because their liver is poisonous. They do hang around the seabed’s a lot and are very slow so divers will have a great chance of swimming into one or to since they do lie together unless it is feeding time. White-tipped reef sharks are not the best at catching prey however; they even have their own predators, such as larger sharks. “Unlike most other requiem sharks, they are not good at catching prey animals in open water and tend to specialize in extracting them from their resting place. They may break apart coral heads, or wriggle into crevices to get reef fishes and invertebrates” Carwardine and Watterson130.

“Most prominent feature- both dorsal fins and the upper lobe of the caudal fin are conspicuously white-tipped, the first dorsal and upper caudal fin are most prominent

Color-various shades of grey, slate grey to dark grey, the undersides fades to white often the body is sparsely covered with dark spots along either side

Size- lengths of seven or eight feet are not uncommon for this species. Maturity is reached at four to five feet. Fully-grown adults mat exceed one hundred pounds in weight.

Reproduction- Fertilization is internal, smaller broods of perhaps eight or less likely. The young are born alive and free swimming. The gestation period is about ten to twelve months

Diet- Its haunts are haunts are both the bottom and inshore reefs which suggests a varied diet; large and small reef fishes eels, octopuses, crustacean (crabs, lobster, etc.) as well as some rays

Danger Rating- As with some docile natured sharks, it is considered by many to be harmless. This shark, as with most animals, will, when provoked or threatened defend itself. The liver of this species is said to be toxic and therefore should not be consumed by humans

Economic Importance- None

Related species- None. The three other sharks displaying white-tips are the oceanic white-tipped shark, the silver white-tipped shark, and the inshore white-tipped shark

Physical features peculiar to this species
1.Both the dorsal fins and upper lobe of the caudal have white tips
2. The snout is short and blunt as well as somewhat depressed
3. The nostrils have prominent flaps
4. The second dorsal fin is about half the size of the first
5. The sides of the body of sparsely covered with dark spots or blotches
6. The caudal fin is asymmetrical in shape
7. The eye posses a nictitating membrane and spiracles are present behind the eyes” Faughnan 33.

The tiger shark, scientific name galeocerdo cuvier, is one of the most dangerous sharks in the open ocean. In young, immature tiger sharks, they are distinctly marked with dark grey to black spots, which as they mature turn into vertical stripes. In some, even most, they fade out completely. The tiger shark is known to be the most dangerous shark in the tropics. It has a reputation as being a man-eater, and even eating anything it can get its teeth on. “It attacks anything that falls into that floats or is thrown or falls into the sea” Springer and Gold 127. The tiger shark, when studied, has been found to have anything from human limbs to cans. The tiger shark can eat right though a sea turtle. They are often seen near the shore, but recent studies have found them to be out in the open ocean more also. Tiger sharks serve a great economical importance for the West Indies. Not only do they provide food, but also their skin and teeth are used. The most interesting piece of information that I obtained was the tagging of tiger sharks. I read “of 1,321 tiger sharks tagged from 1980-1987 by the National Marine Fisheries Service, only 56 have been recaptured. One Shark tagged off Alabama was recaptured 65 months later off Cuba, approximately 1,000 km away while a sharks tagged off New York was recaptured 6 months later off Costa Rica, almost 3,00 km away, three sharks tagged off New Jersey and Virginia wee recaptured from 2-31 months later off North Carolina (by the same fisherman at the same place!), 260 km to 630 km away” Smithsonian Gold 128. I found this to be very interesting how the tiger shark varied fro the white-tipped reef and black-tipped reef shark that seemed to stay put in the seabed.

“Most prominent feature- Body marked with vertical blotches or bars (stripes) from gill area to upper lobe of caudal fin. Very prominent in young; weak or absent on large adults

Color- Gray to grayish-brown above; upper portion of body is usually darker than sides with white undersides

Size- Reported to reach lengths of thirty feet; such lengths remain to be authenticated. Known to attain lengths of twelve to fourteen feet with authenticated lengths of fifteen to eighteen. Adults capable of weights of excess of 1,500 pounds. Maturity attained between ten to eleven feet, though gravid females from twelve to thirteen feet are more common

Reproduction- Fertilization is internal, a profile shark; females capable of bearing large litters of broods of up to fifty or more embryos. One specimen recorded contained eighty-two embryos. Gestation period of two years is likely. The young born alive and free-swimming, are about twenty-four inches in length

Diet- apparently prefers slow-swimming marine life such as puffer fish and sea turtles. Definitely a feeder of opportunity; will readily sample as food simply anything that presents itself. The stomachs of specimens examined contained the following items;
Other sharks- whole or parts, various fishes- large and small, sea turtles, porpoise, portions of whales, cats, dogs, cattle, sheep, rats, birds, chickens, horses, sea lions, as well as remains of human beings. Tigers consume an endless list of trash and garbage; wire, tin cans paper plastic, wood, nails, rocks (coral), clothing, fishing gear, and other paraphernalia. In short, it is a scavenger in the truest sense of the world

Danger Rating- Highly dangerous, a reputed man-eater; will sample man with little or no hesitation. Capable of dismembering a man of considerable girth easily. A sluggish swimming shark when not feeding, but once excited by the scent of food or the erratic behavior of wounded fish it becomes very fast and aggressive. This species is guilty of a great number of attacks on humans throughout the warmer waters of the world

Economic Importance- The flesh of young Tiger sharks is used as food; however, larger Tigers are not considered desirable. Hide is used commercially for leather; and is considered the most desirable of leathers. Liver was used at one time for extracting vitamin A. The jaw is capable of producing some one hundred teeth sometimes used in making unique jewelry. Recognized by the International Game Fish Association as a game fish. The present record on rod and reel for a Tiger shark is: 1,780 pounds; its length was 13 ft. 101/2 in. with a girth of 8ft. 7in. Walter Maxwell caught it at Cherry Grove, South Carolina on June 14, 1964 on 130-pound test line

Related Species- None.

Physical features peculiar to this species
1. The body is marked with dark vertical blotches or bars (stripes) from gill area to upper of caudal fin.
2. The snout is short, wide and prominently blunt as seen from above
3. A prominent mid-dorsal ridge is present on the midline of the back between both dorsal fins
4. A well pronounced primary keel is present on both sides of the peduncle
5. The caudal fin is asymmetrical in shape
6. A well-developed lip or groove is present on underside of the snout
7. A small, inconspicuous spiracle-slit is present behind both eyes.
8. The teeth are unique, cock-comb in shape; the central cusp is triangular with large serrations and notches on one side with large serrations.
9. The eyes possess a well-developed nictitating membrane” Faughnan16.

After doing my research, I have found sharks to be very interesting creatures. There are many varieties of sharks swimming around in the deep blue ocean and I do hope to see one in the Bahamas, just not a Tiger shark. Not all sharks are man-eaters and most are just as curious about us as we are about them. Take the White-tipped reef shark for instance, unless provoked or eaten, our chances are slim of being attacked. On the other hand, we do have the “Great White of the tropics”A.K.A. the Tiger shark, who would eat just about anything. But I learned that the different varieties have different purposes.

The Shark Watchers Handbook. Carwardine, Mark and Ken Watterson. BBC World Wide Ltd, 80 Wood Lane. London. 2002.

The Life Of Sharks Budker, Paul. Weidenfeld and Nicolson. London. 1971.

The Shark Watchers Guide Dingerkus, Guido. Julian Messener. New York. 1985.

The National Shark-O-Pedia. Faughnan, Victor R. Undersea Resources, Ltd. Hawaii. 1980.

Sharks and Survival. Gilbert, Perry W. D.C. Heath and Company. Boston. 1963.

Sharks in Question: The Smithsonian Answer Book. Springer, Victor and Joy P. Gold. Smithsonian Institution Press. Washington, D.C. 1980.


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