Basic Information on Bull Shark Outline

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Bull Shark: Osmoregulator Predator Scott Marshall English Composition: EN-101-15 Professor Craig Cushing April 19, 2010 Outline Thesis Sentence: Carcharhinus leucas also known as Bull Shark are unlike other sharks as they can tolerate fresh water and can travel far upstream in rivers.

I. Introduction A. Definition of Carcharhinus leucas, its class, subclass and physiology B.

Eytmology.

II. Common Names

III. Habitat

IV. Eating habits V. Adaptability; osmoregulation

VI. Shark Attacks-Some attacks of bull sharks are blamed on the great white

A. Some statistical information

B. The 1916 New Jersey shark attacks

VII. Conclusion

A. Staying safe in the waters B. Further reading

Bull Shark: Osmoregulator Predator

The bull shark is one of the sharks that captures my interest because it can live and hunt in both oceans and rivers. The species is formally known as Carcharhinus leucas.

It belongs to a class known as chondrichthyes /kan-drik-the-ez/. This class is comprised of cartilaginous fishes with well developed jaws which include sharks, skates, rays and chimeras. (Merriam-Webster’s Medical Dictionary, Merriam-Webster, Inc. ) Cartilaginous fish means their skeleton is made of cartilage rather than bone. Kennedy, What is an Elasmobranch? ) They also belong to a subclass called elasmobranch /i-laz-me-brangk’/. (Merriam-Webster’s Medical Dictionary, Merriam-Webster, Inc. ) This sub class is defined as having five to seven gills, openings on each side of the fish, rigid dorsal fins, spiracles to help with their breathing, and scales.

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Their upper jaws are not fused to their skulls and they possess many rows of sharp teeth that can be replaced continuously. (Kennedy, About. com Guide) The bull shark is known by many names worldwide. It has the name bull shark from its appearance of a short stub nose and aggressive reputation.

Curtis) It has also been called a variety of other names ranging from Zambezi shark, Van Rooyen’s shark, Ganges shark, Nicaragua shark, fresh water whaler and estuary shark to river shark, ground shark, cub shark and shovelnose shark just to name a few. (Curtis) It gets all these names from primarily two reasons. One reason is its looks. The bull shark has a very robust body and a blunt rounded nose. They have no interdorsal ridge. They also have relatively small eyes compared to other sharks. The first dorsal fin is large, pointed and triangular, while the second is very small. Curtis) The second reason, which is more interesting to me, is the environments they have been found in. While it is not a true river shark because it cannot live permanently in the fresh water environment (K. J. O’Driscoll), the bull shark can bread, hunt and dominate in fresh water surroundings all over the world. Bull sharks live in both fresh water and salt water. They can live in rivers, estuaries and some lakes in Central America. In fact, some have been found up the Amazon River in Peru and in water over three thousand kilometers up the Mississippi River into Illinois.

Once thought to be landlocked, a whole population of bull sharks in Lake Nicaragua accessed the ocean waters through rivers. In the western Atlantic waters along the US coast, bull sharks migrate north in the summer months as far up as Massachusetts. They return to the tropical areas when the waters cool down again. (Curtis) Off the Pacific coast, bull sharks are found from southern California to the Gulf of California. (Bull Shark) Bull shark stay close to the coastlines in waters less than one hundred feet deep. They also can go as far deep as four hundred fifty feet.

What Is A Bull Sharks Diet

They often go into estuaries, bays, harbors, lagoons, and river mouths. It is the only shark species often is found in freshwater locations and can spend long periods of time in these areas. (Curtis) The feeding habits of the bull shark vary depending on opportunity, size and location. Stomach contents can be divided, in general into two different categories. One category found is food and the other inedible items. I first want to look at inedible object because they are a bit odd. Bull sharks with hooks in their bellies were examined and thought to be perhaps the remains of something else they ate such as tune that were on the hook.

After the tuna was digested the hooks remained in the sharks’ stomachs. (Maddalena) Other things considered unusual in the bull shark’s diet have been found such as algae, plants, seaweed, mud, stones, and pebbles. In some bull sharks from South Africa and other places, things have been found such as a rabbit, a mole, an antelope, cattle, sloths, rats, the head of a dog, pats of a cat and a roasted potato. (Maddalena) Food choices of the bull shark are made up of primarily bony fishes. In the Atlantic they eat mostly mullet, tarpon, catfish, menhaden, gar, snook, jacks, mackerel, snappers and other fish that travel in schools.

They also eat as part of their regular diet stingrays and smaller sharks including those of their own species. Other food found in the stomachs of bull sharks have been reported as sea turtles, dolphins, crab, shrimp, sea birds, and squid. Bull sharks tend to cruise the bottom of the water beds seeming sluggish but are in fact capable of chasing and capturing prey at speeds up to and over eleven miles per hour. (Curtis) Bull sharks are able to travel in both salt waters and fresh waters. They are able to do this because of a process called osmoregulation.

Osmoregulation is the ability to maintain a constant concentration of water in its body even when its outside environment would normally cause it to loose or gain water. (Goth) Bull sharks are not true river, or fresh water, sharks because they need salt water to survive. Without salt, shark cells will rupture and cause bloating and death. They have developed this osmoregulation process to keep the salt water concentrates in their bodies while their external environments are fresh water. They process, that all freshwater animals including fish, mammals, reptiles and amphibians do by the way, is to produce large volumes of diluted urine.

Another way this can be done is through the food they eat. The bull shark’s body has a salt replacement devise that takes the salt from food or external surroundings and moves it into the intestinal fluid and the blood. (K. J. O’Driscoll) The kidneys absorb the salts that are needed and the water is waste. The kidneys of the bull shark are remarkable because they allow the bull shark to move gradually into fresh water from salt water by less salt and more urea from the bloodstream through urination. Their kidneys recycle the salt within their bodies and special glands, located near their tails, aid in salt retention as well.

Some have speculated this may be from migrations from the oceans to an estuary and then upstream. (Goth) This makes the bull shark a very serious and dangerous risk to human bathers. To give you an idea of what range of danger we are talking about in terms of bull shark attacks, we should look at some statistics. Let’s look the big three, as called by the Florida Museum of Natural History, which include the great white (carcharodon carcharias), the tiger shark (galeocerdo cuvier) and the bull shark (carcharhinus leucas). Curtis) Bull sharks along with Tiger sharks and Great White sharks are among the three species of sharks most likely to attach humans. Attacks from around the world from 1580 to2008 (non air-sea disaster unprovoked attacks) are two hundred forty four for the great white with sixty five of those accounted for as fatalities, eighty eight for the tiger shark with twenty seven of those accounted for being fatalities, and eighty two for the bull shark with twenty five of those accounted for being fatalities. (Curtis) One always has to be cautious when looking at statistical information especially of this nature because the shark has the otential to be misidentified or unidentified in the heat of the moment or not even reported at all. According to Sharkattacks. com, United States has the highest incident of shark attacks in the world with Africa, Central America, South America, Australia and the Pacific Islands following after the US to make the list of the top five places worldwide. (Statistics versus Myths) The worst shark attack in United States history was said to happen along the New Jersey shore line in July of 1916. There were five attacks over a ten day period and four of them were fatalities.

The great white shark was blamed for these attacks because a young one was caught and was said to have human remains in its belly. The attacks were reported to have ceased with this capture, but there is controversy about weather this was really the culprit of these attacks or was it a bull shark? Maybe it was both? This debate is due largely to the fact that three of the attacks took place two and a half miles up tiny Matawan Creek where it is fresh water and murky, not the right habitat for the white shark, but it is for the bull shark.

The other two attacks took place up to seventy miles away from the creek in the ocean shore. The other issue that contributes to this idea of a bull shark being ultimately responsible for at least a few of these deaths is that two days later, The newspaper reported that there were multiple sharks alive in the creek as told by men hunting for sharks there. Finally, three days later it was reported that a giant shark jumped the chicken wire fence in the creek and swan off into the ocean which is very typical behavior of bull sharks. The case of the New Jersey Man-Eater) The bull shark has been considered by many experts to be the most dangerous shark in the world. (Curtis) The problem is because they are found in great abundance near human populations especially in the tropics and their ability to travel in fresh water arenas where humans play giving them ample contact with us. There are things we can do to stay safer in the waters. River mouths should be avoided when swimming where there are cloudy murky waters. Swimming should be avoided near schools of fish in inshore area.

Use extreme caution when spear fishing as bull sharks are known for their attraction to spear fishermen. (Curtis) Never swim alone. Sharks like single targets. Don’t go in deep. Stay away from swimming at dusk and dawn as humans see less and sharks see more. Don’t go into the water if there is blood for obvious reasons. Don’t wear jewelry because sharks are known to be attacked to shiny fish. Don’t panic. Just leave the water quickly and quietly if you see a shark. And finally do not swim in area where there have been other shark attacks. (Shark Attacks)

If you are interested in more in depth or further research and information there is a new book written by Ralf Collier, entitled Shark Attacks of the Twentieth Century, from the Pacific Coast of North America. (The case of the New Jersey Man-Eater) You can also find information at the International Shark Attack File from the University of Florida, USA. (Shark Attacks)

References

2010. <www. sharks. org. za>.

Burgess, G. “The 1916 New Jersy Shark Attacks, the Worst in US Histroy. ”

2010. SEMP INC. April 2010 <www. semp. us>. Curtis, T. Florida Museum of Natural History Ichthyology Department.

April 2010 <www. flmnh. ufl. edu>. Elasmo Research. 2010 <www. elasmo-research. org>. Goth, A. Shark Savers. April 2010 <www. sharksavers. org>. Handwerk, B. National Geographic News. 19 July 2005. April 2010 <news. nationalgeographic. com>. O’Driscoll, K. J. , Staniels, L. K. and Facey, D. E. “8. ” Osmoregu;ation and Excretion. <www. cartage. org. lb>. Kennedy, J. About. com Guide. April 2010 <marinelife. about. com>. Marine Life. April 2010 <marinelife. about. com>. De Alessandro, M.. SHARKS The Perfect Predators.

Sunnyside, Aukland Park: Jacana Media (Pty) Ltd, 2008. Marine Bio. April 2010 <marinebio. org>. Merriam-Webster’s Medical Dictionary, Merriam-Webster, Inc. Dictionary. com. 2007. April 2007 <dictionary. reference. com>. NOAA FISHERIES FACT SHEET. April 2010 <www. nmfs. noaa. gov>. Pillans, R D. UQ eSpace. 2006. April 2010 <espace. library. uq. edu. au>. Shark Attacks. April 2010 <www. bugbog. com>. Statistics Versus Myths. April 2010 <www. sharkattacks. com>. The case of the New Jersey Man-Eater. April 2010 <www. elasmo-research. org>.