Name ______Period ______Date______
Aggressive Sharks: Great White & Tiger Sharks
Great White SharkMarine life is rather intriguing considering the sizes, shapes and colors of the varied species of fish. Amongst all of them, one of the most dreaded is the entire range of shark species. They are dreaded because of their violent temperament. They do not appreciate human beings swimming into their domain. One species of the shark clan is the great white shark that swims around the coastal regions of the all the oceans. These sharks are also known as white pointer, white death, as well as white shark. The scientific name of this shark species is Carcharodon carcharias. The white sharks are the largest predatory fish in the world. It is the only species of the genus Carcharodon that has survived the ravages of time. The rest of the species have gone into extinction.
The great white sharks are extremely sensitive to the electrical field emitted by the movement of living creatures. Their sensitivity is due to the extra sense that was given by the Ampullae of Lorenzini (an organ used to sense vibrations and electrical fields in the water). The sharks are so sensitive that they can perceive half a billionth of a volt.
/ These sharks primarily inhabit coastal regions where the water temperature ranges between 54 degrees F to 75 degrees F. However, they are found in large numbers around the southern coast of Australia, California, South Africa, Isla Guadalupe (Mexico). The maximum population inhabits the coastal region around the Dyer Island in South Africa.It was usually believed that the white sharks are not very social. However, recent researches have proven that this species is rather social. The sharks of South Africa apparently follow what is known as a dominance hierarchy based on size, genders and the rights of the squatters. The smaller sharks are dominated by the larger ones. The Newcomers are dominated by the resident sharks. They tend to resolve all their problems through the rituals they follow.
The Great White is between 12-16 feet long, and can grow up to 19-21 feet. There is another main reason why the Great White is the most feared fish for humans. Great White Sharks are a very large species of shark. They are streamlined swimmers, and have a torpedo-shaped body with a pointed snout. They have about 3000 teeth, arranged in several rows. The first two rows of teeth are used for grabbing and cutting prey, while the teeth in the last rows rotate into place when front teeth are broken, worn down, or fall out. The teeth are triangularly shaped with serrations on the edges.
Tiger Shark
The Tiger shark is a relatively common resident along our east coast. It has a short, blunt snout, long upper labial furrows, and a big mouth with large, saw-edged, cockscomb-shaped teeth and spiracles present. The Tiger shark has a dark grey color with vertical tiger-stripe markings that can fade or be obsolete in adults. Its average size is about 400cm to 650cm with a maximum length of about 800cm. This species lives worldwide in coastal and pelagic waters ranging from the surface to a depth of 140m (up to 350m). It has a wide tolerance for different marine habitats, but seems to prefer turbid waters, occurring on or adjacent to the continental and insular shelves. It is often found in river estuaries, close inshore and in coral atolls and lagoons. Tiger sharks are nocturnal and show cycles of inshore movement at night and retreat to deeper water during daytime. Tiger sharks are mainly solitary creatures.
They feed on fishes, sharks, turtles, birds, invertebrates and even garbage. Such a wide spectrum has often been interpreted as being an unspecialized feeder. However this could reflect a highly specialized adaptation to their biology. Tiger sharks are one of the largest sharks of all and need a lot of food. Their uniquely shaped teeth are highly evolved and therefore allow them to feed on different food items, preventing potential food shortages that could arise with selective feeding. As it has such a large variety of food it might be considered potentially dangerous to humans although it is more likely to feed on humans already dead from other causes.
Reproduction is ovoviviparous (live birth) with between 10 and 80 pups per litter, during summer. The size of pups at birth is between 50cm and 75cm. The pups are very slender and look different than the adults, different markings are present too. This large omnivorous shark is common world-wide in tropical and warm-temperate coastal waters. It is a relatively fast growing and fecund species, and caught regularly in target and non-target fisheries. There is evidence of declines for several populations where they have been heavily fished. Continued demand, especially for the valuable fins, may result in further declines in the future but this species can withstand a higher level of fishing activity than many other species of shark. Additionally, juvenile survivorship increases where adult tiger shark populations have been depleted by fisheries and predation of young is lessened.
QUESTIONS:
1. After reading about both the great white shark and tiger shark, why do you think these two species are so aggressive?
2. What are some other names of great white sharks?
3. What is the name of the organ used to sense vibrations and electrical fields in the water?
4. Describe the water conditions that great white sharks prefer.
5. Name some evidence that shows that great whites are social.
6. Describe some characteristics of the tiger shark.
7. Explain some adaptations of the tiger sharks.
8. Why are some populations of tiger sharks decreasing?
9. Describe the reproduction of the tiger shark.
10. Look at the figure below, and think back to our evolution unit. How do you think natural selection allowed for the drastic changes in tail shape? How do you think each tail allows each shark to be successful in its environment?