Nicknames can either be awesome or embarrassing. In the best-case scenario, they reflect how cool someone thinks you are, and in the worse case, you're stuck being identified by a bad habit or a weird identifying feature.
The Galeocerdo cuvier, a shark identified by biologists in 1822, has a pretty cool nickname most of the time -- tiger shark. Tiger sharks got the moniker from the dark spots and stripes that cover the bodies of juveniles of this species, but the term also embodies all the ferocity that you would expect from a shark that ranks as the second deadliest shark after the great white [source: National Geographic].
To reinforce this point, tiger sharks are also part of a family Carcharhinidae, a family also known as requiem sharks. While "requin" is the French word for shark, the word likely derived from the requiems (or masses for the dead) that were held for men who came upon the more ferocious members of this family.
Despite all that violent glory, the tiger shark has become saddled with a more dubious nickname: "garbage can of the sea." It turns out the tiger shark will eat just about anything, from the sea turtles and seals that make up the main part of its diet, to more exotic items like rubber tires, beer bottles, nails, driver's licenses, explosives, clothes, a crocodile head, cats, pigs and a chicken coop with all its inhabitants [source: Martin]. In Australia, one tiger shark was found with an entire intact horse's head in its stomach [source: Tennesen].
So who are these deadly and hungry sharks? In this article, we'll take a closer look at Galeocerdo cuvier. A quick note before we begin that we'll be looking at the tiger shark, and not the similarly named sand tiger shark. But if you want maximum danger and an exotic diet, you've come to the right place. On the next page, we'll find out how to identify a tiger shark and learn about the anatomical features that differentiate them from other sharks.
Tiger Shark Teeth and Anatomy
How will you know when a tiger shark is swimming toward you? As we mentioned, tiger sharks get their name from the tiger-like stripes and spots that are most prevalent on juveniles. The sharks are bluish-green to dark gray on top, with a yellowish or white underbelly [source: Knickle].
When they're born, tiger sharks measure only 20 inches to 30 inches in length (51 centimeters to 76 centimeters) [source: MarineBio]. But they get much bigger: The full-grown tiger shark reaches 10 feet to 14 feet in length (3 meters to 4 meters) and weighs between 850 pounds and 1,400 pounds (385 kilograms and 635 kilograms) [source: National Geographic]. Larger tiger sharks can reach 17 feet (5 m) and 2,000 pounds (907 kg) [source: Knickle]. While not the biggest fish in the sea -- for comparison, the largest shark, the whale, tips the scales at 75,000 pounds (34,019 kg) and measures 65 feet (20 m) [source: MarineBio] -- the tiger shark does rank near the top of the list.
Tiger sharks are generally considered slow and sluggish, but their fins are capable of fast bursts of energy when they're tracking prey. Like other sharks, the tiger shark moves with its fins. The main factors in mobility are the pectoral fin and the caudal fin, or the tail. The dorsal fins on top help the tiger shark change directions. Like other shark species, they also have vibration detectors along their sides that help them to detect movement in the water. Tiger sharks have very thick hides, once described by a scientist as six to 10 times the strength of an ox hide [source: Tennesen].
The tiger shark has a wide mouth compared to other sharks in its family, and inside the tiger shark's blunt snout is something that really sets it apart: its teeth. Each tooth is almost like having several teeth in one space; the sharp, primary cusp extends down, ready to tear into prey. Along the primary cusp, or point, are tiny little serrated cusplets that can saw into the food. The tiger shark has identical upper and lower jaws, and with all these serrated teeth, there's really nothing that the tiger shark can't eat. Even the tough shells of sea turtles are no match for the tiger shark.
Where does the tiger shark live, and what does it do all day? We'll take a look on the next page.
Tiger Shark Habits and Habitat
The tiger shark loves warm waters and is found in most tropical and temperate regions. Other than a ready supply of food, tiger sharks don't have a lot of other requirements for their abode. Tiger sharks are found both on the surface and in depths of up to 1,150 feet (350 meters) [source: Knickle] and they're found in lots of different waters, including river estuaries and harbors. Most often, though, this shark is found in murky waters in coastal areas. These areas yield a large number of things to eat, and as you might have picked up, the tiger shark likes to eat.
The tiger shark will travel a long way for a bite to eat; one study found that the tiger shark swam about 30 miles to 40 miles (48 km to 64 km) a day looking for food [source: Tennesen]. It also doesn't appear that tiger sharks have a pattern of particular feeding places. Rather, the sharks seem to visit sites on a somewhat irregular basis, returning to feeding sites anywhere from every two weeks to every 10 months [source: Tennesen].
It's sometimes hard for biologists to separate the tiger shark's love of food from other factors when it comes to location. For example, it's largely believed that tiger sharks migrate to warmer locations when it gets cold, but biologists aren't sure if the tiger sharks are following their prey, or if they just prefer a warmer climate [source: Heithaus]. The tiger shark is generally thought to be a nocturnal animal, but in some cases, it's been spotted feeding during the day. In Hawaii for instance, tiger sharks are not nocturnal because they frequently eat monk seals, which are diurnal.
Tiger sharks are primarily solitary hunters, and you may only see a group of these sharks when there's a large amount of food nearby. And while tiger sharks spend a lot of time eating and looking for food, at some point, they have to make other tiger sharks. Tiger sharks are ovoviviparous, which means that shark eggs are fertilized and carried within the mother, as opposed to animals that lay eggs that hatch outside.
When tiger sharks mate, the male usually bites the female on her back and fins to hold her in place. When females have been examined in the wild, scientists usually find the remnants of this mating ritual in the extensive scarring on the female's back. Females only bear young about once every three years, perhaps because of the significant pain associated with breeding.
Females then carry for a term of 14 to 16 months [source: Knickle]. Although the average litter size is around 40, tiger sharks can give birth to anywhere from 10 to 80 pups [source: Ritter]. Once born, however, a tiger shark is on its own, even though it's fairly tiny and grows slowly. Juvenile tiger sharks have an elongated tail which makes it difficult to swim very fast. The tiger markings that are typical of younger tiger sharks may be a way to blend in with the waves near the coast, so that larger predators don't find them.
Baby tiger sharks better watch out -- larger tiger sharks have been known to eat them! Read on to find out all the other zany things that tiger sharks eat.
Tiger Shark Prey and Predators
As we've mentioned, one of the most interesting things about tiger sharks is its diet. The tiger shark's diet changes as it ages. Small tiger sharks feast primarily on fish and sea snakes, but as they grow, their giant mouths and increased size allow them to catch larger prey. Studies have shown that the tiger shark has a very adaptable palate; in Hawaii, tiger sharks feast most commonly on sea birds, but in Australia, sea snakes are usually on the menu [source: Heithaus].
For the most part, tiger sharks feed on local marine species. One study that evaluated the contents of tiger sharks' stomachs found that dugongs, a mammal similar to the manatee, were present about 47 percent of the time. Sea snakes were found 60 percent of the time, and sea turtles were found in 27 percent of the sharks, although only in larger sharks [source: Heithaus].
But what gets people's attention is the wackier things that have shown up in a tiger shark's stomach. Rubber boots, bags of charcoal, boat cushions, hubcaps, pets, raincoats, handbags, cow's hooves, deer antlers, lobsters, a suit of armor, sneakers with legs attached…this list could go on for a while [source: McRae]. Scientists are still determining whether such a diet means that the tiger shark is primitive and unevolved in its willingness to eat anything, or whether being able to eat anything is a smart evolutionary defense [sources: MarineBio, Ritter].
Because tiger sharks live in warm waters, they're likely to make human contact, and sometimes people become the prey of the tiger shark. Because the tiger shark's appetite is so voracious, it's also less likely that they'll just try a nibble and retreat, as some other sharks do. According to the International Shark Attack File, the tiger shark has been responsible for 155 attacks on people since 1580, far behind the great white's 437 and edging out the bull shark's 110 [source: International Shark Attack File]. Together, these three sharks are responsible for 99 percent of attacks on humans, but these numbers shouldn't necessarily keep you out of the water. In Hawaii, for example, the odds of being attacked by a shark are about one in 5 million [source: Tennesen].
Tiger sharks have also been known to eat other tiger sharks, but they're not the only ones -- a tiger shark's fins are a hot culinary commodity in Asian culture. Shark fins provide the spaghetti-like noodles in shark-fin soup. In Hong Kong, a tureen of shark-fin soup costs $100 [source: McRae]. Fishermen eager to cash in on the high price of shark fins sometimes amputate the fins of sharks and then release them, which is a death sentence because definned sharks cannot swim fast enough to catch their prey.
Tiger sharks also are harvested for their flesh, which can be used to make leather, and for their livers, which have high levels of vitamin A and can be used to make vitamin oils. Tiger sharks are also among the sharks caught for sport by fishermen, and sometimes the government has sponsored the fishing of tiger sharks. In Hawaii in the late 1950s, after a spate of tiger shark attacks, a state-sponsored program provided $300,000 to rid the waters of tigers. As we learned in the last section, this might not be an effective way to catch the offending animal because tiger sharks don't usually stay in the same place for long. Because of these human threats -- tiger sharks have no other predators in the sea -- tiger sharks are listed as a near-threatened species by the World Conservation Union.
However, not everyone is out to get the tiger sharks. Scientists say that predators such as the tiger shark keep the ocean's ecosystem in balance, and in Native Hawaiian belief, tiger sharks are aumakua, or sacred guardian spirits.
If you'd like to learn more about tiger sharks, swim over to the links on the next page.
We may be fascinated by sharks, but they can cause trouble for other species. Learn what Earth would be like if there were no sharks at HowStuffWorks.
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More Great Links
- "Dugong." National Geographic. (April 18, 2008)http://animals.nationalgeographic.com/animals/mammals/dugong.html
- "Galeocerdo cuvier, Tiger Shark." MarineBio.org. (April 15, 2008)http://marinebio.org/species.asp?id=37
- Heithaus, Michael R. "The biology of tiger sharks, Galeocerdo cuvier, in Shark Bay, Western Australia: sex ratio, size distribution, diet, and seasonal changes in catch rates." Environmental Biology of Fishes. 2001. (April 15, 2008)http://www.monkeymiadolphins.org/Pdf/Heithaus%202001.pdf
- "Is there a difference between tiger sharks and sand tiger sharks?" North Carolina Aquariums. (April 15, 2008)http://www.ncaquariums.com/askaquarium/tigers.htm
- "ISAF Statistics on Attacking Species of Shark." International Shark Attack File. Updated Jan. 29, 2008. (April 15, 2008)http://www.flmnh.ufl.edu/fish/sharks/Statistics/species2.htm
- Knickle, Craig. "Tiger Shark." Florida Museum of Natural History Ichthyology Department. (April 15, 2008)http://www.flmnh.ufl.edu/fish/Gallery/Descript/Tigershark/tigershark.htm
- Martin, R. Aidan. "Tiger Shark." ReefQuest Centre for Shark Research. (April 15, 2008)http://www.elasmo-research.org/education/ecology/coral-tiger.htm
- McCarthy, Terry. "Why Can't We Be Friends?" Time. 2001. (April 15, 2008)http://www.time.com/time/2001/sharks/cover.html
- McRae, Michael. "Misunderstood Predator." Equinox. September/October 1992. (April 15, 2008)
- "Requin." The Free Dictionary. (April 15, 2008)http://www.thefreedictionary.com/Requin
- "Rhincodon typus, Whale Shark." MarineBio.org. (April 18, 2008)http://marinebio.org/species.asp?id=47
- Ritter, Erich K. "Fact Sheet: Tiger Sharks." Shark Info. 1999. (April 15, 2008)http://www.sharkinfo.ch/SI4_99e/gcuvier.html
- Tennesen, Michael. "A Killer Gets Some Respect." National Wildlife. August/September 2000. (April 15, 2008)http://www.nwf.org/nationalwildlife/article.cfm?articleId=293&issueId=31
- "Tiger Shark." National Geographic. (April 15, 2008)http://animals.nationalgeographic.com/animals/fish/tiger-shark.html
- "Tiger Shark FAQ's." Sharklife Conservation Group. (April 18, 2008)http://www.sharklife.co.za/index.asp?Content=134
- Whitney, Nicholas M. and Gerald L. Crow. "Reproductive biology of the tiger shark (Galeocerdo cuvier) in Hawaii." Marine Biology. Sept. 26, 2006. (April 15, 2008)
- Wirsing, Aaron J., Michael R. Heithaus, Lawrence M. Dill. "Tiger shark (Galeocerdo cuvier) abundance and growth in a subtropical embayment: evidence from 7 years of standardized fishing effort." Marine Biology. Feb. 25, 2006.