Hammerhead Shark


Hammerhead_Shark_2.jpg
This interesting animal is named after the unique "hammer-like" shape of its head. Photograph by Brian J. Skerry

Kingdom: AnimaliaPhylum: ChordataClass: ChondrichthyesOrder: CarcharhiniformesFamily: SphyrnidaeGenus: Sphyrna [1]
Characteristics

Length: 3 – 20 ft
Weight: 500 - 1000 lbs
Hammerhead_to_Human.gif
A Hammerhead Shark in relation to a 6-ft human
Schools: 200 - 500
Speed: 15 mph
Lifespan: 20 - 30 years [2]
Uniquely "Hammer" Shaped Head

Diet

Hammerheads have a wide variety of species on which they prey including crustaceans and invertebrates such as Herring, Mackerels, Sardine, Cra, Octopuses, Squid, Stingray, and Smaller sharks. [3]

Unique Shape of Head

The unique shape of the hammerhead shark's head is said to be an aid in hunting other animals. The unique shape is a result of evolutionary survival. They have a 360 degrees vertical vision. This helps the shark see above and below it all times. The hammerhead doesn't rely on speed to catch its prey as a great white catches a tuna; rather, the hammerhead relies on its vision to spot out a hidden stingray underneath sand on the bottom floor. The Sphyrna species also uses its head to pin down and paralyze its prey before eating it.The unique shape of this amazing shark's head is used for other purposes such as aiding the shark in turning. It is also used as a "wing" that helps keep the shark afloat because if they stop swimming, they drown. [4]
Location


The Hammerhead Shark is generally found in warmer tropical waters. They can be found on continental shelves and coastlines. [5]
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The shaded area is where hammerhead sharks generally reside. Hammerheads live just north and south of the equator where the waters are warmer.


Species

There are 9 known species of Sphyrna. The different species of hammerheads received there names in relation to different characteristics they are attributed to. Some of these various characteristics are viewed as evolutionary advantages that these sharks have developed over time.
—Winghead Shark - Remarkably wide lobes on its head. Small and harmless.—Scalloped Bonnethead - Smallest species of hammerhead.—Whitefin Hammerhead - Prominent indentations in middle and side of head.—Scalloped Hammerhead - Most commonly though of hammerhead.—Scoophead - This is similar to scalloped bonnethead, but is distinguished by broadly arched mouth and shorter snout.—Great Hammerhead - Largest species of hammerhead (about 20 feet). Sickle-shaped dorsal-fin.—Bonnethead - Only shark to display sexual dimorphism, or when female and male adults look different in appearance from each other.—Smalleye Hammerhead - Likes muddy areas with poor visability. —Smooth Hammerhead - The second largest hammerhead. Called the smooth hammerhead because distinctive head is flattened and laterally extended. [6]

Traveling in Schools

The scalloped hammerhead has been known to travel in massive schools at times. These schools of sharks range anywhere from 200 - 500. Sharks are not known to travel in schools so this catches the attention of many researchers. It is said that hammerhead sharks have a highly developed brain and as a result have an inclination towards being social. These hammerheads migrate according to the magnetic field coming from under the earth. [7]

Reproduction

Hammerhead Sharks usually reproduce about one to two times per year. The reproduction occurs as a result of the male shark violently biting the female until she agrees to reproduce. These bites can leave gaping wounds on the female shark that can become infected but are usually cleaned by fish who feed off the bacteria. You can usually tell a female hammerhead apart from a male because females retain scars from these bites. It has been studied that some males have also received these bite marks.The hammerheads give live birth. They sometimes end up eating their own young. An average litter size for the hammerhead is anywhere from 15 to 30 pups. The young hammerheads are immediately independent. [8]


There was a case in 2007 in which an isolated female hammerhead was thought to asexually reproduce. Scientists thought it was asexual reproduction because this shark had been captive and separated from the wild for about three years. The claims were eventually concluded to be false because it is understood that the female hammerhead can store sperm in its body for an extended period of time. [9]
hammerhead3.jpgEndangered

Hammerhead Sharks were recently added to the endangered spieces list due to over fishing and demand for fins. (In Asian cultures "Shark Fin Soup" is a delicacy) [10]








References


1. http://a-z-animals.com/animals/hammerhead-shark/ Updated 2011. Visited 11-26-2011.
2. "Hammerhead Shark Shpyrna" http://animals.nationalgeographic.com/animals/fish/hammerhead-shark/#. Updated 2011. Visited 11-26-2011.
3. http://a-z-animals.com/animals/hammerhead-shark/ Updated 2011. Visited 11-26-2011.
4. American Physiological Society, Donna Krupa. "Why the hammerhead shark's head is in the shape it's in". http://www.light-science.com/hammerhead.html Updated 2011. Visited 11-27-2011.
5. http://a-z-animals.com/animals/hammerhead-shark/ Updated 2011. Visited 11-26-2011.
6. http://en.wikipedia.org/wiki/Hammerhead_shark#Species
7. Alessandro De Maddalena, Alex Buttigieg. "The Social Lives of Hammerheads - worldandi.com". June 2006. http://www.worldandi.com/subscribers/feature_detail.asp?num=25044
Updated 2011. Visited 11-26-2011
8. http://www.sharks-world.com/hammerhead_shark.html
9. Stephen Edwards. "Hammerhead Sharks Reproduce Asexually - wired.com". 23 May 2007. http://www.wired.com/wiredscience/2007/05/hammerhead_shar/ Updated 2010. Visited 11-28-2011
10. Jennifer Viegas. "Shark Fins Traced To Endangered Populations". 1 Dec. 2009. http://news.discovery.com/animals/endangered-hammerhead-sharks-finning.html Updated 2011. Last Visited 11-29-2011


Figure G1 http://images.nationalgeographic.com/wpf/media-live/photos/000/005/cache/hammerhead-shark_568_600x450.jpg
Figure G2 http://animals.nationalgeographic.com/animals/fish/hammerhead-shark/#
Figure G3 http://animals.nationalgeographic.com/animals/fish/hammerhead-shark/
Figure G4 http://www.youtube.com/watch?v=DwyPU7BYl5E&feature=related
Figure G5 http://www.sharknames.net/wp-content/uploads/2011/04/hammerhead-shark-300x201.jpg