Negaprion brevirostris
(full classification below)

The lemon shark, so named for its brownish-yellow colouring on its dorsal side (the ventral side is an off-white colour), is a subtropical shark valued by scientists for being easy to find and study. Lemon sharks can be found in warm waters, usually somewhere between the surface and 92 metres deep, on continental and insular shelves in the Pacific and Atlantic oceans. In the eastern Pacific, the sharks can be found from as far north as the coastline of Baja California and the Gulf of California in Mexico to as far south as Ecuador. In the western Pacific, lemon sharks can be found off the coast of Australia. In the western Atlantic Ocean, lemon sharks can be found along the eastern coast of the United States, in the Gulf of Mexico, the Caribbean, and off the eastern coast of Brazil. Lemon sharks are also native to the eastern Atlantic Ocean, near the African countries of Senegal and Cote d'Ivoire. Lemon sharks can tolerate a wide range of saline levels and have even been known to enter freshwater at times. Lemon sharks typically aren't found in the open ocean but are believed to travel that far out for migration.

Lemon sharks have been known to travel alone, in pairs, and groups. The sharks can, if necessary, swim at speeds recorded up to 20 miles per hour for brief periods of time, making them one of the fastest sharks on record. Normally, lemon sharks swim 0.3 to 0.4 body lengths per second (e.g., it takes a lemon shark about two and a half to three seconds to swim a distance equivalent to the length of its body). Unlike many species of shark, the lemon shark doesn't need to swim constantly to survive (it's not uncommon to spot one lying on a sandy ocean floor during the day). Lemon sharks are believed to return to their birthplace during their migratory swimming. Lemon sharks are frequently tagged by scientists in a procedure which also allows the scientists to remove a small piece of a shark's fin (which heals quickly) for DNA sampling and some of the contents of the shark's stomach. The entire procedure takes about three minutes to complete, after which the shark is returned to the water relatively unharmed.

Adult lemon sharks typically range in length from 2.45 to 3.10 metres (8 to 10 feet) and can weigh up to 183.7 kilograms (about 408 pounds). The fins of the lemon shark are relatively large, compared to those of other sharks. Lemon sharks' first and second dorsal fins are nearly the same size. Lemon shark heads are broad and flat. The snout is short and the fins are without any markings.

Lemon sharks have a nictitating membrane (an inner eyelid) which they usually close when attacking prey to protect their large eyes. Scientists believe, based on a series of experiments over the years, that eyesight plays a more important role than any of the sharks' other senses in hunting. In the early 1960s, for example, scientists temporarily blinded a group of lemon sharks, then released them into a tank with a group of lemon sharks that were still able to see normally. A 113 kilogram chunk of Blue Marlin was placed in the tank. All the sharks which could still see were able to reach the food but the blind sharks were unable to find it at all. Further studies have shown that lemon sharks appear to be attracted to bright objects and leave dull ones alone for the most part.

Lemon sharks have rows of triangular, slightly curved teeth (similar to those of a barracuda), designed to catch more slippery types of fish. When a lemon shark loses a tooth, one from the row behind the lost tooth is able to rotate into the place of the lost tooth. Young lemon sharks lose their entire set of teeth, one at a time, every seven to eight days. Lemon sharks prey primarily on other fish (even members of their own species occasionally, making themselves their only non-human predator) but will also eat crustaceans, mollusks, and rays. Lemon sharks are shy but will become aggressive if provoked. In the past decade, over twenty attacks by lemon sharks have been reported. None of those attacks were fatal. Lemon shark meat may be safely ingested by humans. The fins of lemon sharks may be used to make shark-fin soup. Leather can be crafted from lemon shark hide and the oil from the shark's liver may be used as a source of vitamins.

Lemon shark females reach sexual maturity by the time they're about 2.45 metres in length. The females give birth once every couple of years to a litter of 60-65 centimetre pups. The litter's number may range from only four to seventeen. The young are born live, as opposed to the mothers laying eggs, after a gestation period of approximately a year. Once born, the pups are on their own. The mother lemon shark won't care for her pups and may even try to eat them if they stick around. The young remain in sheltered coastal nurseries until they have grown large enough to survive in more open waters. The young are more active during the day, while the adults tend to be more active during the night. In captivity, lemon sharks have been observed living up to twenty five years of age, and though they live better than many species in captivity, it's thought they live longer in the wild.

Domain: Eucarya
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Chondrichthyes
Subclass: Elasmobranchii
Order: Carcharhiniformes
Family: Carcharhinidae
Genus: Negaprion
Species: brevirostris

Sources:
http://filaman.uni-kiel.de/Summary/SpeciesSummary.cfm?ID=897&genusname=Negaprion&speciesname=brevirostris
http://www.geocities.com/deadliestsharks/lemon.htm
http://members.ozemail.com.au/~bilsons/Sharks3.htm#lemon
http://www.coast-shark.com/coast-shark/ID/Lemon/
http://www.pbs.org/wgbh/nova/sharkattack/tidbits.html
http://www.suite101.com/article.cfm/aquatic_animals/85501

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