Lemon shark

Lemon shark

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The lemon shark, Negaprion brevirostris, is a shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

 in the family Carcharhinidae, that can grow to 10 feet (3 m) long. It is known as the lemon shark because, at certain depths, light interacting with the local seawater can give this shark a tanned and yellow pitted appearance, much like the surface of a lemon.

Description


This stocky, powerful shark is named for its pale yellow-brown to grey skin, which lacks any distinctive markings. This provides perfect camouflage when swimming over the sandy seafloor in its coastal habitat. It has a flattened head with a short, broad snout, and the second dorsal fin is almost as large as the first.

Distribution and habitat


The lemon shark is found mainly along the subtropical and tropical parts of the Atlantic and Pacific coasts of North and South America, and around Pacific islands
Pacific Islands
The Pacific Islands comprise 20,000 to 30,000 islands in the Pacific Ocean. The islands are also sometimes collectively called Oceania, although Oceania is sometimes defined as also including Australasia and the Malay Archipelago....

. The longest lemon shark recorded was 13 ft (4 m) long, but they are usually 8–10 ft (2.4–3 m). They like tropical water, and like to stay at moderate depths. They are often accompanied by remora
Remora
The remora , sometimes called a suckerfish or sharksucker, is an elongated, brown fish in the order Perciformes and family Echeneidae...

s.

Reproduction


Lemon sharks are viviparous, females giving birth to between 4 and 17 young every other year in warm and shallow lagoons. The young have to fend for themselves from birth, and remain in shallow water near mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...

s until they grow larger. With increasing size they venture further away from their birthplace. At maturity, at a size of 1.5–2 m and an age of 12–15 years, they leave shallow water and move into deeper waters offshore. However, little is known of this life stage. Maximum recorded length and weight is 340 cm and 183 kg.

Recent work in genetics by Kevin Feldheim and Samuel Gruber may suggest that adult sharks travel hundreds of kilometers to mate. Another possibility is that populations far apart may have been separated in recent times. Further research in this area in needed for an understanding of the lemon shark's breeding behavior and ecology.

Importance to humans



Lemon sharks are a popular choice for study by scientists as they survive well in captivity, unlike many other species such as the great white
Great white shark
The great white shark, scientific name Carcharodon carcharias, also known as the great white, white pointer, white shark, or white death, is a large lamniform shark found in coastal surface waters in all major oceans. It is known for its size, with the largest individuals known to have approached...

, which die in captivity because of food refusal. The species is the best known of all sharks in terms of behavior and ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

, mainly because of the work of Samuel Gruber at the University of Miami
University of Miami
The University of Miami is a private, non-sectarian university founded in 1925 with its main campus in Coral Gables, Florida, a medical campus in Miami city proper at Civic Center, and an oceanographic research facility on Virginia Key., the university currently enrolls 15,629 students in 12...

, who has been studying the lemon shark both in the field and in the laboratory since 1967. The population around the Bimini Islands in the western Bahamas, where Gruber's Bimini Biological Field Station is situated, is probably the best known of all shark populations. As of 2007, this population is experiencing a severe decline and may disappear altogether as a result of destruction of the mangroves for construction of a golf resort. There have been 22 known lemon shark attacks since 1580, but no deaths.

Electroreceptors


All sharks have electroreceptors concentrated in their heads, called the ampullae of Lorenzini
Ampullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...

. These receptors detect electrical pulses emitted by potential prey. Lemon sharks are bottom dwellers. They have very poor eyesight and cannot see well to find their food, but are equipped with extremely sensitive and accurate magnetic sensors in the nose.

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