Lemon shark
| Lemon shark | ||||||||||||
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A lemon shark |
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| Negaprion brevirostris | ||||||||||||
| ( Poey , 1868) |
The lemon shark ( Negaprion brevirostris ), also known as the Atlantic lemon shark , is a strong shark up to 340 cm long from the genus of lemon sharks . It got its name because of its yellowish color. It lives on the coasts of North , South and Central America as well as on the coast of West Africa .
features
Lemon sharks are yellowish-brown on the upper side (more rarely dark brown to dark gray-brown) and have a light yellow to white belly, which distinguishes them from their relatives, the sickle-fin lemon sharks ( Negaprion acutidens ). The shark's yellowish to olive-green flanks give it its name ; the fins are gray-brown, the anal fin usually yellowish with a gray border.
Its powerful mouth is round and wider than it is long, which means that it is sometimes mistaken for the bull shark . However, this does not have the typical fin formation of lemon sharks , in which both dorsal fins are almost the same size and are relatively far back. The upper jaw has 15 teeth on both sides, the lower jaw 13 to 14, at the front one to three smaller teeth can be found in both jaws.
The animals are strong and grow very large. In the wild they sometimes grow to over 340 cm long. The size of lemon sharks living in captivity is between 240 and 260 cm, with the males being on average 10 cm larger than their female counterparts. The weight of a fully grown lemon shark is around 180 kg. The animals have five gill slits and, as a rule, no injection hole , although this can happen with individual specimens.
Way of life
Lemon sharks are nocturnal and prefer shallow and medium-depth waters of bays , reefs , docks and estuaries , but are also sighted at depths of up to 90 meters. Young animals form small schools and live in the mangrove swamps of the coast to avoid being stalked by their older conspecifics and other predatory fish.
Life expectancy is 15 to 20 years. The oldest known animal was verifiably over 30 years old.
Reproduction
The mating season of lemon sharks takes place in late spring or early summer. As with most shark species, the male dominates, while the female has to endure powerful bites in the fins and tail . After mating, it takes twelve months for the mother to give birth to her 4 to 17, mostly 7 to 10 cubs alive ( viviparia ). Birth mostly takes place in areas of the Bahamas and the Exumas .
The young sharks are between 60 and 70 cm tall and have a yolk sac placenta . Until they can swim independently, they are still connected to their mother by an umbilical cord , after which they are on their own and form small schools. The development with a growth of about 10 cm in the first years and later about 0.5 cm per year takes a very long time, so that sexual maturity is only reached at 12 to 15 years (corresponds to about 240 cm).
Recent genetic studies by Kevin Feldheim, Sonny Gruber and Mary Ashley indicate that adult sharks must migrate several hundred kilometers to mate or, alternatively, populations that are widely separated must have recently separated.
Food and hunting
Lemon sharks hunt any fish of the appropriate size that they can get hold of. They mainly eat red mullets , bones fish, groupers , mackerel , tuna , squids , edible crabs , octopuses , grunts , but also other sharks and rays as well as sea birds. Adult animals usually hunt alone. The senses of smell, hearing and sight are very well developed, which is very helpful when hunting. The teeth in the lower jaw are pointed and are used to hold the prey, while the jagged teeth of the upper jaw cut large pieces of meat from the victim. The teeth are symmetrically arranged and positioned upright in the jaw. During the hunt, lemon sharks often lurk motionless for prey just above the seabed and, thanks to their color, blur against the underground of sand, stones and vegetation.
distribution
The lemon shark lives in the coastal waters of the western and eastern Atlantic and the eastern Pacific from southern Baja California to Ecuador . It is most common in the Caribbean , off Florida, and around the Antilles . He is only an occasional and summer visitor north of Florida. It can also endure freshwater for a short time and is occasionally found in the Amazon Delta area and also a little upstream.
Its closest relative, the sickle-fin lemon shark , inhabits the Red Sea , the Pacific and the Indian Ocean .
Lemon shark and human
Shark attacks
Since lemon sharks get quite large, often hang out in shallow waters, and are easily provocable, they can also be dangerous to humans. It is widely reported that lemon sharks have attacked humans for no apparent cause. Attacks on people are also repeatedly observed in the open sea, although it cannot be ruled out that these were provoked.
Hazard and protection
According to the IUCN Red List of 1994, there is only a low risk of the species becoming extinct . For a long time the fishing industry was not used for lemon sharks, but the species has been caught both commercially and by amateur fishermen for several years. While the fins migrate in shark fin soups, the tough skin is processed into leather. In addition, the chemical pollution of the oceans is very hard on the sharks, and like all predatory fish and whales, heavy metals and toxins such as dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCB) and others accumulate in their tissues.
Research and Captivity
Some scientific experiments were conducted on and with the sharks which found that they were attracted to bright colors like the red and orange of diving suits, life jackets, lifeboats and inflatables. The noise of low-flying helicopters is said to have the same effect . You can also detect low-frequency sound waves generated by people or fish in agony. In the United States, other experiments were made with the sharks, including experiments on cardiac responses, narcotics, eye movements, and adaptation to darkness.
They are easy to keep in captivity and better researched than many other shark species , which is not least due to the work of Prof. Samuel H. Gruber ( University of Miami in Coral Gables ).
The species was even successfully bred in captivity at a marine station in Cape Haze ( Florida ). In doing so, Dr. Eugen Clarke raised several young lemon sharks in a special tank. The experiment ended with a larger male eating the young. One in the Cape Haze Marine Laboratory learned to press a doorbell to get food.
literature
- Kuno Sch. Steuben , Gerhard Krefft: The sharks of the seven seas: species, way of catching and sporty catch. Paul Parey Verlag Hamburg / Berlin 1989, ISBN 3-490-44314-4 .
- The Washington Post , 2005, Aug. 22nd: Scientists Fear Oceans on the Cusp Of a Wave of Marine Extinctions.
- University of South Florida : Feeding Mechanism and Functional Morphology of the Jaws of the Lemon Shark. ( PDF English).
Web links
- Lemon shark pictures
- Informative, structured page about the lemon shark on Hai.ch (German)
- Lemon Shark on Fishbase.org (English)
- Entry on Marinebio.org (English)
- Comprehensive site about the lemon shark (English)
- Negaprion brevirostris in the endangered Red List species the IUCN 2006. Posted by: Gruber & Sundström, 2000. Retrieved on 11 May, 2006.
