Negaprion

Diversity

The genus Negaprion is one of 12 genera in the family Carcharhinidae, commonly known as requiem sharks. The genus contains two extant species: the lemon shark, Negaprion brevirostris, and the sicklefin lemon shark, Negaprion acutidens. The genus also includes one extinct species, Negaprion eurybathrodon. Species in this genus inhabit coastal water in the Atlantic, Pacific, and Indian Oceans and. They can measure between 150 and 300 cm and weigh up to 180 kg, and use their grayish yellow coloring to blend in to the sandy ocean floor (Morgan 2018). Lemon sharks are apex predators, but they are regularly hunted for their fins and are now listed as vulnerable on the IUCN Red List. (Morgan, 2018)

Geographic Range

Negaprion species inhabit tropical temperate regions around the world. The common lemon shark (N. brevirostris) is found in the nearctic and neotropical regions of the Atlantic Ocean, from the northern coast of the United States all the way to southern Brazil, including the Caribbean and the Gulf of Mexico. There is a relict population of N. brevirostris in the eastern Pacific along the coast of Central America (Morgan, 2018). In this population, there is evidence of allopatric speciation corresponding with the formation of the Panama land bridge (Schultz, 2008). The sicklefin lemon shark (N. acutidens) is found in the Indian Ocean along the eastern coast of Africa, around the Sinai Peninsula, and throughout the Indonesian Archipelago to Australia. g. Negaprion species were previously common throughout the tropical and subtropical Indo-West Pacific, but overfishing and habitat destruction has led to their disappearance from the coasts of India and Thailand. (Morgan, 2018; Schultz, 2008)

Habitat

Negaprion species inhabit coastal waters to depths no greater than 200m, though most individuals remain within 50m of the shoreline and often swim so close to the shore that their dorsal fins are exposed above the water. These sharks commonly inhabit mangroves, enclosed bays, and atolls, which also serve as popular nurseries (Filmalter, Dagorn, and Cowley, 2013). Juvenile lemons sharks have strong site attachment, establishing home ranges at birth and rarely traveling more than 20km away from their birthplace. Once mature, lemon sharks engage in migratory behavior, traveling along coastlines for thousands of kilometers. (Filmalter, et al., 2013; Gruber, et al., 1988; Morissey and Gruber, 1993)

Physical Description

Species in the genus Negaprion are characterized by their yellowish coloration, from which they derive the name lemon shark. This coloration can range from olive gray to lighter yellow-brown, with the lightest coloration on the undersides, and they lack conspicuous markings (Morgan 2018). Lemon sharks range from 150 to 300 cm in length, with two prominent dorsal fins - the posterior fin being only slightly shorter in length than the anterior fin. Lemon sharks also have paired pectoral and pelvic fins, small anal fins, and large caudal fins approximately one-fourth their total length (Yoshino 1981). They have broad heads with short snouts, and wide mouths with smooth-edged, single-cusped teeth. The genus is sexually dimorphic, with females smaller on average than males. (Compagno, 2016; Morgan, 2018; Sundström, 2015; Yoshino, et al., 1981)

  • Sexual Dimorphism
  • male larger

Development

Maturity is reached at 225cm for males and 235cm for females, or around 13 years of age. Lemon sharks measure between 55 and 60 centimeters at birth and grow at a rate of approximately four centimeters per month (Gruber, 1981). Some studies have recorded much faster growth rates. This is likely because captive individuals have four times faster growth rates than those in the wild, meaning that food availability is a limiting factor. (Stevens, 1984; Sundström, 2015)

Reproduction

Information about shark breeding behavior is very limited, but it is known that they exhibit internal fertilization. Males have paired claspers used for sperm transfer by attaching to the female. The mating process involves males grasping onto females with their teeth, causing females to often exhibit lacerations during mating season (Feldheim, Gruber, and Ashley, 2002). Females can mate with several males in one mating season and also may store sperm from several males which results in multiple paternity of the litters. (Feldheim, et al., 2002; Feldhiem, et al., 2001)

Lemon sharks are viviparous, giving birth to between 4 and 17 live young in each litter. Females reach sexual maturity between 12 and 16 years of age and then follow a two-year reproductive cycle. Mating usually occurs in spring, with gestation lasting between 10 and 12 months. Females exhibit strong site fidelity for parturition, and their young maintain this strong attachment for several years after their birth. (Feldheim, et al., 2002; Filmalter, et al., 2013; Gruber, et al., 1988)

  • Parental Investment
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
  • pre-hatching/birth
    • provisioning
    • protecting

Lifespan/Longevity

Lemon sharks can live up to 25 years in captivity. There have been no ongoing studies of lifespan in the wild. Negaprion species are estimated to live between 27 and 30 years based on growth rate information ("Lemon Shark", 2018)

Behavior

Lemon sharks are usually solitary but can found in groups of up to 20 individuals, often around fishing docks or protected atolls. These sharks are active throughout the day but are most active around dusk and dawn. Juvenile Negaprion species remain in the nursery areas until they are mature enough to begin their migrations. Little is known about the patterns or distances of these movements, but females will return to the same areas biannually to give birth to their young. ("Lemon Shark", 2018; Morgan, 2018; Sundström, 2015)

Communication and Perception

Lemon sharks use a number of sensory channels to communicate. Like all sharks, Negaprion species have specialized receptors on their snouts called Ampullae of Lorenzini, which can detect weak electrical fields. This adaptation allows them to detect the electrical currents given off by prey, as well as by salts in blood which allows them to locate potential prey. The Ampullae can also detect mount changes in water temperature and salinity. Lemon Sharks also have a homing sense which enables females to return to the same areas each year in order to give birth. (Fields, 2007; Murray, 1961)

These sharks can orient themselves based on sound at a distance of about two meters, which is less than most large sharks.They can hear low frequencies best, with a low threshold of 40 hertz, but are also receptive to higher frequencies up to 320 Hertz. (Nelson, 1967)

Smell plays an important role for lemon sharks in food localization, predator detection, homing and navigation, and also likely in mating. It enables them to detect chemical cues at great distances because those cues can be transported on currents much farther than electric signals. (Tricia and Kajiura, 2010)

Lemon sharks have laterally mounted eyes with little overlap between their monocular fields of vision. They have vertically slit pupils which contract under bright light, and retinas with cones which allow them to see in color. (Hueter and Gruber, 1982)

Food Habits

Young feed mostly on teleost fishes, crustaceans, and octopods. Older sharks eat mostly teleosts and cartilaginous fishes (other sharks), and sometimes even seabirds. Lemon sharks use sight, smell, hearing, and electrical sensitivity in order to locate food. (Fields, 2007; Stevens, 1984)

Predation

Adult lemon sharks have no predators. Juvenile sharks are occasionally eaten by adults or by other shark species. (Sundström, 2015)

Ecosystem Roles

Lemon sharks are hosts to a variety of endo- and ectoparasites, including copepod species and tapeworms. Remoras (Echeneis naucrates) are also commonly found on lemon sharks, though these two organisms share a symbiotic relationship. Remoras latch onto sharks for transportation and eat scraps from their meals. In return, Remoras eat dead skin and dermal parasites, keeping the sharks healthy.

Lemon sharks are apex predators, eating most smaller fish and crustaceans that are present in their habitats. (Fields, 2007; "Lemon Shark", 2018)

Mutualist Species
  • Echenesis nucrates

Economic Importance for Humans: Positive

Historically, many parts of the lemon shark were used and sold, including the hide for leather and the liver which was used to produce liver oil with a high vitamin content. The flesh was sometimes used for fertilizer or chicken feed, or dried for human consumption (Baughman and Springer, 1950). More recently, Negaprion are hunted for their use in shark fin soup, a highly profitable practice. (Baughman and Springer, 1950; Sundström, 2015)

Due to its relative abundance in coastal water, its adaptability to laboratory conditions, and their phyletic position, sharks in the genus Negaprion are some of the most commonly studied sharks (Hueter and Gruber, 1982). They are well suited for experimental conditions because of their ability to ventilate their gills while stationary, which is an unusual trait among sharks.

Lemon sharks are also often used in aquariums because of their size and physical appearance. (Hueter and Gruber, 1982; Sundström, 2015)

  • Positive Impacts
  • food
  • body parts are source of valuable material
  • research and education
  • produces fertilizer

Economic Importance for Humans: Negative

Lemon sharks pose a very minimal threat to humans. There have been only 10 reports of unprovoked lemon shark attacks, none of which were fatal. (Sundström, 2015)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

There are currently no conservation measures in place for any Negaprion species. Lemon sharks from the Atlantic and Pacific Oceans are listed as near threatened on the IUCN Red List. Sicklefin lemon sharks from the Indian Ocean is listed as vulnerable due to overfishing and habitat loss and isolation. Sicklefin lemon sharks are popular in shark fin soups and are occasionally still caught for meat. Their population is declining, but no conservation efforts have been initiated yet. (Sundström, 2015)

  • IUCN Red List [Link]
    Not Evaluated

Contributors

Elena Haverluk (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Arctic Ocean

the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

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Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

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acoustic

uses sound to communicate

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

crepuscular

active at dawn and dusk

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

electric

uses electric signals to communicate

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

internal fertilization

fertilization takes place within the female's body

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

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