Sicklefin lemon shark

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Sicklefin lemon shark
Negaprion acutidens sydney2.jpg
CITES Appendix II (CITES) [2]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Subdivision: Selachimorpha
Order: Carcharhiniformes
Family: Carcharhinidae
Genus: Negaprion
Species:
N. acutidens
Binomial name
Negaprion acutidens
(Rüppell, 1837)
Negaprion acutidens distmap.png
Range of the sicklefin lemon shark
Synonyms

Aprionodon acutidens queenslandicusWhitley, 1939
Carcharias acutidensRüppell, 1837
Carcharias forskalii* Klunzinger, 1871
Carcharias munzingeriKossmann & Räuber, 1877
Eulamia odontaspisFowler, 1908
Hemigaleops fosteriSchultz & Welander, 1953
Mystidens innominatusWhitley, 1944
Negaprion queenslandicusWhitley, 1939
Odontaspis madagascariensisFourmanoir, 1961


* ambiguous synonym

The sicklefin lemon shark (Negaprion acutidens) or sharptooth lemon shark is a species of requiem shark belonging to the family Carcharhinidae, widely distributed in the tropical waters of the Indo-Pacific. It is closely related to the better-known lemon shark (N. brevirostris) of the Americas; the two species are almost identical in appearance, both being stout-bodied sharks with broad heads, two dorsal fins of nearly equal size, and a plain yellow-tinged coloration. As its common name suggests, the sicklefin lemon shark differs from its American counterpart in having more falcate (sickle-shaped) fins. This large species grows up to 3.8 m (12 ft) long. It generally inhabits water less than 92 m (302 ft) deep in a variety of habitats, from mangrove estuaries to coral reefs.

A slow-moving predator feeding mainly on bony fishes, the sicklefin lemon shark seldom travels long distances and many individuals can be found year-round at certain locations. Like other members of its family, this species is viviparous, with females giving birth to no more than 13 pups every other year, following a gestation period of 1011 months. Although they are potentially dangerous to humans and known to respond vigorously to any provocation, under normal circumstances, sicklefin lemon sharks are cautious and tend to retreat if approached. The IUCN has assessed this species as Endangered; its low reproductive productivity and rate of movement limits the capacity of depleted stocks to recover. Off India and Southeast Asia, this species has been severely depleted or extirpated by unregulated exploitation for its meat, fins, and liver oil.

Taxonomy and phylogeny

The sicklefin lemon shark was first described as Carcharias acutidens by German naturalist Eduard Rüppell, in the 1837 Fische des Rothen Meeres (Fishes of the Red Sea). In 1940, Australian ichthyologist Gilbert Percy Whitley moved this species to his newly formed genus Negaprion. The type specimen, designated in 1960, is a 68-cm-long individual caught in the Red Sea off Jeddah, Saudi Arabia. [3] The specific epithet acutidens is derived from the Latin acutus meaning "sharp", and dens meaning "teeth". The sicklefin lemon shark may also be referred to as broadfin shark, Indian lemon shark, Indo-Pacific lemon shark, or simply lemon shark. [2]

Based on microsatellite DNA evidence, the sicklefin lemon shark is thought to have diverged from its sister species N. brevirostris 1014 million years ago, when the closure of the Tethys Sea separated lemon sharks in the Indian Ocean from those in the Atlantic. [4] The ancestral lemon shark species may have been N. eurybathrodon , the fossilized teeth of which occur in both the United States and Pakistan. [4] Morphological and molecular phylogenetic analyses suggest that Negaprion is grouped with the whitetip reef shark (Triaenodon) and the sliteye shark (Loxodon) in occupying an intermediate position on the carcharhinid evolutionary tree, between the most basal genera ( Galeocerdo , Rhizoprionodon , and Scoliodon ) and the most derived ( Carcharhinus and Sphyrna ). [5]

Distribution and habitat

Coral reefs are one of the environments inhabited by the sicklefin lemon shark. Negaprion acutidens tahiti.jpg
Coral reefs are one of the environments inhabited by the sicklefin lemon shark.

The range of the sicklefin lemon shark extends from South Africa to the Red Sea (including Mauritius, the Seychelles, and Madagascar), continuing eastward along the coast of the Indian subcontinent to Southeast Asia, extending as far north as Taiwan and the Philippines, and as far south as New Guinea and northern Australia. This species is also found around numerous Pacific islands, including New Caledonia, Palau, the Marshall Islands, the Solomon Islands, Fiji, Vanuatu, and French Polynesia. [6] [3] This species likely colonized the central Pacific by infrequently "hopping" from one island to the next. Significant levels of genetic differentiation between sicklefin lemon sharks in Australia and French Polynesia, 750 km (470 mi) apart, suggest that little intermingling occurs between regional subpopulations. [4]

An inhabitant of coastal continental and insular shelves, the sicklefin lemon shark occurs from the intertidal zone to a depth of 92 m (302 ft). [7] This species favors still, murky waters and is most common in bays, estuaries, and lagoons, and over sandy flats and outer reefs. Sometimes, an individual may venture into open water; one was filmed in the 1971 documentary Blue Water, White Death, in the vicinity of a sperm whale (Physeter macrocephalus) carcass. Juvenile sicklefin lemon sharks are often found on reef flats or around mangroves, in water so shallow that their dorsal fins are exposed. [3] [8] In Herald Bight off Western Australia, a known nursery, juvenile sicklefin lemon sharks frequent open areas and mangroves in water under 3 m (9.8 ft) deep, but not areas covered by the seagrass Posidonia australis . [9]

Description

Sickle-shaped fins are a distinguishing characteristic of this species. Negaprion acutidens polynesia.jpg
Sickle-shaped fins are a distinguishing characteristic of this species.

The sicklefin lemon shark has a robust, stocky body and a short, broad head. The snout is rounded or almost wedge-shaped, with small nostrils bearing triangular flaps of skin in front. The eyes are small, with no spiracles. Short furrows are present at the corners of the mouth. [3] Thirteen to 16 (usually 14) tooth rows occur on either side of both jaws, not including the tiny teeth at the symphysis (the jaw midline). The upper teeth have a large cusp rising from a broad base, with a notch on each side; these teeth become increasingly angled towards the corners of the mouth. The lower teeth resemble the upper teeth, but are narrower and more erect. [8] The teeth of sharks over 1.4 m (4.6 ft) long are finely serrated. [3]

The fins (especially the dorsal, pectoral, and pelvics) of the sicklefin lemon shark are more falcate (sickle-shaped) than those of the otherwise very similar American lemon shark. The first dorsal fin is positioned closer to the pelvic than the pectoral fins. The second dorsal fin, nearly equal to the first in size, is located over or slightly forward of the anal fin. No ridge is seen between the dorsal fins. The pectoral fins are long and broad, originating below the space between the third and fourth gill slits. The anal fin has a strong notch in the rear margin. The precaudal pit (a cavity just forward of the caudal fin) is oriented longitudinally. [3] The large dermal denticles are overlapping and bear three to five horizontal ridges each. [7] The coloration is a plain yellowish brown or gray above and lighter below, with more yellow on the fins. [10] This species attains a maximum known length of 3.8 m (12 ft), [2] though it typically does not exceed 3.1 m (10 ft). [8]

Biology and ecology

The sicklefin lemon shark usually swims close to the bottom. Negaprion acutidens sydney.jpg
The sicklefin lemon shark usually swims close to the bottom.
Courtship behavior - a male (right) follows a female

A sluggish species, the sicklefin lemon shark is usually seen cruising sedately just above the sea bottom or lying still on it, as unlike most requiem sharks, it is capable of actively pumping water over its gills. However, it will approach the surface in pursuit of food. [3] This shark seldom undertakes long-distance movements. [4] A study at Aldabra Atoll in the Seychelles found, of the tagged sharks that were later recaptured, over 90% were still within 2 km (1.2 mi) of their initial tagging location. [11] Another study at Moorea in French Polynesia found that some of the local sharks were year-round residents of the island, while others were more transitory and visited only occasionally. [12]

Over 90% of the sicklefin lemon shark's diet consists of bottom- and shore-dwelling teleosts, including herring, mullets, mackerel, silversides, needlefish, smelt-whitings, porgies, sea catfish, triggerfish, parrotfish, and porcupinefish. Occasionally, they may also take cephalopods and crustaceans, and older individuals have been known to consume stingrays and guitarfish. [3] [11] [13] [14] This species may be preyed upon by larger sharks. [7] Known parasites include the tapeworms Paraorygmatobothrium arnoldi, [15] Pseudogrillotia spratti, [16] Phoreiobothrium perilocrocodilus, [17] and Platybothrium jondoeorum. [18] Sicklefin lemon sharks have been documented resting on the bottom and eliciting cleanings by bluestreak cleaner wrasses (Labroides dimidiatus), during which they may open their mouths and stop respiring for as long as 150 seconds to give the wrasses access to their mouths and gills. [19]

As with other members of its family, the sicklefin lemon shark is viviparous; the developing embryos are sustained by a placental connection formed from their depleted yolk sacs. Females give birth to one to 13 (usually six to 12) pups every other year in shallow nursery areas, following a gestation period of 1011 months. [3] [11] Unlike in the American lemon shark, scant evidence indicates this species is philopatric (returns to the site of their birth to reproduce). [4] Parturition occurs in October or November at Madagascar and Aldabra, and in January at French Polynesia; ovulation and mating for nonpregnant females takes place at around the same time. The embryos develop a placenta after around four months of gestation, when they still possess vestiges of external gills. The young are born at a length of 45–80 cm (18–31 in). [3] [11] Juvenile sharks grow slowly, at a rate of 12.5–15.5 cm (4.9–6.1 in) per year. Both sexes attain sexual maturity at a length of 2.2–2.4 m (7.2–7.9 ft). [7]

Human interactions

The sicklefin lemon shark is threatened by overfishing. Negaprion acutidens hooked.jpg
The sicklefin lemon shark is threatened by overfishing.

Several apparently unprovoked attacks on humans have been attributed to the sicklefin lemon shark. Due to its formidable size and teeth, it is regarded as potentially dangerous, and certainly this species has been known to defend itself quickly and vigorously if touched, speared, or otherwise provoked or alarmed. Once agitated, this shark can be a persistent adversary; in one case, a shark forced a swimmer to seek refuge atop a coral head, and circled for hours before giving up. However, observations by divers show that normally this shark is shy and hesitant to approach, even when presented with bait. Often, the shark will move away when a diver enters visual range. Young sharks are reportedly more aggressive and inquisitive than the adults. [3] At Moorea, sicklefin lemon sharks are the main attraction of daily shark-feeding ecotourism dives. [12] This shark adapts well to captivity and is displayed in public aquariums. [3]

The IUCN has assessed the sicklefin lemon shark globally as Endangered; it is harvested using anchored and floating gillnets, beach nets, and longlines. [6] The meat is sold fresh or dried and salted for human consumption, the fins used for shark fin soup, and the liver oil is processed for vitamins. [3] The sicklefin lemon shark is highly susceptible to local overfishing, due to its slow reproductive rate and limited movements. Off Southeast Asia, this shark has become scarce under the pressure of expanding, unmonitored, and unregulated fisheries, and has been assessed there as Endangered by the IUCN. Widespread habitat degradation, including pollution and blast fishing on coral reefs and deforestation in mangroves, poses an additional threat to the survival of this species in the region. Already, the sicklefin lemon shark has been extirpated in parts of India and Thailand, and has not been reported from Indonesian markets in recent years despite being historically abundant there. Off Australia, the sicklefin lemon shark is taken in only small numbers intentionally and as bycatch, and has been listed under Least Concern. [6]

Related Research Articles

<span class="mw-page-title-main">Requiem shark</span> Family of sharks

Requiem sharks are sharks of the family Carcharhinidae in the order Carcharhiniformes. They are migratory, live-bearing sharks of warm seas and include such species as the bull shark, lemon shark, spinner shark, blacknose shark, blacktip shark, grey reef shark, blacktip reef shark, silky shark, dusky shark, blue shark, copper shark, oceanic whitetip shark, and whitetip reef shark.

<span class="mw-page-title-main">Grey reef shark</span> Species of shark

The grey reef shark or gray reef shark is a species of requiem shark, in the family Carcharhinidae. One of the most common reef sharks in the Indo-Pacific, it is found as far east as Easter Island and as far west as South Africa. This species is most often seen in shallow water near the drop-offs of coral reefs. It has the typical "reef shark" shape, with a broad, round snout and large eyes. It can be distinguished from similar species by the plain or white-tipped first dorsal fin, the dark tips on the other fins, the broad, black rear margin on the tail fin, and the lack of a ridge between the dorsal fins. Most individuals are less than 1.88 m (6.2 ft) long.

<span class="mw-page-title-main">Blacktip reef shark</span> Species of shark

The blacktip reef shark is a species of requiem shark, in the family Carcharhinidae, which can be easily identified by the prominent black tips on its fins. Among the most abundant sharks inhabiting the tropical coral reefs of the Indian and Pacific Oceans, this species prefers shallow, inshore waters. Its exposed first dorsal fin is a common sight in the region. The blacktip reef shark is usually found over reef ledges and sandy flats, though it has also been known to enter brackish and freshwater environments. It typically attains a length of 1.6 m (5.2 ft). Like other sharks, the females are larger than the males.

<span class="mw-page-title-main">Lemon shark</span> Species of shark

The lemon shark is a species of shark from the family Carcharhinidae and is classified as a Vulnerable species by the International Union for the Conservation of Nature. Lemon sharks can grow to 3.4 metres (11 ft) in length. They are often found in shallow subtropical waters and are known to inhabit and return to specific nursery sites for breeding. Often feeding at night, these sharks use electroreceptors to find their main source of prey, fish. Lemon sharks enjoy the many benefits of group living such as enhanced communication, courtship, predatory behavior, and protection. This species of shark gives birth to live young, and the females are polyandrous and have a biennial reproductive cycle. Lemon sharks are not thought to be a large threat to humans; there have been 10 recorded bites, none of which were life-threatening. The lemon shark's life span is unknown, but the average shark is 25 to 30 years old. The oldest recorded lemon shark in captivity died in 2023 at the age of 40 years.

<span class="mw-page-title-main">Whitetip reef shark</span> Species of shark

The whitetip reef shark is a species of requiem shark, in the family Carcharhinidae, and the only member of its genus. A small shark that does not usually exceed 1.6 m (5.2 ft) in length, this species is easily recognizable by its slender body and short but broad head, as well as tubular skin flaps beside the nostrils, oval eyes with vertical pupils, and white-tipped dorsal and caudal fins. One of the most common sharks found on Indo-Pacific coral reefs, the whitetip reef shark occurs as far west as South Africa and as far east as Central America. It is typically found on or near the bottom in clear water, at a depth of 8–40 m (26–131 ft).

<span class="mw-page-title-main">Ganges shark</span> Species of shark

The Ganges shark is a critically endangered species of requiem shark found in the Ganges River and the Brahmaputra River of India and Bangladesh. It is often confused with the more common bull shark, which also inhabits the Ganges River and is sometimes incorrectly referred to as the Ganges shark. The genus is currently considered to contain three recent species; genetic evidence has shown that both the Borneo river shark and Irrawaddy river shark should be regarded as synonyms of the Ganges shark, expanding the range of the species to Pakistan, Myanmar, Borneo, and Java. While the other members of the genus Glyphis occur in coastal marine waters as well as rivers, the Ganges shark is found only in fresh water, making it the world's only exclusively freshwater shark. The species remains poorly known and very rare.

<span class="mw-page-title-main">Dusky shark</span> Species of shark

The dusky shark is a species of requiem shark, in the family Carcharhinidae, occurring in tropical and warm-temperate continental seas worldwide. A generalist apex predator, the dusky shark can be found from the coast to the outer continental shelf and adjacent pelagic waters, and has been recorded from a depth of 400 m (1,300 ft). Populations migrate seasonally towards the poles in the summer and towards the equator in the winter, traveling hundreds to thousands of kilometers. One of the largest members of its genus, the dusky shark reaches more than 4 m (13 ft) in length and 350 kg (770 lb) in weight. It has a slender, streamlined body and can be identified by its short round snout, long sickle-shaped pectoral fins, ridge between the first and second dorsal fins, and faintly marked fins.

<span class="mw-page-title-main">Horn shark</span> Species of shark

The horn shark is a species of bullhead shark, in the family Heterodontidae. It is endemic to the coastal waters off the western coast of North America, from California to the Gulf of California. Young sharks are segregated spatially from the adults, with the former preferring deeper sandy flats and the latter preferring shallower rocky reefs or algal beds. A small species typically measuring 1 m (3.3 ft) in length, the horn shark can be recognized by a short, blunt head with ridges over its eyes, two high dorsal fins with large spines, and a brown or gray coloration with many small dark spots.

<span class="mw-page-title-main">Silvertip shark</span> Species of shark

The silvertip shark is a large species of requiem shark, in the family Carcharhinidae, with a fragmented distribution throughout the tropical Indian and Pacific Oceans. It is often encountered around offshore islands and coral reefs, and has been known to dive to a depth of 800 m (2,600 ft). The silvertip shark resembles a larger and bulkier grey reef shark, but can be easily identified by the prominent white margins on its fins. It attains a maximum length of 3 m (10 ft).

<span class="mw-page-title-main">Blacknose shark</span> Species of shark

The blacknose shark is a species of requiem shark, belonging to the family Carcharhinidae, common in the tropical and subtropical waters of the western Atlantic Ocean. This species generally inhabits coastal seagrass, sand, or rubble habitats, with adults preferring deeper water than juveniles. A small shark typically measuring 1.3 m (4.3 ft) long, the blacknose has a typical streamlined "requiem shark" shape with a long, rounded snout, large eyes, and a small first dorsal fin. Its common name comes from a characteristic black blotch on the tip of its snout, though this may be indistinct in older individuals.

<span class="mw-page-title-main">Spinner shark</span> Species of shark

The spinner shark is a type of requiem shark, in the family Carcharhinidae, named for the spinning leaps it makes as a part of its feeding strategy. This species occurs in tropical and warm temperate waters worldwide, except for in the eastern Pacific Ocean. It is found from coastal to offshore habitats to a depth of 100 m (330 ft), though it prefers shallow water. The spinner shark resembles a larger version of the blacktip shark, with a slender body, long snout, and black-marked fins. This species can be distinguished from the blacktip shark by the first dorsal fin, which has a different shape and is placed further back, and by the black tip on the anal fin. It attains a maximum length of 3 m (9.8 ft).

<span class="mw-page-title-main">Australian blacktip shark</span> Species of shark

The Australian blacktip shark is a species of requiem shark, in the family Carcharhinidae, endemic to northern and eastern Australia. Favoring the upper and middle parts of the water column, it can be found from the intertidal zone to a depth of 50 m (160 ft). Appearance-wise this species is virtually identical to the common blacktip shark, from which it can be reliably distinguished only by its lower vertebra number and by genetic markers. Generally reaching 1.5–1.8 m (4.9–5.9 ft) in length, it is a fairly stout-bodied, bronze-colored shark with a long snout and black-tipped fins.

<i>Negaprion</i> Genus of sharks

Negaprion is a genus of requiem sharks in the family Carcharhinidae. It contains the two extant species of lemon sharks: the lemon shark of the Americas, and the sicklefin lemon shark of the Indo-Pacific. Both species are large, slow-moving, bulky sharks inhabiting shallow coastal waters, and can be identified by their short, blunt snouts, two dorsal fins of nearly equal size, and uniform yellowish brown or gray coloration.

<span class="mw-page-title-main">Tawny nurse shark</span> Species of shark

The tawny nurse shark is a species of carpet shark in the family Ginglymostomatidae, and the only extant member of the genus Nebrius.

<span class="mw-page-title-main">Australian weasel shark</span> Species of shark

The Australian weasel shark is an uncommon species of ground shark in the family Hemigaleidae. It inhabits shallow waters off northern Australia to a depth of 170 m (560 ft); smaller sharks frequent sand and seagrass habitat and shift to coral reefs as they grow older. A slim, drab species reaching a length of 1.1 m (3.6 ft), it has sickle-shaped fins with dark tips on the second dorsal fin and caudal fin upper lobe. Its upper teeth are broad with strong serrations only on the trailing edge. The lateral line along each side is prominent and exhibits a downward curve below the second dorsal fin.

<span class="mw-page-title-main">Sicklefin weasel shark</span> Species of shark

The sicklefin weasel shark is an uncommon species of ground shark in the family Hemigaleidae. It is native to southern India, southern China, and parts of Southeast Asia, living in shallow waters down to a depth of 170 m (560 ft). This lightly built shark is characterized by its very short mouth, broad upper teeth with serrations only on the trailing edge, and strongly sickle-shaped fins with obvious white tips on the two dorsal fins. It is light grey or bronze in colour, often with small white blotches on its sides; it reaches a maximum known length of 1.1 m (3.6 ft).

<span class="mw-page-title-main">Arabian carpetshark</span> Species of shark

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<i>Carcharias</i> Genus of sharks

Carcharias is a genus of mackerel sharks belonging to the family Odontaspididae. Once bearing many prehistoric species, all have gone extinct with the exception of the critically endangered sand tiger shark.

<span class="mw-page-title-main">Pink whipray</span> Species of stingray in the family Dasyatidae

The pink whipray is a species of stingray in the family Dasyatidae, with a wide but ill-defined distribution in the tropical Indo-Pacific from southern Africa to Polynesia. It is a bottom dweller that generally inhabits shallow water under 70 m (230 ft) deep, in sandy areas associated with coral reefs. Individuals exhibit a high degree of fidelity to particular locations. The pink whipray has a diamond-shaped pectoral fin disc wider than long, with a broad-angled snout and a very long, whip-like tail without fin folds. It has only a few small thorns on its back and is uniform brownish to grayish pink in color, becoming much darker past the tail sting. This large ray can reach 1.8 m (5.9 ft) across and over 5 m (16 ft) long.

<span class="mw-page-title-main">Lemon-striped pygmy hogfish</span> Species of fish

The lemon-striped pygmy hogfish is a species of ray-finned fish from the family Labridae, the wrasses. This species is found on reefs in the Coral Sea off the coast of Queensland and in French Polynesia.

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