Sicklefin lemon shark
Encyclopedia
The sicklefin lemon shark or sharptooth lemon shark (Negaprion acutidens) is a species
of requiem shark
, 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 fin
s 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 (12.5 ft) long. It generally inhabits water less than 92 m (301.8 ft) deep in a variety of habitat
s, from mangrove
estuaries
to coral reef
s.
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 10–11 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 International Union for Conservation of Nature (IUCN) has assessed this species as Vulnerable
; 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
.
, 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 (26.8 in) long individual caught in the Red Sea
off Jeddah
, Saudi Arabia
. 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.
Based on microsatellite DNA
evidence, the sicklefin lemon shark is thought to have diverged
from its sister species N. brevirostris 10–14 million years ago, when the closure of the Tethys Sea separated lemon sharks in the Indian Ocean
from those in the Atlantic. The ancestral lemon shark species may have been N. eurybathrodon
, whose fossil
ized teeth occur in both the United States
and Pakistan
. 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
).
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
. 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 (466 mi) apart, suggest that there is little intermingling between regional subpopulations.
An inhabitant of coastal continental and insular shelves
, the sicklefin lemon shark occurs from the intertidal zone
to a depth of 92 m (301.8 ft). This species favors still, murky waters and is most common in bay
s, estuaries
, and lagoon
s, and over sandy flats and outer reef
s. 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 mangrove
s, in water so shallow that their dorsal fins are exposed. 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
.
The sicklefin lemon shark has a robust, stocky body and a short, broad head. The snout is rounded or almost wedge-shaped, with small nostril
s bearing triangular flaps of skin in front. The eyes are small, and there are no spiracle
s. Short furrows are present at the corners of the mouth. There are 13–16 (usually 14) tooth rows 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. The teeth of sharks over 1.4 m (4.6 ft) long are finely serrated.
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. There is no ridge 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. The large dermal denticles are overlapping and bear 3–5 horizontal ridges each. The coloration is a plain yellowish brown or gray above and lighter below, with more yellow on the fins. This species attains a maximum known length of 3.8 m (12.5 ft), though it typically does not exceed 3.1 m (10.2 ft).
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. This shark seldom undertakes long-distance movements. A study at Aldabra Atoll in the Seychelles found that, of the tagged sharks that were later recaptured, over 90% were still within 2 km (1.2 mi) of their initial tagging location. 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.
Over 90% of the sicklefin lemon shark's diet consists of bottom and shore-dwelling teleosts, including herring
, mullet
s, mackerel
, silversides, needlefish
, smelt-whitings
, porgies
, sea catfish
, triggerfish
, parrotfish
, and porcupinefish
. Occasionally they may also take cephalopod
s and crustacean
s, and older individuals have been known to consume stingray
s and guitarfish
. This species may be preyed upon by larger sharks. Known parasites include the tapeworms Paraorygmatobothrium arnoldi, Pseudogrillotia spratti, Phoreiobothrium perilocrocodilus, and Platybothrium jondoeorum. Sicklefin lemon sharks have been documented resting on the bottom and eliciting cleanings by bluestreak cleaner wrasse
s (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.
As with other members of its family, the sicklefin lemon shark is viviparous, meaning the developing embryo
s are sustained by a placenta
l connection formed from their depleted yolk sac
s. Females give birth to 1–13 (usually 6–12) pups every other year in shallow nursery areas, following a gestation period
of 10–11 months. Unlike in the American lemon shark, there is scant evidence that this species is philopatric (returning to the site of their birth to reproduce). Parturition occurs in October or November at Madagascar and Aldabra, and in January at French Polynesia; ovulation
and mating
for non-pregnant 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 (17.7–31.5 in). 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).
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. At Moorea, sicklefin lemon sharks are the main attraction of daily shark-feeding ecotourism
dives. This shark adapts well to captivity and is displayed in public aquarium
s.
The International Union for Conservation of Nature (IUCN) has assessed the sicklefin lemon shark globally as Vulnerable
; it is harvested using anchored and floating gillnet
s, beach nets, and longlines. The meat is sold fresh or dried and salted for human consumption, the fins used for shark fin soup
, and the liver oil
processed for vitamin
s. 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 made extinct in parts of India
and Thailand
, and has not been reported from Indonesia
n 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
.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of requiem shark
Requiem shark
Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...
, family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Carcharhinidae, widely distributed in the tropical waters of the Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
. It is closely related to the better-known lemon shark
Lemon shark
The lemon shark, Negaprion brevirostris, is a shark in the family Carcharhinidae, that can grow to 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...
(N. brevirostris) of the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
; the two species are almost identical in appearance, both being stout-bodied sharks with broad heads, two dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s of nearly equal size, and a plain yellow-tinged coloration. As its common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
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 (12.5 ft) long. It generally inhabits water less than 92 m (301.8 ft) deep in a variety of habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s, from 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...
estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
to coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s.
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
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
of 10–11 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 International Union for Conservation of Nature (IUCN) has assessed this species as Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...
; its low reproductive productivity and rate of movement limits the capacity of depleted stocks to recover. Off India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
and Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
, this species has been severely depleted or extirpated by unregulated exploitation for its meat, fins, and liver oil
Shark liver oil
Shark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health...
.
Taxonomy and phylogeny
The sicklefin lemon shark was first described as Carcharias acutidens by German naturalist Eduard RüppellEduard Rüppell
Wilhelm Peter Eduard Simon Rüppell was a German naturalist and explorer. Rüppell is occasionally transliterated to "Rueppell" for the English alphabet....
, in the 1837 Fische des Rothen Meeres (Fishes of the Red Sea). In 1940, Australian ichthyologist Gilbert Percy Whitley
Gilbert Percy Whitley
Gilbert Percy Whitley was a British-born Australian ichthyologist and malacologist who was Curator of Fishes at the Australian Museum in Sydney for about 40 years. He was born at Swaythling, Southampton, England, and was educated at King Edward VI School, Southampton and Osborne House...
moved this species to his newly formed genus Negaprion. The type specimen, designated in 1960, is a 68 cm (26.8 in) long individual caught in the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
off Jeddah
Jeddah
Jeddah, Jiddah, Jidda, or Jedda is a city located on the coast of the Red Sea and is the major urban center of western Saudi Arabia. It is the largest city in Makkah Province, the largest sea port on the Red Sea, and the second largest city in Saudi Arabia after the capital city, Riyadh. The...
, Saudi Arabia
Saudi Arabia
The Kingdom of Saudi Arabia , commonly known in British English as Saudi Arabia and in Arabic as as-Sa‘ūdiyyah , is the largest state in Western Asia by land area, constituting the bulk of the Arabian Peninsula, and the second-largest in the Arab World...
. The specific epithet acutidens is derived from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
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.
Based on microsatellite DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
evidence, the sicklefin lemon shark is thought to have diverged
Genetic divergence
Genetic divergence is the process in which two or more populations of an ancestral species accumulate independent genetic changes through time, often after the populations have become reproductively isolated for some period of time...
from its sister species N. brevirostris 10–14 million years ago, when the closure of the Tethys Sea separated lemon sharks in the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
from those in the Atlantic. The ancestral lemon shark species may have been N. eurybathrodon
Negaprion
Negaprion is a genus of requiem sharks, family Carcharhinidae, containing the two extant species of lemon sharks: the lemon shark of the Americas, and the sicklefin lemon shark of the Indo-Pacific...
, whose fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
ized teeth occur in both the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
. Morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
and molecular phylogenetic analyses suggest that Negaprion is grouped with the whitetip reef shark
Whitetip reef shark
The whitetip reef shark is a species of requiem shark, family Carcharhinidae, and the only member of its genus. A small shark usually not exceeding 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...
(Triaenodon) and the sliteye shark
Sliteye shark
The sliteye shark the only member of the genus Loxodon, is a shark of the family Carcharhinidae, found in the tropical waters of the Indo-West Pacific oceans between latitudes 34° N and 30° S, from depths of 7 to 100 m. Its length is up to about 95 cm....
(Loxodon) in occupying an intermediate position on the carcharhinid evolutionary tree, between the most basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
genera (Galeocerdo, Rhizoprionodon
Rhizoprionodon
Rhizoprionodon is a genus of requiem sharks, family Carcharhinidae, commonly known as sharpnose sharks because of their long, pointed snouts.-Species:* Rhizoprionodon acutus...
, and Scoliodon) and the most derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
(Carcharhinus
Carcharhinus
Carcharhinus is the type genus of the requiem shark family, Carcharhinidae.- Species :* Carcharhinus acarenatus * Carcharhinus acronotus...
and Sphyrna
Sphyrna
Sphyrna is a genus of hammerhead sharks in the family Sphyrnidae. It currently consists of the following species:*Sphyrna corona S. Springer, 1940 *Sphyrna couardi Cadenat, 1951...
).
Distribution and habitat
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
to the Red Sea (including Mauritius
Mauritius
Mauritius , officially the Republic of Mauritius is an island nation off the southeast coast of the African continent in the southwest Indian Ocean, about east of Madagascar...
, the Seychelles
Seychelles
Seychelles , officially the Republic of Seychelles , is an island country spanning an archipelago of 115 islands in the Indian Ocean, some east of mainland Africa, northeast of the island of Madagascar....
, and Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
), continuing eastward along the coast of the Indian subcontinent
Indian subcontinent
The Indian subcontinent, also Indian Subcontinent, Indo-Pak Subcontinent or South Asian Subcontinent is a region of the Asian continent on the Indian tectonic plate from the Hindu Kush or Hindu Koh, Himalayas and including the Kuen Lun and Karakoram ranges, forming a land mass which extends...
to Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
, extending as far north as Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
and the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, and as far south as New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
and northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. This species is also found around numerous Pacific islands, including New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...
, Palau
Palau
Palau , officially the Republic of Palau , is an island nation in the Pacific Ocean, east of the Philippines and south of Tokyo. In 1978, after three decades as being part of the United Nations trusteeship, Palau chose independence instead of becoming part of the Federated States of Micronesia, a...
, the Marshall Islands
Marshall Islands
The Republic of the Marshall Islands , , is a Micronesian nation of atolls and islands in the middle of the Pacific Ocean, just west of the International Date Line and just north of the Equator. As of July 2011 the population was 67,182...
, the Solomon Islands
Solomon Islands
Solomon Islands is a sovereign state in Oceania, east of Papua New Guinea, consisting of nearly one thousand islands. It covers a land mass of . The capital, Honiara, is located on the island of Guadalcanal...
, Fiji
Fiji
Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...
, Vanuatu
Vanuatu
Vanuatu , officially the Republic of Vanuatu , is an island nation located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is some east of northern Australia, northeast of New Caledonia, west of Fiji, and southeast of the Solomon Islands, near New Guinea.Vanuatu was...
, and French Polynesia
French Polynesia
French Polynesia is an overseas country of the French Republic . It is made up of several groups of Polynesian islands, the most famous island being Tahiti in the Society Islands group, which is also the most populous island and the seat of the capital of the territory...
. 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 (466 mi) apart, suggest that there is little intermingling between regional subpopulations.
An inhabitant of coastal continental and insular shelves
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
, the sicklefin lemon shark occurs from the intertidal zone
Intertidal zone
The intertidal zone is the area that is above water at low tide and under water at high tide . This area can include many different types of habitats, with many types of animals like starfish, sea urchins, and some species of coral...
to a depth of 92 m (301.8 ft). This species favors still, murky waters and is most common in bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s, estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
, and lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s, and over sandy flats and outer reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s. Sometimes an individual may venture into open water
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
; one was filmed in the 1971 documentary
Documentary
A documentary is a creative work of non-fiction, including:* Documentary film, including television* Radio documentary* Documentary photographyRelated terms include:...
Blue Water, White Death, in the vicinity of a sperm whale
Sperm Whale
The sperm whale, Physeter macrocephalus, is a marine mammal species, order Cetacea, a toothed whale having the largest brain of any animal. The name comes from the milky-white waxy substance, spermaceti, found in the animal's head. The sperm whale is the only living member of genus Physeter...
(Physeter macrocephalus) carcass. Juvenile sicklefin lemon sharks are often found on reef flats or around 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, in water so shallow that their dorsal fins are exposed. In Herald Bight off Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
, 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
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
Posidonia australis
Posidonia australis
Posidonia australis is a species of seagrass that occurs in the southern waters of Australia. It is sometimes referred to as Fibreball Weed. The marine plant forms large meadows that are considered to be of high importance to the environmental conservation of the region...
.
Description
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s bearing triangular flaps of skin in front. The eyes are small, and there are no spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s. Short furrows are present at the corners of the mouth. There are 13–16 (usually 14) tooth rows 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. The teeth of sharks over 1.4 m (4.6 ft) long are finely serrated.
The fins (especially the dorsal
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
, 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. There is no ridge 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. The large dermal denticles are overlapping and bear 3–5 horizontal ridges each. The coloration is a plain yellowish brown or gray above and lighter below, with more yellow on the fins. This species attains a maximum known length of 3.8 m (12.5 ft), though it typically does not exceed 3.1 m (10.2 ft).
Biology and ecology
Moorea
Moʻorea is a high island in French Polynesia, part of the Society Islands, 17 km northwest of Tahiti. Its position is . Moʻorea means "yellow lizard" in Tahitian...
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.
Over 90% of the sicklefin lemon shark's diet consists of bottom and shore-dwelling teleosts, including herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
, mullet
Mullet (fish)
The mullets or grey mullets are a family and order of ray-finned fish found worldwide in coastal temperate and tropical waters, and in some species in fresh water. Mullets have served as an important source of food in Mediterranean Europe since Roman times...
s, mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
, silversides, needlefish
Needlefish
Needlefish are piscivorous fishes primarily associated with very shallow marine habitats or the surface of the open sea. Some genera include species found in marine, brackish, and freshwater environments while a few genera are confined to freshwater rivers and streams, including Belonion,...
, smelt-whitings
Sillaginidae
The Sillaginidae, commonly known as the smelt-whitings, whitings, sillaginids, sand borers and sand-smelts, are a family of benthic coastal marine fishes in the order Perciformes. The smelt-whitings inhabit a wide region covering much of the Indo-Pacific, from the west coast of Africa east to Japan...
, porgies
Sparidae
The Sparidae is a family of fish, included in the order Perciformes. The fish of the family are commonly called sea breams and porgies . The sheepshead, scup, and red sea bream are species in this family. They are found in shallow temperate and tropical waters and are bottom-dwelling carnivores....
, sea catfish
Ariidae
The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones.-Taxonomy:...
, triggerfish
Triggerfish
Triggerfishes are about 40 species of often brightly colored fishes of the family Balistidae. Often marked by lines and spots, they inhabit tropical and subtropical oceans throughout the world, with the greatest species richness in the Indo-Pacific...
, parrotfish
Parrotfish
Parrotfishes are a group of fishes that traditionally had been considered a family , but now often are considered a subfamily of the wrasses. They are found in relatively shallow tropical and subtropical oceans throughout the world, but with the largest species richness in the Indo-Pacific...
, and porcupinefish
Porcupinefish
Porcupinefish are fish of the family Diodontidae, , also commonly called blowfish ....
. Occasionally they may also take cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s and crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, and older individuals have been known to consume stingray
Stingray
The stingrays are a group of rays, which are cartilaginous fishes related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes, and consist of eight families: Hexatrygonidae , Plesiobatidae , Urolophidae , Urotrygonidae , Dasyatidae , Potamotrygonidae The...
s and guitarfish
Guitarfish
The guitarfish are a family, Rhinobatidae, of rays. The guitarfish are known for an elongated body with a flattened head and trunk and small ray like wings. The combined range of the various species is tropical, subtropical and temperate waters worldwide. They often travel in large...
. This species may be preyed upon by larger sharks. Known parasites include the tapeworms Paraorygmatobothrium arnoldi, Pseudogrillotia spratti, Phoreiobothrium perilocrocodilus, and Platybothrium jondoeorum. Sicklefin lemon sharks have been documented resting on the bottom and eliciting cleanings by bluestreak cleaner wrasse
Bluestreak cleaner wrasse
The bluestreak cleaner wrasse is one of several species of cleaner wrasse found on coral reefs in the Indian Ocean and much of the Pacific Ocean, as well as many seas, including the Red Sea and those around Southeast Asia...
s (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.
As with other members of its family, the sicklefin lemon shark is viviparous, meaning the developing embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s are sustained by a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection formed from their depleted yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
s. Females give birth to 1–13 (usually 6–12) pups every other year in shallow nursery areas, following a gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
of 10–11 months. Unlike in the American lemon shark, there is scant evidence that this species is philopatric (returning to the site of their birth to reproduce). Parturition occurs in October or November at Madagascar and Aldabra, and in January at French Polynesia; ovulation
Ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...
and mating
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
for non-pregnant 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 (17.7–31.5 in). 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
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at a length of 2.2–2.4 m (7.2–7.9 ft).
Human interactions
Shark attack
A shark attack is an attack on a human by a shark. Every year around 60 shark attacks are reported worldwide, although death is quite unusual. Despite the relative rarity of shark attacks, the fear of sharks is a common phenomenon, having been fueled by the occasional instances of serial attacks,...
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. At Moorea, sicklefin lemon sharks are the main attraction of daily shark-feeding ecotourism
Ecotourism
Ecotourism is a form of tourism visiting fragile, pristine, and usually protected areas, intended as a low impact and often small scale alternative to standard commercial tourism...
dives. This shark adapts well to captivity and is displayed in public aquarium
Public aquarium
A public aquarium is the aquatic counterpart of a zoo, housing living aquatic species for viewing. Most public aquariums feature tanks larger than those kept by home aquarists, as well as smaller tanks. Since the first public aquariums were built in the mid-19th century, they have become popular...
s.
The International Union for Conservation of Nature (IUCN) has assessed the sicklefin lemon shark globally as Vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...
; it is harvested using anchored and floating gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
s, beach nets, and longlines. The meat is sold fresh or dried and salted for human consumption, the fins used for shark fin soup
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
, and the liver oil
Shark liver oil
Shark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health...
processed for vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
s. The sicklefin lemon shark is highly susceptible to local overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
, 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
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
, and has been assessed there as Endangered by the IUCN. Widespread habitat degradation, including pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
and blast fishing
Blast fishing
Blast fishing or dynamite fishing is the practice of using explosives to stun or kill schools of fish for easy collection. This often illegal practice can be extremely destructive to the surrounding ecosystem, as the explosion often destroys the underlying habitat that supports the fish...
on coral reefs and deforestation
Deforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....
in mangroves, poses an additional threat to the survival of this species in the region. Already, the sicklefin lemon shark has been made extinct in parts of India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
and Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, and has not been reported from Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
n 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
Bycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
, and has been listed under Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
.