Tawny nurse shark
Encyclopedia
The tawny nurse shark is a species
of carpet shark
in the family
Ginglymostomatidae, and the only extant member of the genus
Nebrius
. It is found widely along coastlines in the Indian
and Pacific Ocean
s, preferring reef
s, sandy flats, and seagrass
beds from very shallow water to a depth of 70 m (230 ft). With a cylindrical body and a broad, flattened head, the tawny nurse shark is quite similar in appearance to the nurse shark
(Ginglymostoma cirratum) of the Americas
, from which it can be distinguished by its pointed-tipped dorsal fins and narrow, sickle-shaped pectoral fins. The maximum recorded length is 3.2 m (10.5 ft).
Nocturnal in habits, the tawny nurse shark tends to spend the day resting in piles of two dozen or more individuals inside caves or under ledges. At night, it is an active-swimming predator that uses a powerful suction
force to extract prey from inside holes and crevices. The diet of this species consists mainly of octopus
, though they also take other invertebrate
s, small bony fishes, and rarely sea snakes. It is aplacental viviparous, meaning the embryo
s hatch from egg capsules
inside the mother. It is the only carpet shark in which the embryos are oophagous
, feeding on eggs
produced by the mother while inside the uterus
. The litter size may be as small as one or two, based on the large size of near-term embryos.
Compared to the nurse shark, the tawny nurse shark has a more placid disposition and will often allow divers to touch and play with it. However, it should be accorded respect due to its powerful jaws and sharp teeth. This species is caught by commercial fisheries
across most of its range for meat, fins, liver oil
, leather
, and fishmeal. It is also esteemed as a game fish
off Queensland
, Australia
, and is known for its habit of spitting water in the faces of its captors. The International Union for Conservation of Nature (IUCN) has assessed the tawny nurse shark as Vulnerable
, with subpopulations in several areas already diminished or extirpated.
as Scyllium ferrugineum, based on a 1.4 m (4.6 ft) long specimen from New Guinea
. His short account was published in 1831 in Voyage au tour du monde, sur la corvette La Coquille. A more detailed description, along with an illustration, was published by German naturalist Eduard Rüppell
in 1837 as Nebrius concolor, based on a specimen from the Red Sea
. Both names were retained, often in separate genera (Ginglymostoma and Nebrius respectively), until they were synonymized
by Leonard Compagno
in 1984. Compagno recognized that the tooth shape differences used to separate these species were the result of differences in age, with N. concolor representing younger individuals.
The genus name Nebrius is derived from the Greek word nebris or nebridos, meaning the skin of a fawn. The specific epithet ferrugineus is Latin
for "rust-colored". Other common names for this species include giant sleepy shark, Madame X (a name coined by the shark fisherman Norman Caldwell in the 1930s for the then-unidentified Australian specimens), nurse shark, rusty catshark, rusty shark, sleepy shark, spitting shark, and tawny shark. Based on morphological
similarities, Nebrius is believed to be the sister genus of Ginglymostoma, with both being placed in a clade
that also contains the short-tail nurse shark (Pseudoginglymostoma brevicaudatum), the whale shark
(Rhincodon typus), and the zebra shark
(Stegostoma fasciatum).
, South Africa
northward to the Red Sea
, Persian Gulf
and India
, including Madagascar
, Mauritius
, the Chagos Archipelago
, the Seychelles
, and the Maldives
. In the western Pacific, it occurs from southern Japan
and the coast of China
to the Philippines
, Southeast Asia
, and Indonesia
, to as far south as the northern coast of Australia. In the central Pacific, it has been reported from off New Caledonia
, Samoa
, Palau
, the Marshall Islands
, and Tahiti
. Fossil teeth belonging to this species have been found in the Pirabas Formation of northern Brazil
, dating back to the Lower Miocene (23–16 Ma). The presence of these fossils indicates that the range of the tawny nurse shark once extended to the tropical Atlantic Ocean
, prior to the formation of the Isthmus of Panama
.
An inshore species, the tawny nurse shark inhabits continental
and insular shelves over sandy flats or beds of seagrass
, as well as along the outer edges of coral
or rocky reef
s. This shark may be found from the surf zone
, often in water barely deep enough to cover its body, to a maximum depth of 70 m (320 ft) on coral reefs; it is most common at a depth of 5–30 m (16–100 ft). Young sharks are generally found in the shallow areas of lagoon
s, while adults may be encountered across a variety of habitats.
s behind. There are a pair of long, slender barbels
in front of the nostrils. The mouth is small, with the lower lip divided into three lobes. There are 29–33 tooth rows in the upper jaw and 26–28 tooth rows in the lower jaw, arranged in an imbricate (overlapping) pattern with the outermost 2–4 functional rows separated from the rest by a narrow space. Each tooth resembles a fan
, with a broad base rising to a small, sharp central point flanked by 3 or more smaller cusps on both sides. As the shark ages, the teeth become relatively taller and thicker. The fourth and fifth pairs of gill slit
s are placed much closer together than the others.
The dorsal and pelvic fins are angular, with the first dorsal fin larger than the second. The pectoral fins are narrow, pointed, and falcate (sickle-shaped); their shape separates this species from the similar-looking nurse shark. The origin of the first dorsal fin is about even with the origin of the pelvic fins, while the origin of the anal fin is even with or somewhat behind the origin of the second dorsal fin. The caudal fin has a shallow upper lobe and barely present lower lobe, comprising about a quarter of the total length in adults. The dermal denticles are diamond-shaped, bearing 4–5 faint ridges radiating from a blunt point. Tawny nurse sharks are yellowish, reddish, or grayish brown above and off-white below, and are capable of slowly changing their color to better blend with the environment. Young sharks have starkly white lower eyelids.
Many tawny nurse sharks found off the coasts of Japan, Taiwan, and the Ryukyu Islands lack a second dorsal fin. This physical abnormality has been speculated to result from pregnant females being exposed to water of unusually high salinity
and/or temperature
, possibly from human activity. In 1986, a 2.9 m (9.5 ft) long adult male with both a missing dorsal fin and partial albinism
(in the form of white body color with gray-brown eyes) was captured off Wakayama Prefecture
, Japan. This anomalous individual is the largest albino shark known to date, having survived for a long time in the wild despite its lack of camouflage
.
(Negaprion acutidens). Tawny nurse sharks are primarily nocturnal, though they are said to be active at all hours off Madagascar, and in captivity they will become diurnally active if presented with food. During the day, groups of two dozen or more sharks can be found resting inside caves and under ledges, often stacked atop one another. Individual sharks have small home ranges that they consistently return to each day.
The tawny nurse shark has few natural predators; attacks on this species have been reported from bull shark
s (Carcharhinus leucas) and great hammerhead
s (Sphyrna mokarran), while the related nurse shark has been known to fall prey to tiger shark
s (Galeocerdo cuvier) and lemon shark
s (Negaprion brevirostris). Known parasites
of this species include five species of tapeworms in the genus Pedibothrium, which infest the shark's spiral intestine
.
s, sea urchin
s, crustacean
s (e.g. crab
s and lobster
s), squid
, small fishes (e.g. surgeonfish, queenfish
, and rabbitfish), and the occasional sea snake. Hunting tawny nurse sharks swim slowly just above the sea floor, poking their heads into depressions and holes. When a prey item is found, the shark forcefully expands its large, muscular pharynx
, creating a powerful negative pressure that sucks the prey into its mouth.
and two functional uteruses. The mode of reproduction is aplacental viviparity, meaning that the embryo
s hatch inside the uterus; females in captivity have been documented depositing up to 52 non-viable egg capsules, which has led to erroneous reports of this shark being oviparous. The egg capsules of this species are onion-shaped, with thin, brown, translucent shells. The tawny nurse shark is the only carpet shark in which there is oophagy
: once the developing embryos exhaust their supply of yolk, they gorge on eggs produced by the mother and acquire the distended abdomen characteristic of such oophagous embryos. Unlike in mackerel shark
s, the eggs consumed by the embryos are large and shelled rather than small and undeveloped. There is no evidence of sibling cannibalism as in the sand tiger shark (Carcharias taurus).
Various authors have reported the length at birth anywhere from 40 cm (16 in) to 80 cm (31 in), with the discrepancy possibly reflecting geographic variation. Although females release up to four fertilized eggs into each uterus, the very large size of the newborns suggest that the litter size may be as few as one or two. In one examined female that had two embryos sharing a single uterus, one embryo was much smaller and thinner than the other, implying that competition may eliminate the additional siblings. Males attain sexual maturity
at a length of 2.5 m (8.2 ft), and females at a length of 2.3–2.9 m (7.5–9.5 ft).
Encounters with tawny nurse sharks underwater indicate a more docile demeanor than the similar nurse shark; usually divers are able to approach the sharks closely and even touch and play with them without incident. However, this species has been infrequently provoked into biting, and merits respect due to its strength, small but sharp teeth, and extremely powerful jaws. Tawny nurse sharks are favored attractions for ecotourist divers
off Thailand
, the Solomon Islands
, and elsewhere. This species also adapts well to captivity and is displayed in public aquaria in Europe
, the United States
, Okinawa, and Singapore
, where they may become tame enough to be hand-fed.
The tawny nurse shark is taken by commercial fisheries operating throughout its range, including off Pakistan, India, Thailand, and the Philippines; an exception is in Australian waters, where it is only taken in small numbers as bycatch
. This shark is caught using demersal trawls, floating and fixed bottom gill nets, and on hook-and-line. The meat is sold fresh or dried and salted, the fins are used for shark fin soup
, and the offal
processed into fishmeal. In addition, the liver is a source of oil and vitamins, and the thick, tough skin is made into leather products. Off Queensland, Australia, the tawny nurse shark is valued by big-game anglers. When hooked, large individuals are tenacious opponents and are difficult to subdue due to their habit of spinning. They are also capable of spitting a powerful jet of water into the faces of their captors, making grunting noises in between jets; whether this is a deliberate defensive behavior is uncertain.
The International Union for Conservation of Nature (IUCN) has assessed the tawny nurse shark as Vulnerable worldwide, as it faces heavy fishing pressure and its low reproductive and dispersal rates limit the ability of over-exploited populations to recover. Furthermore, this shark's inshore habitat renders it susceptible to habitat degradation, destructive fishing practices (e.g. poisons and explosives, especially prevalent off Indonesia and the Philippines), and human harassment. Localized declines or extirpations of the tawny nurse shark have been documented off India and Thailand. Off Australia, this species has been assessed as of Least Concern
, as there it is not targeted by fisheries.
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 carpet shark
Carpet shark
The carpet sharks are an order, Orectolobiformes, of sharks, so called because many members have ornate patterns reminiscent of carpets....
in the 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...
Ginglymostomatidae, and the only extant member of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Nebrius
Nebrius
Nebrius is a genus of carpet sharks in the family Ginglymostomatidae. It contains a single extant species, the tawny nurse shark , as well as a number of extinct species dating back to the Early Paleocene....
. It is found widely along coastlines in the Indian
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...
and Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
s, preferring reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s, sandy flats, and 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:...
beds from very shallow water to a depth of 70 m (230 ft). With a cylindrical body and a broad, flattened head, the tawny nurse shark is quite similar in appearance to the nurse shark
Nurse shark
The nurse shark, Ginglymostoma cirratum, sometimes referred to as the Nur Shark is a shark in the nurse sharks family, the only member of its genus Ginglymostoma...
(Ginglymostoma cirratum) 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...
, from which it can be distinguished by its pointed-tipped dorsal fins and narrow, sickle-shaped pectoral fins. The maximum recorded length is 3.2 m (10.5 ft).
Nocturnal in habits, the tawny nurse shark tends to spend the day resting in piles of two dozen or more individuals inside caves or under ledges. At night, it is an active-swimming predator that uses a powerful suction
Suction
Suction is the flow of a fluid into a partial vacuum, or region of low pressure. The pressure gradient between this region and the ambient pressure will propel matter toward the low pressure area. Suction is popularly thought of as an attractive effect, which is incorrect since vacuums do not...
force to extract prey from inside holes and crevices. The diet of this species consists mainly of octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
, though they also take other invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, small bony fishes, and rarely sea snakes. It is aplacental viviparous, meaning the 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 hatch from egg capsules
Mermaid's purse
An egg case or egg capsule, colloquially known as a mermaid's purse or devil's purse, is a casing that surrounds the fertilized eggs of some sharks, skates, and chimaeras. They are among the common objects which are washed up by the sea. They are made of collagen protein strands...
inside the mother. It is the only carpet shark in which the embryos are oophagous
Oophagy
Oophagy , literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek ᾠόν and classical Greek φᾱγεῖν ....
, feeding on eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
produced by the mother while inside the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
. The litter size may be as small as one or two, based on the large size of near-term embryos.
Compared to the nurse shark, the tawny nurse shark has a more placid disposition and will often allow divers to touch and play with it. However, it should be accorded respect due to its powerful jaws and sharp teeth. This species is caught by commercial fisheries
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
across most of its range for meat, fins, 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...
, leather
Leather
Leather is a durable and flexible material created via the tanning of putrescible animal rawhide and skin, primarily cattlehide. It can be produced through different manufacturing processes, ranging from cottage industry to heavy industry.-Forms:...
, and fishmeal. It is also esteemed as a game fish
Game fish
Game fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...
off Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
, 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...
, and is known for its habit of spitting water in the faces of its captors. The International Union for Conservation of Nature (IUCN) has assessed the tawny nurse shark 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:...
, with subpopulations in several areas already diminished or extirpated.
Taxonomy and phylogeny
The tawny nurse shark was first described by French naturalist René-Primevère LessonRené-Primevère Lesson
René Primevère Lesson was a French surgeon, naturalist, ornithologist, and herpetologist.Lesson was born at Rochefort, and at the age of sixteen he entered the Naval Medical School there...
as Scyllium ferrugineum, based on a 1.4 m (4.6 ft) long specimen from 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...
. His short account was published in 1831 in Voyage au tour du monde, sur la corvette La Coquille. A more detailed description, along with an illustration, was published by German naturalist Eduard Rüppell
Eduard Rüppell
Wilhelm Peter Eduard Simon Rüppell was a German naturalist and explorer. Rüppell is occasionally transliterated to "Rueppell" for the English alphabet....
in 1837 as Nebrius concolor, based on a specimen from 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...
. Both names were retained, often in separate genera (Ginglymostoma and Nebrius respectively), until they were synonymized
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
by Leonard Compagno
Leonard Compagno
Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...
in 1984. Compagno recognized that the tooth shape differences used to separate these species were the result of differences in age, with N. concolor representing younger individuals.
The genus name Nebrius is derived from the Greek word nebris or nebridos, meaning the skin of a fawn. The specific epithet ferrugineus is 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...
for "rust-colored". Other common names for this species include giant sleepy shark, Madame X (a name coined by the shark fisherman Norman Caldwell in the 1930s for the then-unidentified Australian specimens), nurse shark, rusty catshark, rusty shark, sleepy shark, spitting shark, and tawny shark. Based on 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....
similarities, Nebrius is believed to be the sister genus of Ginglymostoma, with both being placed in a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
that also contains the short-tail nurse shark (Pseudoginglymostoma brevicaudatum), the whale shark
Whale shark
The whale shark, Rhincodon typus, is a slow-moving filter feeding shark, the largest extant fish species. The largest confirmed individual had a length of and a weight of more than , but unconfirmed claims report considerably larger whale sharks...
(Rhincodon typus), and the zebra shark
Zebra shark
The zebra shark is a species of carpet shark and the sole member of the family Stegostomatidae. It is found throughout the tropical Indo-Pacific, frequenting coral reefs and sandy flats to a depth of 62 m...
(Stegostoma fasciatum).
Distribution and habitat
The tawny nurse shark is widely distributed in the Indo-Pacific region. In the Indian Ocean, it is found from KwaZulu-NatalKwaZulu-Natal
KwaZulu-Natal is a province of South Africa. Prior to 1994, the territory now known as KwaZulu-Natal was made up of the province of Natal and the homeland of KwaZulu....
, South Africa
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...
northward to 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...
, Persian Gulf
Persian Gulf
The Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...
and 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...
, including Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
, 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 Chagos Archipelago
Chagos Archipelago
The Chagos Archipelago , is a group of seven atolls comprising more than 60 individual tropical islands in the Indian Ocean; situated some due south of the Maldives archipelago. This chain of islands are the southernmost archipelago of the Chagos-Laccadive Ridge a long submarine mountain range...
, 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 the Maldives
Maldives
The Maldives , , officially Republic of Maldives , also referred to as the Maldive Islands, is an island nation in the Indian Ocean formed by a double chain of twenty-six atolls oriented north-south off India's Lakshadweep islands, between Minicoy Island and...
. In the western Pacific, it occurs from southern Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and the coast of China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
to 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...
, 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...
, and 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...
, to as far south as the northern coast of Australia. In the central Pacific, it has been reported from off 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...
, Samoa
Samoa
Samoa , officially the Independent State of Samoa, formerly known as Western Samoa is a country encompassing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and one of the biggest islands in...
, 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...
, and Tahiti
Tahiti
Tahiti is the largest island in the Windward group of French Polynesia, located in the archipelago of the Society Islands in the southern Pacific Ocean. It is the economic, cultural and political centre of French Polynesia. The island was formed from volcanic activity and is high and mountainous...
. Fossil teeth belonging to this species have been found in the Pirabas Formation of northern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, dating back to the Lower Miocene (23–16 Ma). The presence of these fossils indicates that the range of the tawny nurse shark once extended to the tropical Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, prior to the formation of the Isthmus of Panama
Isthmus of Panama
The Isthmus of Panama, also historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country of Panama and the Panama Canal...
.
An inshore species, the tawny nurse shark inhabits continental
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,...
and insular shelves over sandy flats or beds of 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:...
, as well as along the outer edges of coral
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...
or rocky reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s. This shark may be found from the surf zone
Surf zone
As ocean surface waves come closer to shore they break, forming the foamy, bubbly surface we call surf. The region of breaking waves defines the surf zone. After breaking in the surf zone, the waves continue to move in, and they run up onto the sloping front of the beach, forming an uprush of...
, often in water barely deep enough to cover its body, to a maximum depth of 70 m (320 ft) on coral reefs; it is most common at a depth of 5–30 m (16–100 ft). Young sharks are generally found in the shallow areas of 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, while adults may be encountered across a variety of habitats.
Description
The tawny nurse shark grows to a maximum length of 3.2 m (10.5 ft). It has a robust, cylindrical body with a broadly rounded and flattened head. The eyes are small and face laterally, with prominent ridges over them and smaller spiracleSpiracle
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 behind. There are a pair of long, slender barbels
Barbel (anatomy)
A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...
in front of the nostrils. The mouth is small, with the lower lip divided into three lobes. There are 29–33 tooth rows in the upper jaw and 26–28 tooth rows in the lower jaw, arranged in an imbricate (overlapping) pattern with the outermost 2–4 functional rows separated from the rest by a narrow space. Each tooth resembles a fan
Fan (implement)
A hand-held fan is an implement used to induce an airflow for the purpose of cooling or refreshing oneself. Any broad, flat surface waved back-and-forth will create a small airflow and therefore can be considered a rudimentary fan...
, with a broad base rising to a small, sharp central point flanked by 3 or more smaller cusps on both sides. As the shark ages, the teeth become relatively taller and thicker. The fourth and fifth pairs of gill slit
Gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s are placed much closer together than the others.
The dorsal and pelvic fins are angular, with the first dorsal fin larger than the second. The pectoral fins are narrow, pointed, and falcate (sickle-shaped); their shape separates this species from the similar-looking nurse shark. The origin of the first dorsal fin is about even with the origin of the pelvic fins, while the origin of the anal fin is even with or somewhat behind the origin of the second dorsal fin. The caudal fin has a shallow upper lobe and barely present lower lobe, comprising about a quarter of the total length in adults. The dermal denticles are diamond-shaped, bearing 4–5 faint ridges radiating from a blunt point. Tawny nurse sharks are yellowish, reddish, or grayish brown above and off-white below, and are capable of slowly changing their color to better blend with the environment. Young sharks have starkly white lower eyelids.
Many tawny nurse sharks found off the coasts of Japan, Taiwan, and the Ryukyu Islands lack a second dorsal fin. This physical abnormality has been speculated to result from pregnant females being exposed to water of unusually high salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
and/or temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, possibly from human activity. In 1986, a 2.9 m (9.5 ft) long adult male with both a missing dorsal fin and partial albinism
Albinism
Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin...
(in the form of white body color with gray-brown eyes) was captured off Wakayama Prefecture
Wakayama Prefecture
is a prefecture of Japan located on the Kii Peninsula in the Kansai region on Honshū island. The capital is the city of Wakayama.- History :Present-day Wakayama is mostly the western part of the province of Kii.- 1953 Wakayama Prefecture flood disaster :...
, Japan. This anomalous individual is the largest albino shark known to date, having survived for a long time in the wild despite its lack of camouflage
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...
.
Biology and ecology
With a more streamlined form than other nurse sharks, the tawny nurse shark is believed to be a less benthic, more active swimmer. The characteristics of its body, head, fins, and teeth are comparable to other active reef sharks sharing its range, such as the sicklefin lemon sharkSicklefin lemon shark
The sicklefin lemon shark or sharptooth lemon shark 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 The sicklefin lemon shark or sharptooth lemon shark (Negaprion acutidens)...
(Negaprion acutidens). Tawny nurse sharks are primarily nocturnal, though they are said to be active at all hours off Madagascar, and in captivity they will become diurnally active if presented with food. During the day, groups of two dozen or more sharks can be found resting inside caves and under ledges, often stacked atop one another. Individual sharks have small home ranges that they consistently return to each day.
The tawny nurse shark has few natural predators; attacks on this species have been reported from bull shark
Bull shark
The bull shark, Carcharhinus leucas, also known as Zambezi shark or unofficially known as Zambi in Africa and Nicaragua shark in Nicaragua, is a shark common worldwide in warm, shallow waters along coasts and in rivers...
s (Carcharhinus leucas) and great hammerhead
Great hammerhead
The great hammerhead is the largest species of hammerhead shark, family Sphyrnidae, attaining a maximum length of 6.1 m . It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the continental shelf...
s (Sphyrna mokarran), while the related nurse shark has been known to fall prey to tiger shark
Tiger shark
The tiger sharks, Galeocerdo cuvier, is a species of requiem shark and the only member of the genus Galeocerdo. Commonly known as sea tigers, tiger sharks are relatively large macropredators, capable of attaining a length of over . It is found in many tropical and temperate waters, and is...
s (Galeocerdo cuvier) and 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...
s (Negaprion brevirostris). Known parasites
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
of this species include five species of tapeworms in the genus Pedibothrium, which infest the shark's spiral intestine
Spiral valve
A spiral valve is the lower portion of the intestine of some sharks, rays, skates and bichirs. A modification of the ileum, the spiral valve is internally twisted or coiled to increase the surface area of the intestine, to increase nutrient absorption....
.
Feeding
The tawny nurse shark may be one of the few fishes specializing in preying on octopus. Other known food items include coralCoral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
s, sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
s, 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 (e.g. crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s and lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
s), squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
, small fishes (e.g. surgeonfish, queenfish
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
, and rabbitfish), and the occasional sea snake. Hunting tawny nurse sharks swim slowly just above the sea floor, poking their heads into depressions and holes. When a prey item is found, the shark forcefully expands its large, muscular pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
, creating a powerful negative pressure that sucks the prey into its mouth.
Life history
Mating in the tawny nurse shark is known to occur from July to August off Madagascar. Adult females have one functional ovaryOvary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
and two functional uteruses. The mode of reproduction is aplacental viviparity, meaning that the 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 hatch inside the uterus; females in captivity have been documented depositing up to 52 non-viable egg capsules, which has led to erroneous reports of this shark being oviparous. The egg capsules of this species are onion-shaped, with thin, brown, translucent shells. The tawny nurse shark is the only carpet shark in which there is oophagy
Oophagy
Oophagy , literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek ᾠόν and classical Greek φᾱγεῖν ....
: once the developing embryos exhaust their supply of yolk, they gorge on eggs produced by the mother and acquire the distended abdomen characteristic of such oophagous embryos. Unlike in mackerel shark
Lamniformes
Lamniformes is an order of sharks commonly known as mackerel sharks . It includes some of the most familiar species of sharks, such as the great white shark, as well as more unusual representatives, such as the goblin shark and the megamouth shark.Members of the order are distinguished by...
s, the eggs consumed by the embryos are large and shelled rather than small and undeveloped. There is no evidence of sibling cannibalism as in the sand tiger shark (Carcharias taurus).
Various authors have reported the length at birth anywhere from 40 cm (16 in) to 80 cm (31 in), with the discrepancy possibly reflecting geographic variation. Although females release up to four fertilized eggs into each uterus, the very large size of the newborns suggest that the litter size may be as few as one or two. In one examined female that had two embryos sharing a single uterus, one embryo was much smaller and thinner than the other, implying that competition may eliminate the additional siblings. Males 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 2.5 m (8.2 ft), and females at a length of 2.3–2.9 m (7.5–9.5 ft).
Human interactions
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...
off 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...
, 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...
, and elsewhere. This species also adapts well to captivity and is displayed in public aquaria in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, Okinawa, and Singapore
Singapore
Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
, where they may become tame enough to be hand-fed.
The tawny nurse shark is taken by commercial fisheries operating throughout its range, including off Pakistan, India, Thailand, and the Philippines; an exception is in Australian waters, where it is only taken in small numbers 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...
. This shark is caught using demersal trawls, floating and fixed bottom gill nets, and on hook-and-line. The meat is sold fresh or dried and salted, the fins are 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 offal
Offal
Offal , also called, especially in the United States, variety meats or organ meats, refers to the internal organs and entrails of a butchered animal. The word does not refer to a particular list of edible organs, which varies by culture and region, but includes most internal organs other than...
processed into fishmeal. In addition, the liver is a source of oil and vitamins, and the thick, tough skin is made into leather products. Off Queensland, Australia, the tawny nurse shark is valued by big-game anglers. When hooked, large individuals are tenacious opponents and are difficult to subdue due to their habit of spinning. They are also capable of spitting a powerful jet of water into the faces of their captors, making grunting noises in between jets; whether this is a deliberate defensive behavior is uncertain.
The International Union for Conservation of Nature (IUCN) has assessed the tawny nurse shark as Vulnerable worldwide, as it faces heavy fishing pressure and its low reproductive and dispersal rates limit the ability of over-exploited populations to recover. Furthermore, this shark's inshore habitat renders it susceptible to habitat degradation, destructive fishing practices (e.g. poisons and explosives, especially prevalent off Indonesia and the Philippines), and human harassment. Localized declines or extirpations of the tawny nurse shark have been documented off India and Thailand. Off Australia, this species has been assessed as of 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...
, as there it is not targeted by fisheries.