The tawny nurse shark (''Nebrius ferrugineus'') is a
species
In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
of
carpet shark in the
family Ginglymostomatidae, and the only extant member of the
genus ''
Nebrius''.
It is found widely along
coastline
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in ...
s in the
Indo-Pacific, preferring
reefs,
sandy flats, and
seagrass
Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families ( Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the ...
beds from very shallow water to a depth of . With a cylindrical body and a broad, flattened head, the tawny nurse shark is quite similar in appearance to the
nurse shark
The nurse shark (''Ginglymostoma cirratum'') is an elasmobranch fish in the family Ginglymostomatidae. The conservation status of the nurse shark is globally assessed as Vulnerable in the IUCN List of Threatened Species. They are considered t ...
(''Ginglymostoma cirratum'') of the Atlantic and East Pacific, from which it can be distinguished by its pointed-tipped
dorsal fins and narrow, sickle-shaped
pectoral fin
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...
s. The maximum recorded length of the tawny nurse shark is .
Nocturnal
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Nocturnal creatures generally have highly developed sens ...
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
An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlef ...
, though they also take other
invertebrates, small
bony fish
Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...
es, and rarely
sea snakes. It is
aplacental viviparous, meaning the
embryos hatch from
egg capsules inside the mother. It is the only carpet shark in which the embryos are
oophagous
Oophagy ( ) sometimes ovophagy, 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 (, "egg") and classical Greek (, ...
, feeding on
eggs
Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
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
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 ...
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
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of nat ...
(IUCN) has assessed the tawny nurse shark as
Vulnerable, with subpopulations in several areas already diminished or
extirpated.
Taxonomy and phylogeny
The tawny nurse shark was first described by French naturalist
René-Primevère Lesson as ''Scyllium ferrugineum'', based on a 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 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 Organi ...
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".
[Bester, C]
Biological Profiles: Tawny Nurse Shark
. Florida Museum of Natural History Ichthyology Department. Retrieved on June 7, 2009. Other
common names
In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...
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 tigrinum'').
Distribution and habitat
The tawny nurse shark is widely distributed in the Indo-Pacific region. In the Indian Ocean, it is found from
KwaZulu-Natal,
South Africa northward to the
Red Sea,
Persian Gulf and
India, including
Madagascar,
Mauritius, the
Chagos Archipelago, the
Seychelles
Seychelles (, ; ), officially the Republic of Seychelles (french: link=no, République des Seychelles; Creole: ''La Repiblik Sesel''), is an archipelagic state consisting of 115 islands in the Indian Ocean. Its capital and largest city, ...
, and the
Maldives
Maldives (, ; dv, ދިވެހިރާއްޖެ, translit=Dhivehi Raajje, ), officially the Republic of Maldives ( dv, ދިވެހިރާއްޖޭގެ ޖުމްހޫރިއްޔާ, translit=Dhivehi Raajjeyge Jumhooriyyaa, label=none, ), is an archipela ...
. 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
The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages.
The sub-epoch lasted from 23.03 ± 0.05 Ma to 15.97 ± 0.05 Ma (million years ago). It was prece ...
(23–16
Ma). The presence of these fossils indicates that the range of the tawny nurse shark once extended to the tropical
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth#Surface, Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Afr ...
, prior to the formation of the
Isthmus of Panama
The Isthmus of Panama ( es, Istmo de Panamá), 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 countr ...
.
An inshore species, the tawny nurse shark inhabits
continental
Continental may refer to:
Places
* Continent, the major landmasses of Earth
* Continental, Arizona, a small community in Pima County, Arizona, US
* Continental, Ohio, a small town in Putnam County, US
Arts and entertainment
* ''Continental'' ( ...
and insular shelves over sandy flats or beds of
seagrass
Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families ( Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the ...
, as well as along the outer edges of
coral or
rocky reef
A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic processes—deposition (geology), deposition of ...
s. This shark may be found from the
surf zone
As ocean surface waves approach shore, they get taller and break, forming the foamy, bubbly surface called ''surf''. The region of breaking waves defines the surf zone, or breaker zone. After breaking in the surf zone, the waves (now reduced i ...
, often in water barely deep enough to cover its body, to a maximum depth of on coral reefs; it is most common at a depth of . Young sharks are generally found in the shallow areas of
lagoon
A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'' ...
s, while adults may be encountered across a variety of habitats.
Description
The tawny nurse shark grows to a maximum length of .
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
spiracles behind. There are a pair of long, slender
barbels
In fish anatomy and turtle anatomy, a barbel is a slender, whiskerlike sensory organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, the hagfish, the sturgeon, the zebrafish, the black dragonfish and some ...
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 slits 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
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as s ...
is even with or somewhat behind the origin of the second dorsal fin. The
caudal fin
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as s ...
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 long adult male with both a missing dorsal fin and partial
albinism
Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and pink or blue eyes. Individuals with the condition are referred to as albino.
Varied use and interpretation of the term ...
(in the form of white body color with gray-brown eyes) was captured off
Wakayama Prefecture
is a prefecture of Japan located in the Kansai region of Honshu. Wakayama Prefecture has a population of 944,320 () and has a geographic area of . Wakayama Prefecture borders Osaka Prefecture to the north, and Mie Prefecture and Nara 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
Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
.
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 shark
The sicklefin lemon shark (''Negaprion acutidens'') or sharptooth lemon shark is a species of requiem shark belonging to the family Carcharhinidae, widely distributed in the tropical waters of the Indo-Pacific. It is closely related to the bette ...
(''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
The bull shark (''Carcharhinus leucas''), also known as the Zambezi shark (informally zambi) in Africa and Lake Nicaragua shark in Nicaragua, is a species of requiem shark commonly found worldwide in warm, shallow waters along coasts and in ri ...
s (''Carcharhinus leucas'') and
great hammerhead
The great hammerhead (''Sphyrna mokarran'') or great hammerhead shark is the largest species of hammerhead shark, belonging to the family Sphyrnidae, attaining an average length of and reaching a maximum length of . It is found in tropical and w ...
s (''Sphyrna mokarran''), while the related nurse shark has been known to fall prey to
tiger sharks (''Galeocerdo cuvier'') and
lemon sharks (''Negaprion brevirostris'').
Known
parasites
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
of this species include five species of
tapeworms in the genus ''Pedibothrium'', which infest the shark's
spiral intestine.
Feeding
The tawny nurse shark may be one of the few fishes specializing in preying on octopus. Other known food items include
corals,
sea urchins,
crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s (e.g.
crab
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...
s and
lobsters),
squid, small fishes (e.g.
surgeonfish
Acanthuridae are the family of surgeonfishes, tangs, and unicornfishes. The family includes about 86 extant species of marine fish living in tropical seas, usually around coral reefs. Many of the species are brightly colored and popular in a ...
,
queenfish
The queenfish (''Seriphus politus'') is a species of fish in the family Sciaenidae, the drums and croakers. It is native to the eastern Pacific Ocean, where it occurs along the North American coastline from Oregon to Baja California; it has been ...
, and
rabbitfish
Rabbitfishes or spinefoots are perciform fishes in the family Siganidae. The 29 species are in a single genus, ''Siganus''. In some now obsolete classifications, the species having prominent face stripes—colloquially called foxfaces– ...
), 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.
Life history
Mating in the tawny nurse shark is known to occur from July to August off Madagascar.
Adult females have one functional
ovary
The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...
and two functional uteruses. The mode of reproduction is aplacental viviparity, meaning that the
embryos 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
Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...
. 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
The Lamniformes (, from Greek ''lamna'' "fish of prey") are an order of sharks commonly known as mackerel sharks (which may also refer specifically to the family Lamnidae). It includes some of the most familiar species of sharks, such as the gre ...
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 , with the discrepancy possibly reflecting geographic variation. Although females release up to four
fertilized
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proc ...
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 is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definitio ...
at a length of , and females at a length of .
Human interactions
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.
An Australian woman was bitten while hand feeding them in 2018.
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 (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...
. This shark is caught using demersal
trawls, floating and fixed bottom
gill net
Gillnetting is a fishing method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is ...
s, 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 is a traditional soup or stewed dish served in parts of China, Taiwan, and Southeast Asia. The shark fins provide texture, while the taste comes from the other soup ingredients. It is commonly served at special occasions such as ...
, and the
offal
Offal (), also called variety meats, pluck or organ meats, is the organs of a butchered animal. The word does not refer to a particular list of edible organs, which varies by culture and region, but usually excludes muscle. Offal may also refe ...
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 (making the tawny shark one of the few species of sharks to produce a noise);whether this is a deliberate defensive behavior is uncertain.
The
International Union for Conservation of Nature
The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of nat ...
(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
Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term ap ...
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
A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...
, as there it is not targeted by fisheries.
References
External links
''Nebrius ferrugineus'', Tawny nurse sharka
FishBase a
Florida Museum of Natural History Ichthyology Department*
''Debris ferrugineus'' @ fishesofaustralia.net.au
{{Taxonbar, from=Q751258
tawny nurse shark
Ovoviviparous fish
Marine fauna of East Africa
Fish of South Asia
Fish of the Red Sea
Fish of Oceania
Paleocene sharks
Paleogene sharks
Neogene sharks
Quaternary sharks
Danian first appearances
Vulnerable fauna of Asia
Vulnerable fauna of Oceania
tawny nurse shark
Taxa named by René Lesson
Extant Danian first appearances