The nervous shark (''Carcharhinus cautus'') is a
species
In biology, a species is the basic unit of 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 the appropriate s ...
of
requiem shark
Requiem sharks are sharks of the family Carcharhinidae in the order Carcharhiniformes. They are migratory, live-bearing sharks of warm seas (sometimes of brackish or fresh water) and include such species as the tiger shark, bull shark, le ...
, and part of the
family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
Carcharhinidae, so named because of its timid behavior in regard to humans. It is common in shallow, coastal waters off northern
Australia,
Papua New Guinea
Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...
, and the
Solomon Islands
Solomon Islands is an island country consisting of six major islands and over 900 smaller islands in Oceania, to the east of Papua New Guinea and north-west of Vanuatu. It has a land area of , and a population of approx. 700,000. Its capit ...
. A small brownish or grayish shark typically measuring long, this species has a short, blunt snout, oval eyes, and a relatively large second
dorsal fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...
. The leading margins of most fins are finely edged with black, and the lower
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 ...
lobe is black-tipped.
Small
bony fishes are the main
prey
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...
of the nervous shark, while
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 can ...
s,
molluscs, and
snake
Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...
s may also be eaten. It is
viviparous
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...
, with the developing
embryos nourished through a
placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
l connection. The details of its life history seem to vary depending on
latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
—for example, the timing of the
breeding season and the length of the
gestation period. Females produce litters of one to six young either annually or biennially. The harmless nervous shark is
caught incidentally by coastal
gillnet fisheries and perhaps also by line and
trawl
Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch different speci ...
fisheries. 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 been listed under
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 ...
.
Taxonomy and phylogeny
Australian
ichthyologist Gilbert Percy Whitley
Gilbert Percy Whitley (9 June 1903 – 18 July 1975) 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 ...
originally described the nervous shark as a
subspecies of ''Galeolamna greyi'' (a
junior synonym of ''Carcharhinus obscurus'', the
dusky shark), in a 1945 issue of the
scientific journal ''Australian Zoologist''. He gave it the name ''cauta'', meaning "cautious" in
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
, because of its skittish demeanor when confronted by people.
Later authors have recognized this shark as a distinct species, placed in the genus ''
Carcharhinus''. The
type specimen
In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...
consists of the preserved skin and teeth of a long female caught in
Shark Bay,
Western Australia
Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
.
Based on
morphology
Morphology, from the Greek and meaning "study of shape", may refer to:
Disciplines
* Morphology (archaeology), study of the shapes or forms of artifacts
* Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
,
Jack Garrick
John Andrew Frank "Jack" Garrick (1928 – August 30, 2018) was a New Zealand ichthyologist. He specialized in elasmobranchs and published many books and articles about shark and ray biology. In 1982, he published a thorough taxonomy on sharks of ...
suggested in 1982 that the nervous shark is closely related to the
blacktip reef shark (''C. melanopterus'').
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 Organ ...
in 1988 tentatively grouped these two species with the
blacknose shark
The blacknose shark (''Carcharhinus acronotus'') is a species of requiem shark, belonging to the family Carcharhinidae, common in the tropical and subtropical waters of the western Atlantic Ocean. This species generally inhabits coastal seagrass ...
(''C. acronotus''), the
copper shark
The copper shark (''Carcharhinus brachyurus''), bronze whaler, or narrowtooth shark, is a species of requiem shark, family Carcharhinidae, and the only member of its genus found mostly at temperate latitudes. It is distributed in a number of sepa ...
(''C. brachyurus''), the
silky shark
The silky shark (''Carcharhinus falciformis''), also known by numerous names such as blackspot shark, gray whaler shark, olive shark, ridgeback shark, sickle shark, sickle-shaped shark and sickle silk shark, is a species of requiem shark, in the ...
(''C. falciformis''), and the
night shark
The night shark (''Carcharhinus signatus'') is a species of requiem shark, in the family Carcharhinidae, found in the temperate and tropical waters of the Atlantic Ocean. An inhabitant of the outer continental shelf and upper continental slope ...
(''C. signatus'').
The close relationship between the nervous and blacktip reef sharks was upheld in a 1992
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
study by Shane Lavery, based on
allozymes,
and again in a 2011 study by Ximena Vélez-Zuazoa and Ingi Agnarsson, based on
nuclear
Nuclear may refer to:
Physics
Relating to the nucleus of the atom:
* Nuclear engineering
*Nuclear physics
*Nuclear power
*Nuclear reactor
*Nuclear weapon
*Nuclear medicine
*Radiation therapy
*Nuclear warfare
Mathematics
*Nuclear space
*Nuclear ...
and
mitochondrial gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
s.
Description
The nervous shark has a rather stout, spindle-shaped body and a short, broadly rounded snout. The anterior margin of each nostril is extended into a slender nipple-shaped lobe. The moderately large eyes are horizontally oval in shape and equipped with
nictitating membranes. The mouth lacks conspicuous furrows at the corners and contains 25–30 upper and 23–28 lower tooth rows. The upper teeth are narrow and angled, with coarsely serrated edges. The lower teeth are more slender and upright in shape, and have finer serrations. The five pairs of
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 and rays, as well as deep-branching vertebrates such as lampreys. In con ...
s are medium in length.
The
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 ...
s are moderately long, narrow, and pointed. The first
dorsal fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...
originates over the free rear tips of the pectoral fins; it is large and falcate (sickle-shaped) with a pointed apex. The second dorsal fin is positioned opposite the
anal fin and is relatively large and high. There is no ridge between the dorsal fins. A crescent-shaped notch is present on the
caudal peduncle
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 see ...
just before the upper
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 ...
origin. The caudal fin is asymmetrical, with a strong lower lobe and a longer upper lobe with a ventral notch near the tip.
The
dermal denticles are overlapping and bear three horizontal ridges (five in larger individuals) leading to marginal teeth.
This species is bronze to gray above and white below, with a white stripe on the flank. A thin black line runs along the leading margins of the dorsal fins, pectoral fins, and the upper caudal fin lobe, as well as the caudal fin trailing margin; the lower caudal fin lobe and sometimes the pectoral fins are also tipped in black.
The nervous shark typically reaches in length and may grow up to long.
Females attain larger sizes than males.
Distribution and habitat
The nervous shark is found over
continental and insular shelves off northern Australia from Shark Bay in the west to
Moreton Bay
Moreton Bay is a bay located on the eastern coast of Australia from central Brisbane, Queensland. It is one of Queensland's most important coastal resources. The waters of Moreton Bay are a popular destination for recreational anglers and are ...
in the east, as well as off
Papua New Guinea
Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...
and around the
Solomon Islands
Solomon Islands is an island country consisting of six major islands and over 900 smaller islands in Oceania, to the east of Papua New Guinea and north-west of Vanuatu. It has a land area of , and a population of approx. 700,000. Its capit ...
.
It is among the most common sharks in
Darwin Harbor, the
Gulf of Carpentaria, and Shark Bay.
This species generally inhabits shallow
inshore waters, to a depth of at least .
It seems to particularly favor
mangrove
A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in severa ...
-lined areas with sandy-muddy bottoms and avoids areas with dense
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 or ...
cover.
Biology and ecology
![Cerberus schneiderii](https://upload.wikimedia.org/wikipedia/commons/1/1e/Cerberus_schneiderii.jpg)
The diet of the nervous shark consists mainly of small
teleost fishes (including
silversides,
smelt-whitings,
wrasse
The wrasses are a family, Labridae, of marine fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 81 genera, which are divided into 9 subgroups or tribes.
They are typically small, most of them le ...
s, and
grunters).
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 can ...
s (including
prawn
Prawn is a common name for small aquatic crustaceans with an exoskeleton and ten legs (which is a member of the order decapoda), some of which can be eaten.
The term "prawn"Mortenson, Philip B (2010''This is not a weasel: a close look at nature' ...
s,
crabs, and
mantis shrimps) and
molluscs (predominantly
cephalopods but also
bivalves and
gastropods) constitute secondary food sources.
This shark is also known to occasionally prey on the semiaquatic
snake
Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...
s ''
Cerberus rynchops
''Cerberus rynchops'', also known as the New Guinea bockadam, South Asian bockadam, bockadam snake, or dog-faced water snake, is a mildly venomous species of a snake in the family Homalopsidae. It is native to coastal waters of South and South ...
'' and ''
Fordonia leucobalia''.
A known
parasite
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 ...
of the nervous shark is the
myxosporea
Myxosporea is a class of microscopic parasites, belonging to the Myxozoa clade within Cnidaria. They have a complex life cycle which comprises vegetative forms in two hosts, an aquatic invertebrate (generally an annelid but sometimes a bryozoa ...
n ''Kudoa carcharhini''.
Like other requiem sharks, the nervous shark is
viviparous
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...
: once the
embryos exhaust their initial supply of
yolk
Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example ...
, they are provisioned by the mother through a
placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mate ...
l connection formed from the depleted
yolk sac
The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac'' is ...
. Adult females have a single functional
ovary, on the right, and two functional
uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
es. The male bites at the sides of the female as a prelude to mating. After mating, the female stores the
sperm for approximately four weeks prior to
fertilization
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. Proce ...
. In Darwin Harbor, mating occurs from January to March and birthing occurs in October and November following a
gestation period of eight to nine months. In Shark Bay, mating occurs from late October to early November and birthing occurs around the same time the following year, following a gestation period of 11 months; this slower development likely reflects the cooler temperatures of Shark Bay.
Females produce litters on an annual cycle in Darwin Harbor and on a biennial cycle in Shark Bay. The litter size ranges from one to six and is not correlated with the size of the female. The newborns are relatively large, measuring long, and are birthed in shallow nursery areas such as Herald Bight in Shark Bay. The juvenile growth rate is high for a shark; males and females
mature sexually at around , respectively, in Darwin Harbour, and , respectively, in Shark Bay. The age at maturity is around four years for males and six years for females; the
maximum lifespan is at least 12 years for males and 16 years for females.
Human interactions
Shy and difficult to approach, the nervous shark is harmless to humans.
It is occasionally marketed for food.
This species is susceptible to being
caught incidentally in coastal
gillnets, such as the
barramundi
The barramundi (''Lates calcarifer'') or Asian sea bass, is a species of catadromous fish in the family Latidae of the order Perciformes. The species is widely distributed in the Indo-West Pacific, spanning the waters of the Middle East, Sout ...
(''Lates calcarifer'') gillnet fishery operating off northern Australia. It may also be caught on line gear and in prawn
trawl
Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch different speci ...
s. The Australian nervous shark population does not appear to be threatened by fishing activities, and there 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 it as
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 ...
.
References
External links
''Carcharhinus cautus'', Nervous sharka
FishBaseCarcharhinus cautus at www.shark-references.com
{{Taxonbar, from=Q1978204
nervous shark
Marine fish of Northern Australia
Fauna of Papua New Guinea
Fauna of the Solomon Islands
nervous shark