Speartooth shark
Encyclopedia
The speartooth shark is an extremely rare species
of requiem shark
, family
Carcharhinidae. Only immature specimens, which inhabit the tidal
reaches of large tropical rivers in northern Australia
and New Guinea
, are known. It is exclusively found in fast-moving, highly turbid waters over a wide range of salinities
. This robustly built, gray-colored shark is characterized by a short and broad snout, tiny eyes, a relatively large second dorsal fin
, and a black blotch beneath each pectoral fin near the tip. Another identifying trait are its teeth, which are large, triangular, and serrated in the upper jaw and narrow, spear-like, and serrated only near the tips in the lower jaw. Based on available specimens, adults probably grow to 2.5–3 m (8.2–9.8 ft) long.
Preying on demersal bony fishes and crustacean
s, the speartooth shark is adapted for hunting in near-complete darkness. It is not as active as other requiem shark
s, moving upstream and downstream with tidal
currents so as to save energy. Reproduction is viviparous with females forming a placenta
l connection to their young, though details are unknown. The speartooth shark is threatened by incidental capture
in commercial
and recreational fisheries
, as well as by habitat degradation. Given its small population, restricted range, and stringent habitat
requirements, this species is highly susceptible to these pressures and has been listed as Endangered by the International Union for Conservation of Nature (IUCN).
and Jakob Henle
originally described the speartooth shark as Carcharias (Prionodon) glyphis, in their 1839–41 Systematische Beschreibung der Plagiostomen. They based their account on a stuffed
juvenile female 1 m (3.3 ft) long, of unknown origin (possibly the Indian Ocean
or the South China Sea
). In 1843, Swiss-American zoologist Louis Agassiz
proposed the new genus Glyphis for this species and a fossil
relative from Britain
, G. hastalis. However, the use of Glyphis to encompass the river sharks did not gain wide acceptance until Jack Garrick's 1982 revision of Carcharhinus
.
Müller and Henle's type specimen remained the sole known record of the speartooth shark until specimens of the "Bizant river shark" (Glyphis sp. A) were caught in Australia in 1982. Subsequently work by Leonard Compagno
, William White, and Peter Last confirmed initial suspicions that "sp. A" was the same species as G. glyphis. Thus, in Australia this shark may also be referred to as the Bizant river shark or the Queensland river shark.
-lined tropical rivers in northern Australia and New Guinea, from the estuary
to hundreds of kilometers upstream; there is a single possible record from the South China Sea. In Queensland
, it occurs in the Wenlock, Ducie
, and Bizant Rivers, and perhaps also the Normanby
, Hey, and Embly Rivers. In Northern Territory
, it is known from the Adelaide River
and the Alligator Rivers
. The river sharks in the Ord River
of Western Australia
may also be of this species. In New Guinea, this species has been reported from near Port Romilly and in the Fly River
.
Newborn to subadult speartooth sharks exclusively inhabit areas with fast tidal
currents and muddy bottoms; the flowing water produces heavy turbidity
, such as that <1% of sunlight penetrates beyond a depth of 1 m (3.3 ft). The salinity
level of these waters range from nearly fresh
(0.8 ppt) to nearly marine
(28 ppt), and temperatures range from 25 to 33 °C (77 to 91.4 F). Younger sharks are generally found further upstream than older ones. A study that tracked three individuals in the Adelaide River reported that they moved upstream with the flooding tide and downstream with the ebbing tide, averaging 10–12 km (6.2–7.5 mi) each way. The average swimming depth was determined for one individual to be 7.7 m (25.3 ft), in the middle of the water column. The range and habitat preferences of adult sharks are uncertain as none are known to have been captured; inshore marine waters are a reasonable possibility but have yet to be confirmed despite extensive surveys. There is no evidence of segregation by sex.
s (protective third eyelids). The sizable, arched mouth has very short furrows at the corners. There are 26–29 upper and 27–29 lower tooth rows. The teeth are tall and upright; those in the upper jaw are wide and triangular with serrated edges, while those in the lower jaw are narrow and spear-like with serrations only near the tip, and tiny cusplets at the base in very young individuals. There are five pairs of gill slit
s, with the first pair longer than the others.
The large pectoral fins have strongly convex leading and concave trailing margins, and blunt tips. The pelvic fins are triangular with nearly straight margins. The first dorsal fin
originates over the pectoral fin insertions, and is broadly triangular with a narrow apex and a concave trailing margin. The second dorsal fin
measures about 67–77% as tall as the first and is similar in shape; there is no midline ridge between the dorsal fins. The anal fin is almost as large as the second dorsal fin and lies slightly behind; it has a deep notch in the posterior margin. The caudal fin is asymmetrical; the lower lobe is narrow and well-developed, while the upper lobe has a gently convex upper margin and a prominent notch in the ventral margin near the tip. The body is covered by small, overlapping oval-shaped dermal denticles bearing 3 or 5 horizontal ridges leading to marginal teeth. This species is plain slate-gray above, including the upper surfaces of the pectoral and pelvic fins, and the caudal fin; the underside is white. The boundary between dark and light runs through the bottom rim of the eye, through the gill slits, over the flank well above the pelvic fins, and onto the upper caudal fin lobe. The fins darken towards the posterior margins, forming a black edge on the upper caudal fin lobe; each pectoral fin also has a black blotch underneath, near the tip. The eyes are ringed in white.
suggest that this shark relies more on electroreception
than sight to hunt, while the large second dorsal fin enhances its ability to maneuver at slow speeds in fast currents. It has slender teeth adept for catching bony fishes and crustacean
s, mostly on or near the bottom. Known prey include Macrobrachium
prawn
s, Taenoides or Trypauchen burrowing gobies
, ariid
catfish
, the threadfin
Polydactylus macrochir, the gudgeon
Prionobutis microps, the benthic croaker
Nibea squamosa and the bream Nematalosa erebi. As in other requiem sharks, the speartooth shark is viviparous: when the developing embryo
exhausts its supply of yolk, the yolk sac
develops into a placenta
l connection through which the mother delivers nourishment. Birthing seems to occur from October to December, near the end of the dry season
, with newborns measuring around 50–59 cm (19.7–23.2 in) long. The growth rate of young sharks is probably around 19 cm (7.5 in) per year.
by commercial fisheries
using gillnet
s and longlines, such as the barramundi
(Lates calcarifer) gillnet fishery in Queensland (barramundi fisheries in New South Wales have been prohibited from rivers occupied by this species since 2005). Significant numbers are also taken by recreational anglers
and bow fishers. Captured sharks might be eaten, used to bait crab pots, or discarded on land. Habitat degradation represents a third threat to the speartooth shark: the Fly River has been severely affected by pollutants
from mining activities, while proposed mining and dredging projects in the Port Musgrave
area and uranium
mining in Kakadu National Park
are also of concern.
The range of conservation threats faced by the speartooth shark, coupled with its small population and restricted range and habitat
preferences, have led the International Union for Conservation of Nature (IUCN) to assess it as Endangered. Furthermore, in Australia it has been listed as Critically Endangered on the 1999 Commonwealth Environment Protection and Biodiversity Conservation Act, though this is of minimal effect as Commonwealth protection does not apply until a distance of three nautical mile
s from the coast, likely outside the range of this shark. It has also been listed as Vulnerable on the 2000 Territory Parks and Wildlife Conservation Act, though a management plan has yet to be enacted. Sharks in the Kakadu and Lakefield National Park
s are protected somewhat from habitat alteration, if not fishing.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of requiem shark
Requiem shark
Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...
, family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Carcharhinidae. Only immature specimens, which inhabit the tidal
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
reaches of large tropical rivers in northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and 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...
, are known. It is exclusively found in fast-moving, highly turbid waters over a wide range of salinities
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...
. This robustly built, gray-colored shark is characterized by a short and broad snout, tiny eyes, a relatively large second dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
, and a black blotch beneath each pectoral fin near the tip. Another identifying trait are its teeth, which are large, triangular, and serrated in the upper jaw and narrow, spear-like, and serrated only near the tips in the lower jaw. Based on available specimens, adults probably grow to 2.5–3 m (8.2–9.8 ft) long.
Preying on demersal bony fishes and crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, the speartooth shark is adapted for hunting in near-complete darkness. It is not as active as other requiem shark
Requiem shark
Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...
s, moving upstream and downstream with tidal
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
currents so as to save energy. Reproduction is viviparous with females forming a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection to their young, though details are unknown. The speartooth shark is threatened by incidental capture
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...
in commercial
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...
and recreational fisheries
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
, as well as by habitat degradation. Given its small population, restricted range, and stringent habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
requirements, this species is highly susceptible to these pressures and has been listed as Endangered by the International Union for Conservation of Nature (IUCN).
Taxonomy
German biologists Johannes MüllerJohannes Peter Müller
Johannes Peter Müller , was a German physiologist, comparative anatomist, and ichthyologist not only known for his discoveries but also for his ability to synthesize knowledge.-Early years and education:...
and Jakob Henle
Friedrich Gustav Jakob Henle
Friedrich Gustav Jakob Henle was a German physician, pathologist and anatomist. He is credited with the discovery of the loop of Henle in the kidney. His essay "On Miasma and Contagia" was an early argument for the germ theory of disease...
originally described the speartooth shark as Carcharias (Prionodon) glyphis, in their 1839–41 Systematische Beschreibung der Plagiostomen. They based their account on a stuffed
Taxidermy
Taxidermy is the act of mounting or reproducing dead animals for display or for other sources of study. Taxidermy can be done on all vertebrate species of animals, including mammals, birds, fish, reptiles, and amphibians...
juvenile female 1 m (3.3 ft) long, of unknown origin (possibly the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
or the South China Sea
South China Sea
The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Singapore and Malacca Straits to the Strait of Taiwan of around...
). In 1843, Swiss-American zoologist Louis Agassiz
Louis Agassiz
Jean Louis Rodolphe Agassiz was a Swiss paleontologist, glaciologist, geologist and a prominent innovator in the study of the Earth's natural history. He grew up in Switzerland and became a professor of natural history at University of Neuchâtel...
proposed the new genus Glyphis for this species and a fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
relative from Britain
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, G. hastalis. However, the use of Glyphis to encompass the river sharks did not gain wide acceptance until Jack Garrick's 1982 revision of Carcharhinus
Carcharhinus
Carcharhinus is the type genus of the requiem shark family, Carcharhinidae.- Species :* Carcharhinus acarenatus * Carcharhinus acronotus...
.
Müller and Henle's type specimen remained the sole known record of the speartooth shark until specimens of the "Bizant river shark" (Glyphis sp. A) were caught in Australia in 1982. Subsequently work 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,...
, William White, and Peter Last confirmed initial suspicions that "sp. A" was the same species as G. glyphis. Thus, in Australia this shark may also be referred to as the Bizant river shark or the Queensland river shark.
Distribution and habitat
The speartooth shark is found in a handful of large, mangroveMangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
-lined tropical rivers in northern Australia and New Guinea, from the estuary
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
to hundreds of kilometers upstream; there is a single possible record from the South China Sea. In 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...
, it occurs in the Wenlock, Ducie
Ducie River
The Ducie River is a river of the Cape York Peninsula in Far North Queensland, Australia. It rises in the Great Dividing Range, flows through stringybark woodlands, tropical savanna plains and wetlands, and enters the Gulf of Carpentaria on the western side of the peninsula at Port Musgrave just...
, and Bizant Rivers, and perhaps also the Normanby
Normanby River
The Normanby River is a major river in northern Queensland, located on the edge of the Wet Tropics and flowing in a generally north-northwestward direction through seasonally flooded savanna grassland to Princess Charlotte Bay about 150 kilometres from Cooktown....
, Hey, and Embly Rivers. In Northern Territory
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...
, it is known from the Adelaide River
Adelaide River
Adelaide River is a river in the Northern Territory of Australia. It starts in Litchfield National Park and flows generally northwards to Clarence Strait, being crossed by both the Stuart Highway and the Arnhem Highway...
and the Alligator Rivers
Alligator Rivers
The Alligator Rivers is the name of a region in the Arnhem Land region of the Northern Territory of Australia, containing three rivers the East, West and South Alligator River...
. The river sharks in the Ord River
Ord River
The Ord River is a 320-kilometre-long river in the Kimberley region of Western Australia. It was named in honour of Harry Ord, Governor of Western Australia from 1877 to 1880....
of Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
may also be of this species. In New Guinea, this species has been reported from near Port Romilly and in the Fly River
Fly River
The Fly at , is the second longest river, after the Sepik, in Papua New Guinea. The Fly is the largest river in Oceania, the largest in the world without a single dam in its catchment, and overall ranks as the twenty-fifth largest river in the world by volume of discharge...
.
Newborn to subadult speartooth sharks exclusively inhabit areas with fast tidal
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
currents and muddy bottoms; the flowing water produces heavy turbidity
Turbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
, such as that <1% of sunlight penetrates beyond a depth of 1 m (3.3 ft). The 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...
level of these waters range from nearly fresh
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
(0.8 ppt) to nearly marine
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
(28 ppt), and temperatures range from 25 to 33 °C (77 to 91.4 F). Younger sharks are generally found further upstream than older ones. A study that tracked three individuals in the Adelaide River reported that they moved upstream with the flooding tide and downstream with the ebbing tide, averaging 10–12 km (6.2–7.5 mi) each way. The average swimming depth was determined for one individual to be 7.7 m (25.3 ft), in the middle of the water column. The range and habitat preferences of adult sharks are uncertain as none are known to have been captured; inshore marine waters are a reasonable possibility but have yet to be confirmed despite extensive surveys. There is no evidence of segregation by sex.
Description
The largest known male and female speartooth sharks on record were 1.6 m (5.2 ft) and 1.8 m (5.9 ft) long respectively, suggesting an adult maximum length of 2.5–3 m (8.2–9.8 ft). The speartooth shark has a streamlined, rather robust body with a short, wide head. The snout is flattened, with large nostrils divided into incurrent and excurrent openings by large, triangular flaps of skin. The eyes are small and equipped with nictitating membraneNictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...
s (protective third eyelids). The sizable, arched mouth has very short furrows at the corners. There are 26–29 upper and 27–29 lower tooth rows. The teeth are tall and upright; those in the upper jaw are wide and triangular with serrated edges, while those in the lower jaw are narrow and spear-like with serrations only near the tip, and tiny cusplets at the base in very young individuals. There are five 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, with the first pair longer than the others.
The large pectoral fins have strongly convex leading and concave trailing margins, and blunt tips. The pelvic fins are triangular with nearly straight margins. The first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
originates over the pectoral fin insertions, and is broadly triangular with a narrow apex and a concave trailing margin. The second dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
measures about 67–77% as tall as the first and is similar in shape; there is no midline ridge between the dorsal fins. The anal fin is almost as large as the second dorsal fin and lies slightly behind; it has a deep notch in the posterior margin. The caudal fin is asymmetrical; the lower lobe is narrow and well-developed, while the upper lobe has a gently convex upper margin and a prominent notch in the ventral margin near the tip. The body is covered by small, overlapping oval-shaped dermal denticles bearing 3 or 5 horizontal ridges leading to marginal teeth. This species is plain slate-gray above, including the upper surfaces of the pectoral and pelvic fins, and the caudal fin; the underside is white. The boundary between dark and light runs through the bottom rim of the eye, through the gill slits, over the flank well above the pelvic fins, and onto the upper caudal fin lobe. The fins darken towards the posterior margins, forming a black edge on the upper caudal fin lobe; each pectoral fin also has a black blotch underneath, near the tip. The eyes are ringed in white.
Biology and ecology
The speartooth shark seems to be relatively sluggish in nature, moving with the tides so as to conserve energy. Its activity levels are unaffected by day or night, reflecting the constant darkness of its environment. Small eyes and abundant ampullae of LorenziniAmpullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...
suggest that this shark relies more on electroreception
Electroreception
Electroreception is the biological ability to perceive natural electrical stimuli. It has been observed only in aquatic or amphibious animals, since water is a much better conductor than air. Electroreception is used in electrolocation and for electrocommunication.- Overview :Electroreception is...
than sight to hunt, while the large second dorsal fin enhances its ability to maneuver at slow speeds in fast currents. It has slender teeth adept for catching bony fishes and crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, mostly on or near the bottom. Known prey include Macrobrachium
Macrobrachium
Macrobrachium is a genus of freshwater shrimp characterised by the extreme enlargement of the second pair of pereiopods, at least in the male...
prawn
Prawn
Prawns are decapod crustaceans of the sub-order Dendrobranchiata. There are 540 extant species, in seven families, and a fossil record extending back to the Devonian...
s, Taenoides or Trypauchen burrowing gobies
Goby
The gobies form the family Gobiidae, which is one of the largest families of fish, with more than 2,000 species in more than 200 genera. Most are relatively small, typically less than 10 cm in length...
, ariid
Ariidae
The Ariidae or ariid catfish are a family of catfish that mainly live in marine waters with many freshwater and brackish water species. They are found worldwide in tropical to warm temperate zones.-Taxonomy:...
catfish
Catfish
Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...
, the threadfin
Threadfin
Threadfins are silvery grey perciform marine fish of the family Polynemidae. Found in tropical to subtropical waters throughout the world, the threadfin family contains nine genera and 33 species...
Polydactylus macrochir, the gudgeon
Gudgeon (fish)
Gudgeon is a common name for a number of small freshwater fishes of the families Cyprinidae, Eleotridae or Ptereleotridae. Most gudgeons are elongate, bottom-dwelling fish, many of which live in rapids and other fast moving water....
Prionobutis microps, the benthic croaker
Sciaenidae
Sciaenidae is a family of fish commonly called drums, croakers, or hardheads for the repetitive throbbing or drumming sounds they make...
Nibea squamosa and the bream Nematalosa erebi. As in other requiem sharks, the speartooth shark is viviparous: when the developing embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
exhausts its supply of yolk, the yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
develops into a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection through which the mother delivers nourishment. Birthing seems to occur from October to December, near the end of the dry season
Dry season
The dry season is a term commonly used when describing the weather in the tropics. The weather in the tropics is dominated by the tropical rain belt, which oscillates from the northern to the southern tropics over the course of the year...
, with newborns measuring around 50–59 cm (19.7–23.2 in) long. The growth rate of young sharks is probably around 19 cm (7.5 in) per year.
Human interactions
The speartooth shark is not known to pose a danger to humans. Extremely rare like other river sharks, its global population has been estimated to number no more than 2,500 mature individuals, with no more than 250 in any subpopulation. This species is caught incidentallyBycatch
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...
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...
using gillnet
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
s and longlines, such as the barramundi
Barramundi
The Barramundi , also known as Asian Seabass, is a species of catadromous fish in family Latidae of order Perciformes. The native species is widely distributed in the Indo-West Pacific region from the Persian Gulf, through Southeast Asia to Papua New Guinea and Northern Australia. Known in Thai...
(Lates calcarifer) gillnet fishery in Queensland (barramundi fisheries in New South Wales have been prohibited from rivers occupied by this species since 2005). Significant numbers are also taken by recreational anglers
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
and bow fishers. Captured sharks might be eaten, used to bait crab pots, or discarded on land. Habitat degradation represents a third threat to the speartooth shark: the Fly River has been severely affected by pollutants
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....
from mining activities, while proposed mining and dredging projects in the Port Musgrave
Port Musgrave
Port Musgrave is a shallow, almost enclosed, estuary, forming a bay on the western coast of the Cape York Peninsula in Far North Queensland, Australia. Two major rivers, the Wenlock and the Ducie discharge into it. The surrounding area is rich in freshwater swamps, while the estuary itself has...
area and uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
mining in Kakadu National Park
Kakadu National Park
Kakadu National Park is in the Northern Territory of Australia, 171 km southeast of Darwin.Kakadu National Park is located within the Alligator Rivers Region of the Northern Territory of Australia. It covers an area of , extending nearly 200 kilometres from north to south and over 100 kilometres...
are also of concern.
The range of conservation threats faced by the speartooth shark, coupled with its small population and restricted range and habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
preferences, have led the International Union for Conservation of Nature (IUCN) to assess it as Endangered. Furthermore, in Australia it has been listed as Critically Endangered on the 1999 Commonwealth Environment Protection and Biodiversity Conservation Act, though this is of minimal effect as Commonwealth protection does not apply until a distance of three nautical mile
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
s from the coast, likely outside the range of this shark. It has also been listed as Vulnerable on the 2000 Territory Parks and Wildlife Conservation Act, though a management plan has yet to be enacted. Sharks in the Kakadu and Lakefield National Park
Lakefield National Park
Lakefield is a national park in Queensland, Australia, 1,707 km northwest of Brisbane and 340 km north-west of Cairns by road, on Cape York Peninsula. At 5,370 km2 Lakefield is a national park in Queensland, Australia, 1,707 km northwest of Brisbane and 340 km north-west of...
s are protected somewhat from habitat alteration, if not fishing.