New Guinea river shark
Encyclopedia
The northern river shark or New Guinea river shark (Glyphis garricki) is a species
of requiem shark
, family
Carcharhinidae, found in scattered tidal river
s and associated coastal waters in northern Australia
and possibly Papua New Guinea
. This species inhabits areas with poor visibility, soft bottoms, and large tide
s, with immature sharks ranging into fresh
and brackish water
. It is similar to other river sharks in having a stocky gray body with a high back, tiny eyes, and broad fins. It measures up to 2.5 m (8.2 ft) long.
Northern river sharks are likely piscivorous. This species is viviparous, with females bearing litters of 9 young possibly every other year before the wet season
. Very rare and facing threats from commercial
and recreational fishing
, and perhaps also habitat degradation, this species has been assessed as Critically Endangered
by the International Union for Conservation of Nature (IUCN).
, were discovered by New Zealand
ichthyologist Jack Garrick, after whom the species would eventually be named. This shark was referred to as "Glyphis sp. C" until 2008, when it was formally described by Leonard Compagno
, William White, and Peter Last in a Commonwealth Scientific and Industrial Research Organisation
(CSIRO) paper. The type specimen is a female 67 cm (26.4 in) long, collected from the East Alligator River, Kakadu National Park
, Northern Territory
.
, the Ord River
, and Doctors Creek near Derby
in Western Australia
, the Adelaide
and Alligator Rivers
in Northern Australia, and possibly the Fly River
in Papua New Guinea. It inhabits large river
s, estuaries, and coastal bay
s, all of which are characterized by high turbidity
, silty or muddy bottoms, and large tides. Young and juvenile sharks are found in fresh, brackish, and salt water (salinity
ranging from 2 to 36 ppt), whereas adults have only been found in marine environments.
s. Each nostril
is divided into a very large incurrent opening and a small excurrent opening by a triangular skin flap. The sizable mouth is broadly arched, with short furrows at the corners. There are 31–34 tooth rows in the upper jaw and 30–35 tooth rows in the lower jaw; the upper teeth are upright and triangular with serrated edges, while the lower teeth are narrower and straight to slightly curved. In the largest individuals, the first few lower teeth from the jaw median are hastate (spear-shaped) with serrations near the tip.
The pectoral fins are large and broad, with gently backward-curving margins and pointed tips. The pelvic fins are triangular with nearly straight trailing margins. The first dorsal fin
is long-based and triangular, with the apex almost forming a right angle; the second dorsal fin is some two-thirds as high as the first. The origin of the first dorsal fin lies over the pectoral fin insertions, while that of second dorsal fin lies over the pelvic fin rear tips. There is no ridge between the dorsal fins. The anal fin is smaller than the second dorsal fin and has a strong notch in the rear margin. The caudal fin has a strong lower lobe and a long, narrow upper lobe with a ventral notch near the tip. The dermal denticles are small, oval, and overlapping, bearing three horizontal ridges leading to marginal teeth. This shark is steel-gray above and white below; the color transition is sharp, located well below the eye, and becomes jagged on the sides of the trunk. The anal and caudal fins become dusky or black towards the trailing margins and tips. The maximum known length is 2.5 m (8.2 ft). This species differs from the speartooth shark
(G. glyphis) in several morphological
and meristic characters, including having fewer vertebrae (137–151 versus 213–222) and a lower, jagged gray-white color boundary.
, the northern river shark seems to be adapted
for hunting fish
in conditions of poor visibility. In Doctors Creek, there is evidence that sharks may move to and from favored feeding areas with the tide. Like other requiem sharks, this species is viviparous with the developing embryo
s forming a placenta
l connection to their mother after exhausting their supply of yolk. Females give birth around October, before the start of the wet season
, on possibly a biennial cycle. One female examined contained nine fetus
es. The young are born at under 67 cm (26.4 in) long; males mature
between lengths of 1.2 and 1.4 m (3.9 and 4.6 ft), while females mature between lengths of 1.4 and 1.7 m (4.6 and 5.6 ft).
s, as well as by recreational fishers
; habitat degradation may pose a further threat to its survival. Because of its low natural abundance, limited distribution, stringent habitat requirements, and susceptibility to various human-caused threats, the International Union for Conservation of Nature (IUCN) has assessed the northern river shark as Critically Endangered
. It has also been listed as Endangered on the 1999 Commonwealth Environment Protection and Biodiversity Conservation Act, and on the 2000 Territory Parks and Wildlife Conservation Act. Kakadu National Park may be an important protected area for this species.
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, found in scattered tidal river
Tidal river
A tidal river is a river, or more typically a stretch of a river, whose flow and level is influenced by tides. An example of a tidal river is the portion of the Connecticut River flowing from Windsor Locks, Connecticut, to the Atlantic Ocean. The Brisbane River, which flows into the Pacific Ocean...
s and associated coastal waters 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 possibly Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
. This species inhabits areas with poor visibility, soft bottoms, and large tide
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....
s, with immature sharks ranging into fresh
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
and brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
. It is similar to other river sharks in having a stocky gray body with a high back, tiny eyes, and broad fins. It measures up to 2.5 m (8.2 ft) long.
Northern river sharks are likely piscivorous. This species is viviparous, with females bearing litters of 9 young possibly every other year before the wet season
Wet season
The the wet season, or rainy season, is the time of year, covering one or more months, when most of the average annual rainfall in a region occurs. The term green season is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the...
. Very rare and facing threats from 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 fishing
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 perhaps also habitat degradation, this species has been assessed as Critically Endangered
Critically Endangered
Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species' numbers have decreased, or will decrease, by 80% within three generations....
by the International Union for Conservation of Nature (IUCN).
Taxonomy
The first known specimens of the northern river shark, two newborn males from Papua New GuineaPapua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
, were discovered by New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
ichthyologist Jack Garrick, after whom the species would eventually be named. This shark was referred to as "Glyphis sp. C" until 2008, when it was formally described 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 in a Commonwealth Scientific and Industrial Research Organisation
Commonwealth Scientific and Industrial Research Organisation
The Commonwealth Scientific and Industrial Research Organisation is the national government body for scientific research in Australia...
(CSIRO) paper. The type specimen is a female 67 cm (26.4 in) long, collected from the East Alligator River, 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...
, 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...
.
Distribution and habitat
The northern river shark has been reported from King SoundKing Sound
King Sound is a large gulf in northern Western Australia. It expands from the mouth of the Fitzroy River, one of Australia's largest watercourses, and opens to the Indian Ocean. It is about 120 km long, and averages about 50 km in width. The port town of Derby lies near the mouth of the...
, 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....
, and Doctors Creek near Derby
Derby, Western Australia
Derby is a town in the Kimberley region of Western Australia. At the 2006 census, Derby had a population of 3,093. Along with Broome and Kununurra, it is one of only three towns in the Kimberley to have a population over 2,000...
in 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...
, the Adelaide
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 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...
in Northern Australia, and possibly 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...
in Papua New Guinea. It inhabits large river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
s, estuaries, and coastal bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s, all of which are characterized by high 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....
, silty or muddy bottoms, and large tides. Young and juvenile sharks are found in fresh, brackish, and salt water (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...
ranging from 2 to 36 ppt), whereas adults have only been found in marine environments.
Description
Like other members of its genus, the northern river shark has a stocky body with a high back. The head is wide and flattened, with a broadly rounded snout and minute eyes 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. Each nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
is divided into a very large incurrent opening and a small excurrent opening by a triangular skin flap. The sizable mouth is broadly arched, with short furrows at the corners. There are 31–34 tooth rows in the upper jaw and 30–35 tooth rows in the lower jaw; the upper teeth are upright and triangular with serrated edges, while the lower teeth are narrower and straight to slightly curved. In the largest individuals, the first few lower teeth from the jaw median are hastate (spear-shaped) with serrations near the tip.
The pectoral fins are large and broad, with gently backward-curving margins and pointed tips. The pelvic fins are triangular with nearly straight trailing 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...
is long-based and triangular, with the apex almost forming a right angle; the second dorsal fin is some two-thirds as high as the first. The origin of the first dorsal fin lies over the pectoral fin insertions, while that of second dorsal fin lies over the pelvic fin rear tips. There is no ridge between the dorsal fins. The anal fin is smaller than the second dorsal fin and has a strong notch in the rear margin. The caudal fin has a strong lower lobe and a long, narrow upper lobe with a ventral notch near the tip. The dermal denticles are small, oval, and overlapping, bearing three horizontal ridges leading to marginal teeth. This shark is steel-gray above and white below; the color transition is sharp, located well below the eye, and becomes jagged on the sides of the trunk. The anal and caudal fins become dusky or black towards the trailing margins and tips. The maximum known length is 2.5 m (8.2 ft). This species differs from the speartooth shark
Speartooth shark
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...
(G. glyphis) in several morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
and meristic characters, including having fewer vertebrae (137–151 versus 213–222) and a lower, jagged gray-white color boundary.
Biology and ecology
With its slender teeth, small eyes, and high density of 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...
, the northern river shark seems to be adapted
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
for hunting fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
in conditions of poor visibility. In Doctors Creek, there is evidence that sharks may move to and from favored feeding areas with the tide. Like other requiem sharks, this species is viviparous with the developing embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s 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 mother after exhausting their supply of yolk. Females give birth around October, before the start of the wet season
Wet season
The the wet season, or rainy season, is the time of year, covering one or more months, when most of the average annual rainfall in a region occurs. The term green season is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the...
, on possibly a biennial cycle. One female examined contained nine fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
es. The young are born at under 67 cm (26.4 in) long; males mature
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...
between lengths of 1.2 and 1.4 m (3.9 and 4.6 ft), while females mature between lengths of 1.4 and 1.7 m (4.6 and 5.6 ft).
Human interactions
The northern river shark appears to be extremely rare, though more subpopulations may remain to be discovered in Australia and Papua New Guinea. Based on present information, no more than 250 mature individuals are estimated to exist in the wild, with no more than 50 in any particular subpopulation. This species is caught legally and illegally by commercial fisheries using longlines and gillnetGillnet
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, as well as by recreational fishers
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....
; habitat degradation may pose a further threat to its survival. Because of its low natural abundance, limited distribution, stringent habitat requirements, and susceptibility to various human-caused threats, the International Union for Conservation of Nature (IUCN) has assessed the northern river shark as Critically Endangered
Critically Endangered
Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species' numbers have decreased, or will decrease, by 80% within three generations....
. It has also been listed as Endangered on the 1999 Commonwealth Environment Protection and Biodiversity Conservation Act, and on the 2000 Territory Parks and Wildlife Conservation Act. Kakadu National Park may be an important protected area for this species.