The Australian weasel shark (''Hemigaleus australiensis'') is an uncommon

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 ...

ground shark Carcharhiniformes , the ground sharks, are the largest order of sharks, with over 270 species. They include a number of common types, such as catsharks, swellsharks, and the sandbar shark. Members of this order are characterized by the presence ...

in 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 ...

Hemigaleidae. It inhabits shallow waters off northern Australia to a depth of ; smaller sharks frequent sand 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 or ...

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

and shift to

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. C ...

s as they grow older. A slim, drab species reaching a length of , it has sickle-shaped fins with dark tips on the 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 ...

and

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 ...

upper lobe. Its upper teeth are broad with strong serrations only on the trailing edge. The lateral line along each side is prominent and exhibits a downward curve below the second dorsal fin. Feeding almost exclusively on octopuses and other cephalopods, the Australian weasel shark mostly hunts near the sea floor. 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 and born after a six-month gestation period. This species is

productive Productivity is the efficiency of production of goods or services expressed by some measure. Measurements of productivity are often expressed as a ratio of an aggregate output to a single input or an aggregate input used in a production proces ...

for a shark, with females bearing litters of 1–19 pups usually twice per year. The Australian weasel shark is caught by

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 ...

and to a lesser extent gillnet and longline fisheries, though not in such numbers that its population is threatened. Thus, it has been listed 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 ...

by 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).

Taxonomy

Originally regarded as

conspecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...

with the sicklefin weasel shark (''H. microstoma''), the Australian weasel shark was first documented as a potentially distinct species by John Stevens and Glen Cuthbert in 1983. Its scientific description was authored by William White, Peter Last, and

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 a 2005 volume of the scientific journal ''

Zootaxa ''Zootaxa'' is a peer-reviewed scientific mega journal for animal taxonomists. It is published by Magnolia Press (Auckland, New Zealand). The journal was established by Zhi-Qiang Zhang in 2001 and new issues are published multiple times a week ...

''. They gave it the specific epithet ''australiensis'' on the basis of its range, and designated as 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 ...

an adult male long caught at a depth of off

Geraldton Geraldton ( Wajarri: ''Jambinu'', Wilunyu: ''Jambinbirri'') is a coastal city in the Mid West region of the Australian state of Western Australia, north of the state capital, Perth. At June 2018, Geraldton had an urban population of 37,648. ...

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 ...

Description

Reaching in length, the Australian weasel shark has a slender, spindle-shaped body and a moderately long head with a thick, rounded snout. The large, oval eyes possess nictitating membranes and have notched posterior rims. Tiny spiracles are located behind and above the eyes. The large nostrils are preceded by fairly long, triangular flaps of skin. The short, curved mouth bears prominent furrows at the corners. There are 28–30 upper and 46–52 lower

tooth row Sharks continually shed their teeth; some Carcharhiniformes shed approximately 35,000 teeth in a lifetime, replacing those that fall out. There are four basic types of shark teeth: dense flattened, needle-like, pointed lower with triangular up ...

s, which are not visible when the mouth is closed; the upper teeth are broad and angled with large serrations on the trailing edge only, whereas the lower teeth are thin and upright with smooth edges. There are five pairs of fairly short

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. All of the fins, particularly the narrow

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 falcate (sickle-shaped) to some degree. The medium-sized first

originates just behind the pectoral fin rear tips. The second dorsal fin is about two-thirds as tall as the first, and there is no midline ridge running between them. The pelvic fins are broad and slightly larger than the anal fin. The anal fin has a strong notch in the trailing margin and is positioned slightly behind the second dorsal fin. 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 ...

bears a crescent-shaped notch at the upper origin of the

. The asymmetrical caudal fin has a well-developed lower lobe and a long, narrow upper lobe with a ventral notch near the tip. The prominent lateral line curves downward below the second dorsal fin. The skin is densely covered by small, overlapping dermal denticles; each bears five horizontal ridges leading to marginal teeth. This species is light grey to bronze above, darkening at the tips of the second dorsal fin and upper caudal fin lobe (though this may be indistinct in larger sharks), and pale below. The underside is off-white, and the first dorsal fin has a pale trailing margin.

Distribution and habitat

The Australian weasel shark inhabits continental and insular shelves off northern Australia, from Geraldton in Western Australia to

Brunswick Heads Brunswick Heads is a small town on the north coast of New South Wales, Australia in Byron Shire. At the , the town had a population of 1,737 people. History Originally inhabited by people of the Bundjalung nation, the Brunswick River was c ...

New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...

. Additional records from

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 ...

are as yet unconfirmed. It seems to be naturally rather uncommon. This species tends to swim close to the sea floor and can be found from inshore waters down to deep. Juveniles and small adults are generally found in sandy areas with

cover, while large adults occur more around

Biology and ecology

The Australian weasel shark feeds predominantly on octopuses such as '' Callistoctopus'' spp., either swallowing them whole or removing the arms first. Octopuses become increasingly important to its diet with age, such that sharks over long eat almost nothing else; this increasing dietary specialisation is accompanied by a

shift toward coral reefs, which may serve to reduce competition between older and younger individuals. Bobtail squids represent a minor secondary food source, particularly for smaller sharks. In addition, other cephalopods,

mud lobster Thalassinidea is a former infraorder of decapod crustaceans that live in burrows in muddy bottoms of the world's oceans. In Australian English, the littoral thalassinidean '' Trypaea australiensis'' is referred to as the ''yabby'' (a term whic ...

s, crabs, and

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...

s are rarely consumed. This species probably hunts mostly at dawn and dusk; it typically seeks bottom-dwelling prey but will also rise into the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

if opportunity presents, such as during seasonal aggregations of broad squid (''Uroteuthis etheridgei''). 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 ...

s of the Australian weasel shark include the

tapeworm Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda (the other subclass is Cestodaria). Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Cesto ...

s '' Nybelinia mehlhorni'', '' Paraorygmatobothrium kirstenae'', and '' P. taylori'', and the copepods '' Perissopus dentatus'' and '' Pseudopandarus australis''. Like other members of its family, the Australian weasel shark is

with the developing embryos sustained through a

l connection with the mother. Mature females have a single functional ovary 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 gestation period is six months long and typically two litters are produced annually, one around February and the other around September. Litter size varies from 1 to 19 pups (average 8). The embryos lose their

external gills External gills are the gills of an animal, most typically an amphibian, that are exposed to the environment, rather than set inside the pharynx and covered by gill slits, as they are in most fishes. Instead, the respiratory organs are set on a fril ...

at a length of , have developed colouration by a length of , and are born at a length of . Males and females reach

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 definit ...

at approximately and long respectively.

Human interactions

Harmless to humans, the Australian weasel shark is commonly caught by

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' ...

and fish

ers operating off northern Australia. Smaller numbers are also captured in gillnets and on longlines. As this species has a relatively high reproductive rate and losses to fisheries are not severe enough to affect its population, it has been assessed as

by the

(IUCN).

References

{{Good article Australian weasel shark Marine fish of Northern Australia Australian weasel shark Australian weasel shark