Slender sawtail catshark
Encyclopedia
The slender sawtail catshark (Galeus gracilis) is a little-known species
of catshark
, family
Scyliorhinidae, endemic to northern Australia. It is found over the continental slope in 290–470 m (951.4–1,542 ft) on water. Growing to 34 cm (13.4 in) long, this shark has a slim gray body with four dark saddle markings below the dorsal fin
s and on the caudal fin, as well as a prominent crest of enlarged dermal denticles along the dorsal edge of the caudal fin. The slender sawtail catshark is not valued by fisheries but is taken as bycatch
. The International Union for Conservation of Nature (IUCN) presently lacks enough information to assess its conservation status.
and John Stevens described the slender sawtail catshark in a 1993 issue of the scientific journal
Records of the Australian Museum. They gave it the specific epithet gracilis, meaning "slender" in Latin
; previously, the species had been provisionally termed Galeus sp. A. The type specimen is a 34 cm (13.4 in) long adult female, caught in January 1988 north of Melville Island, Northern Territory
. Within the genus, G. gracilis appears to be closely related to G. eastmani
, G. longirostris, and G. nipponensis
. A 2005 phylogenetic analysis, based on mitochondrial
and nuclear DNA
, reported that this species, G. eastmani, and G. sauteri
formed a clade
apart from G. melastomus
and G. murinus
.
, off Melville Island off Northern Territory, and off Cape York
in Queensland
. It may also be present in eastern Indonesia
n waters. It is unknown whether these scattered records represent separate populations or a single continuous population. Demersal in nature, this shark inhabits the continental slope at a depth of 290–470 m (951.4–1,542 ft).
s (protective third eyelids). Below each eye is a thin ridge, and behind is a tiny spiracle
. The nostrils are divided by small, triangular flaps of skin in front. The mouth forms a wide arch and bears moderately long furrows around the corners. The teeth are small and closely set, numbering 54–57 rows in the upper jaw and 54–62 rows in the lower jaw. Each tooth has a narrow central cusp usually flanked by one, occasionally two small cusplets on either side. The teeth of males are slightly larger and longer than those of females. There are five pairs of gill slit
s, with the fourth and fifth pairs over the pectoral fin bases.
The first dorsal fin
slightly exceeds the second in size and originates over the midpoint of the pelvic fin bases. The second dorsal fin is positioned over the last third of the anal fin. The dorsal fins have rounded apexes. The short, wide pectoral fins are roughly triangular, with rounded corners. The pelvic and anal fins are long-based, low, and fairly angular. Adult males have long, tapering claspers, each with saw-like rows of denticles along the inner surface, and twisted tips. The anal fin base measures around 11% of the total length and exceeds or matches the distances between the anal fin and the pelvic and caudal fins. The caudal fin is narrow, with a small but distinct lower lobe and a ventral notch near the tip of the upper lobe. The body and fins are densely covered by tiny, overlapping dermal denticles. Each has a teardrop-shaped crown covered by small pits, and bears a central ridge and typically three marginal teeth. There is a crest of enlarged denticles along the front portion of the caudal fin dorsal margin. This species is light gray above and lighter below; there is a small, dark saddle below each dorsal fin base, as well as two more saddles on the caudal fin, the second of which almost forms a complete ring. Some sharks also have a faint darker blotch over each flank. The inner lining of the mouth is dark gray.
at a length of 33 cm (13 in).
by the Western Trawl Fishery operating off northwestern Australia. There is no direct fishing for this species as it has no commercial value. Given a lack of information on conservation threats, the International Union for Conservation of Nature (IUCN) has listed this species as Data Deficient
.
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 catshark
Catshark
Catsharks are ground sharks of the family Scyliorhinidae, with over 150 known species. While they are generally known as catsharks, many species are commonly called dogfish....
, 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...
Scyliorhinidae, endemic to northern Australia. It is found over the continental slope in 290–470 m (951.4–1,542 ft) on water. Growing to 34 cm (13.4 in) long, this shark has a slim gray body with four dark saddle markings below the 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...
s and on the caudal fin, as well as a prominent crest of enlarged dermal denticles along the dorsal edge of the caudal fin. The slender sawtail catshark is not valued by fisheries but is taken as bycatch
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...
. The International Union for Conservation of Nature (IUCN) presently lacks enough information to assess its conservation status.
Taxonomy and phylogeny
Leonard CompagnoLeonard 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,...
and John Stevens described the slender sawtail catshark in a 1993 issue of the scientific journal
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
Records of the Australian Museum. They gave it the specific epithet gracilis, meaning "slender" in Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
; previously, the species had been provisionally termed Galeus sp. A. The type specimen is a 34 cm (13.4 in) long adult female, caught in January 1988 north of Melville Island, Northern Territory
Melville Island, Northern Territory
Melville Island or Yermalner Island lies in the eastern Timor Sea, off the coast of the Northern Territory of Australia. It is west of the Cobourg Peninsula in Arnhem Land and north of Darwin....
. Within the genus, G. gracilis appears to be closely related to G. eastmani
Gecko catshark
The gecko catshark is a species of catshark, family Scyliorhinidae, native to the northwestern Pacific Ocean from southern Japan to Taiwan, and possibly also off Vietnam. It is a common, demersal species found at depths of . Its body is slender, with a pattern of dark saddles and blotches...
, G. longirostris, and G. nipponensis
Broadfin sawtail catshark
The broadfin sawtail catshark is a common species of catshark, family Scyliorhinidae. It is found on or near the bottom at depths of , from southeastern Japan to the East China Sea...
. A 2005 phylogenetic analysis, based on mitochondrial
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
and nuclear DNA
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...
, reported that this species, G. eastmani, and G. sauteri
Blacktip sawtail catshark
The blacktip sawtail catshark is a species of catshark, family Scyliorhinidae, found off Taiwan and the Philippines. It is demersal in nature and occurs deeper than...
formed a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
apart from G. melastomus
Blackmouth catshark
The blackmouth catshark is a species of catshark, family Scyliorhinidae, common in the northeastern Atlantic Ocean from Iceland to Senegal, including the Mediterranean Sea. It is typically found over the continental slope at depths of , on or near muddy bottoms. The youngest sharks generally...
and G. murinus
Mouse catshark
The mouse catshark is a species of catshark, family Scyliorhinidae, common in the northeastern Atlantic Ocean, from Iceland to Western Sahara. There is much taxonomic confusion regarding this species in Icelandic waters, where it may be confounded with another species of Galeus or Apristurus...
.
Distribution and habitat
Apparently rare, the slender sawtail catshark has been collected from off Cape Cuvier and Port Hedland in Western AustraliaWestern 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...
, off Melville Island off Northern Territory, and off Cape York
Cape York
Cape York may refer to:* Cape York , a cape at the north-west coast of Greenland, in northern Baffin Bay* Cape York meteorite, meteorite found in 1894 near Cape York, Greenland...
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 may also be present in eastern Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
n waters. It is unknown whether these scattered records represent separate populations or a single continuous population. Demersal in nature, this shark inhabits the continental slope at a depth of 290–470 m (951.4–1,542 ft).
Description
A small species growing to at least 34 cm (13.4 in) long, the slender sawtail catshark has a slim body with a nearly cylindrical cross-section, and a short, narrow head with a rounded snout. The eyes are horizontally oval and equipped with rudimentary 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). Below each eye is a thin ridge, and behind is a tiny spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
. The nostrils are divided by small, triangular flaps of skin in front. The mouth forms a wide arch and bears moderately long furrows around the corners. The teeth are small and closely set, numbering 54–57 rows in the upper jaw and 54–62 rows in the lower jaw. Each tooth has a narrow central cusp usually flanked by one, occasionally two small cusplets on either side. The teeth of males are slightly larger and longer than those of females. 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 fourth and fifth pairs over the pectoral fin bases.
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...
slightly exceeds the second in size and originates over the midpoint of the pelvic fin bases. The second dorsal fin is positioned over the last third of the anal fin. The dorsal fins have rounded apexes. The short, wide pectoral fins are roughly triangular, with rounded corners. The pelvic and anal fins are long-based, low, and fairly angular. Adult males have long, tapering claspers, each with saw-like rows of denticles along the inner surface, and twisted tips. The anal fin base measures around 11% of the total length and exceeds or matches the distances between the anal fin and the pelvic and caudal fins. The caudal fin is narrow, with a small but distinct lower lobe and a ventral notch near the tip of the upper lobe. The body and fins are densely covered by tiny, overlapping dermal denticles. Each has a teardrop-shaped crown covered by small pits, and bears a central ridge and typically three marginal teeth. There is a crest of enlarged denticles along the front portion of the caudal fin dorsal margin. This species is light gray above and lighter below; there is a small, dark saddle below each dorsal fin base, as well as two more saddles on the caudal fin, the second of which almost forms a complete ring. Some sharks also have a faint darker blotch over each flank. The inner lining of the mouth is dark gray.
Biology and ecology
Virtually nothing is known of the slender sawtail catshark's natural history. Males mature sexuallySexual 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...
at a length of 33 cm (13 in).
Human interactions
Unknown numbers of slender sawtail catsharks are 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 the Western Trawl Fishery operating off northwestern Australia. There is no direct fishing for this species as it has no commercial value. Given a lack of information on conservation threats, the International Union for Conservation of Nature (IUCN) has listed this species as Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
.