Blacktip sawtail catshark
Encyclopedia
The blacktip sawtail catshark (Galeus sauteri) is a species
of catshark
, family
Scyliorhinidae, found off Taiwan
and the Philippines
. It is demersal in nature and occurs deeper than 60 m (196.9 ft). Growing up to 46 cm (18.1 in) long, this slim-bodied species is characterized by its plain brownish dorsal coloration with dark tips on the dorsal
and caudal fins, and a prominent crest of enlarged dermal denticles on the upper edge of the caudal fin. It is oviparous, with females producing encapsulated eggs two at a time year-round. The blacktip sawtail catshark is caught incidentally
in bottom trawls and used for fishmeal in Taiwan. However, the International Union for Conservation of Nature (IUCN) currently lacks enough information to assess its conservation status.
), Taiwan
by Hans Sauter. American ichthyologists David Starr Jordan
and Robert Earl Richardson described several new species from the collection in a 1909 issue of Memoirs of the Carnegie Museum, including a catshark of the genus Pristiurus that they named in Sauter's honor. Jordan and Richardson referenced six syntype
s 30–36 cm (11.8–14.2 in) long in their description, of which four survive to the present day. Later authors have recognized Pristiurus as a junior synonym of the genus Galeus
. A 2005 phylogenetic study, based on mitochondrial
and nuclear DNA
, found that this species, G. eastmani
, and G. gracilis
form a clade
apart from G. melastomus
and G. murinus
.
. It was once thought to occur off southern Japan
as well, but recent observations by Kazuhiro Nakaya have determined that this is not the case. This species is found on or near the bottom over the continental shelf
. In the Taiwan Strait
, it has been recorded over mud at depths of 60–90 cm (23.6–35.4 in), while off Guishan Island it is known from 100–200 m (328.1–656.2 ft).
s (protective third eyelids) and lack prominent ridges underneath. Behind each eye is a small spiracle
. The mouth is large and forms a long, wide arch; the corners of the mouth bear well-developed furrows. There are about 70–78 upper and 82 lower tooth rows. Each tooth is small and usually has five cusps, with the central one the longest. The five pairs of gill slit
s are short, with the fourth and fifth pairs located over the bases of the pectoral fins.
Both dorsal fin
s are rounded; the first is slightly larger and positioned over the latter half of the pelvic fin bases, while the second is positioned over the latter half of the anal fin base. The pectoral fins are medium-sized and blunt-cornered. The small pelvic fins are low and angular; the claspers of adult males reach the origin of the anal fin. The space between the pelvic and anal fin origins is greater in males than in females. The anal fin is elongated and angular; its base measures 12–15% of the total length, comparable to the distance between the dorsal fins. The caudal peduncle is compressed from side to side, and leads to a low caudal fin with a small lower fin and a ventral notch near the tip of the upper lobe. The body is covered by small, slightly overlapping dermal denticles, which are leaf-shaped with a median ridge and three marginal teeth. A crest of enlarged denticles is present along the upper edge of the caudal fin. This species is a uniform ochre above and white below, with distinctive dark brown tips on the dorsal and caudal fins; the interior of the mouth is light gray.
, on the right, and two functional oviduct
s; a single egg matures within each oviduct at a time. The eggs are enclosed in purse-shaped, translucent golden brown capsules measuring about 36–39 cm (14.2–15.4 in) long and 15 cm (5.9 in) across. The surface of the capsule is smooth and unlined; there are coiled tendrils on the anterior corners and bundles of long fibers on the posterior corners. Half of all males and females are sexually mature
at 35–36 cm (13.8–14.2 in) and 41–42 cm (16.1–16.5 in) long respectively. A known parasite of this species is the tapeworm Nakayacestus tanyderus.
in bottom trawls operated by commercial
shrimp
fisheries. Captured sharks are processed into fishmeal and used in aquaculture
. This species is probably also caught incidentally by bottom trawlers in the Philippines, as it has been observed at markets. Because specific catch data is lacking, the International Union for Conservation of Nature (IUCN) has listed the blacktip sawtail catshark 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, found off Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
and the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
. It is demersal in nature and occurs deeper than 60 m (196.9 ft). Growing up to 46 cm (18.1 in) long, this slim-bodied species is characterized by its plain brownish dorsal coloration with dark tips on the dorsal
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 caudal fins, and a prominent crest of enlarged dermal denticles on the upper edge of the caudal fin. It is oviparous, with females producing encapsulated eggs two at a time year-round. The blacktip sawtail catshark is caught incidentally
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 bottom trawls and used for fishmeal in Taiwan. However, the International Union for Conservation of Nature (IUCN) currently lacks enough information to assess its conservation status.
Taxonomy and phylogeny
In 1906, the Carnegie Museum purchased an extensive collection of fishes assembled from the markets of Takao (KaohsiungKaohsiung
Kaohsiung is a city located in southwestern Taiwan, facing the Taiwan Strait on the west. Kaohsiung, officially named Kaohsiung City, is divided into thirty-eight districts. The city is one of five special municipalities of the Republic of China...
), Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
by Hans Sauter. American ichthyologists David Starr Jordan
David Starr Jordan
David Starr Jordan, Ph.D., LL.D. was a leading eugenicist, ichthyologist, educator and peace activist. He was president of Indiana University and Stanford University.-Early life and education:...
and Robert Earl Richardson described several new species from the collection in a 1909 issue of Memoirs of the Carnegie Museum, including a catshark of the genus Pristiurus that they named in Sauter's honor. Jordan and Richardson referenced six syntype
Syntype
In biological nomenclature, a syntype is a term used to indicate a specimen with a special status.In zoological nomenclature, a syntype is defined as "Each specimen of a type series from which neither a holotype nor a lectotype has been designated [Arts. 72.1.2, 73.2, 74]. The syntypes...
s 30–36 cm (11.8–14.2 in) long in their description, of which four survive to the present day. Later authors have recognized Pristiurus as a junior synonym of the genus Galeus
Galeus
Galeus is a genus of catshark, family Scyliorhinidae, commonly known as sawtail catsharks in reference to a distinctive saw-toothed crest of enlarged dermal denticles found along the upper edges of their caudal fins. They are found in the Atlantic, the western and central Pacific, and the Gulf of...
. A 2005 phylogenetic study, 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...
, found that this species, 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...
, and G. gracilis
Slender sawtail catshark
The slender sawtail catshark is a little-known species of catshark, family Scyliorhinidae, endemic to northern Australia. It is found over the continental slope in on water...
form 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
The blacktip sawtail catshark is found in the waters around Taiwan, where it is very common, and the PhilippinesPhilippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
. It was once thought to occur off southern Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
as well, but recent observations by Kazuhiro Nakaya have determined that this is not the case. This species is found on or near the bottom over the continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
. In the Taiwan Strait
Taiwan Strait
The Taiwan Strait or Formosa Strait, formerly known as the Black Ditch, is a 180-km-wide strait separating Mainland China and Taiwan. The strait is part of the South China Sea and connects to East China Sea to the northeast...
, it has been recorded over mud at depths of 60–90 cm (23.6–35.4 in), while off Guishan Island it is known from 100–200 m (328.1–656.2 ft).
Description
A small species, the blacktip sawtail catshark attains a maximum length of 46 cm (18.1 in). Its body is slim and firm, with the head comprising roughly one-fifth of the total length. The rather long snout is pointed, with large nostrils divided by triangular flaps of skin on their anterior margins. The large, horizontally oval eyes bear 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) and lack prominent ridges underneath. Behind each eye is a small 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 mouth is large and forms a long, wide arch; the corners of the mouth bear well-developed furrows. There are about 70–78 upper and 82 lower tooth rows. Each tooth is small and usually has five cusps, with the central one the longest. The 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 are short, with the fourth and fifth pairs located over the bases of the pectoral fins.
Both 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 are rounded; the first is slightly larger and positioned over the latter half of the pelvic fin bases, while the second is positioned over the latter half of the anal fin base. The pectoral fins are medium-sized and blunt-cornered. The small pelvic fins are low and angular; the claspers of adult males reach the origin of the anal fin. The space between the pelvic and anal fin origins is greater in males than in females. The anal fin is elongated and angular; its base measures 12–15% of the total length, comparable to the distance between the dorsal fins. The caudal peduncle is compressed from side to side, and leads to a low caudal fin with a small lower fin and a ventral notch near the tip of the upper lobe. The body is covered by small, slightly overlapping dermal denticles, which are leaf-shaped with a median ridge and three marginal teeth. A crest of enlarged denticles is present along the upper edge of the caudal fin. This species is a uniform ochre above and white below, with distinctive dark brown tips on the dorsal and caudal fins; the interior of the mouth is light gray.
Biology and ecology
Reproduction in the blacktip sawtail catshark is oviparous and proceeds throughout the year, without well-defined seasonal patterns. Adult females have a single functional ovaryOvary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
, on the right, and two functional oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...
s; a single egg matures within each oviduct at a time. The eggs are enclosed in purse-shaped, translucent golden brown capsules measuring about 36–39 cm (14.2–15.4 in) long and 15 cm (5.9 in) across. The surface of the capsule is smooth and unlined; there are coiled tendrils on the anterior corners and bundles of long fibers on the posterior corners. Half of all males and females are sexually 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...
at 35–36 cm (13.8–14.2 in) and 41–42 cm (16.1–16.5 in) long respectively. A known parasite of this species is the tapeworm Nakayacestus tanyderus.
Human interactions
In Taiwanese waters, blacktip sawtail catsharks of most sizes are frequently 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...
in bottom trawls operated by 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...
shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
fisheries. Captured sharks are processed into fishmeal and used in aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
. This species is probably also caught incidentally by bottom trawlers in the Philippines, as it has been observed at markets. Because specific catch data is lacking, the International Union for Conservation of Nature (IUCN) has listed the blacktip sawtail catshark 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...
.