Broadfin sawtail catshark
Encyclopedia
The broadfin sawtail catshark (Galeus nipponensis) is a common species
of catshark
, family
Scyliorhinidae. It is found on or near the bottom at depths of 150–540 m (492.1–1,771.7 ft), from southeastern Japan
to the East China Sea
. A slender species growing to 68 cm (26.8 in) long, this shark is characterized by a fairly long, pointed snout, a series of indistinct, dark saddles along its back and tail, and a prominent crest of enlarged dermal denticles along the dorsal edge of its caudal fin. In addition, adult males have very long claspers that reach past the anal fin. The broadfin sawtail catshark is an opportunistic predator of bony fishes, cephalopod
s, and crustacean
s, with immature and mature sharks being primarily piscivorous. It is oviparous and reproduces year-round. The International Union for Conservation of Nature (IUCN) presently lacks the information to assess the conservation status of this species.
(G. eastmani), under whose name authors such as Toshiji Kamohara had described it since 1950. This shark was formally described as a new species in a 1975 volume of the scientific journal
Memoirs of the Faculty of Fisheries, Hokkaido University by Kazuhiro Nakaya, who gave it the specific epithet nipponensis from Nippon
(Japan
). The type specimen is a 60 cm (23.6 in) long adult male caught off Mimase in Kochi Prefecture
, on December 20, 1972. Within the genus, this species is closest in morphology
to the longnose sawtail catshark (G. longirostris).
off southeastern Honshu
, Japan to the East China Sea
, including the Ryukyu Islands
and the Kyushu-Palau Ridge
. It is reportedly common in Japanese waters. This demersal species has been recorded from water between 150 and 540 m (492.1 and 1,771.7 ft) deep.
s (protective third eyelids). Beneath each eye is a subtle ridge, and behind is a small spiracle
. The capacious mouth forms a long, wide arch; well-developed furrows are present at the corners. The small teeth each have a narrow central cusp flanked by usually one, sometimes more, smaller cusplets on both sides. The five pairs of gill slit
s are short, with the last pair over the pectoral fin bases.
The first dorsal fin
is roughly triangular, with gently convex anterior and posterior margins, and originates over the midpoint of the pelvic fin bases. The second dorsal fin is slightly smaller than the first and similar in shape, and originates over the latter portion of the anal fin base. The pectoral fins are medium-sized and broad. The pelvic fins are sizable and relatively low, with angular corners. In adult males, the inner margins of the pelvic fins are partially fused to form an "apron" over the bases of the claspers, which are very long and thin, reaching past the origin of the small anal fin. The base of the anal fin measures 8–10% of the total length, much less than the distances between either the pelvic and anal fins or the two dorsal fins. The anal fin of the male is 2% shorter than that of the female, which may be related to the function of the unusually long claspers. The caudal peduncle is almost cylindrical, and leads to a low caudal fin with a small lower lobe and a ventral notch near the tip of the upper lobe. The dermal denticles are small and overlapping, each with a leaf-shaped crown bearing a median ridge and three marginal teeth. There is a saw-toothed crest of enlarged denticles along the upper edge of the caudal fin. This species is dark gray above, with a series of faint darker saddles along the body and tail. The underside, inside of the mouth, and trailing margins of the pectoral and dorsal fins are white.
es), cephalopod
s (including sepiolid
and enoploteuthid
squid
), and crustacean
s (including isopods, krill
, and decapod
s). Young sharks exhibit greater variation in diet across seasons than immature and mature sharks, which consistently feed predominantly on fish. The dietary composition of young sharks in Suruga Bay
differs from that of the co-occurring gecko catshark
(G. eastmani), perhaps to reduce interspecific competition
.
Reproduction in the broadfin sawtail catshark is oviparous; adult females have a single functional ovary
, on the right, and two functional oviduct
s. Only a single egg may mature within each oviduct at a time. The egg case is vase-shaped and measures roughly 9 cm (3.5 in) long and 2 cm (0.78740157480315 in) across, with thick, opaque, brown walls bearing fine, lengthwise grooves; the top of the case is squared off, while the bottom is rounded with a short membraneous projection. Females lay eggs throughout the year, with a peak in December and January. The young shark hatches at about 13 cm (5.1 in) long. Males mature sexually
at 51–62 cm (20.1–24.4 in) long, and females at 55–61 cm (21.7–24 in) long.
. It is caught incidentally
to an unknown degree in bottom trawls operated by commercial deepwater fisheries
off Japan and in the East China Sea.
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. It is found on or near the bottom at depths of 150–540 m (492.1–1,771.7 ft), from southeastern 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...
to the East China Sea
East China Sea
The East China Sea is a marginal sea east of China. It is a part of the Pacific Ocean and covers an area of 1,249,000 km² or 750,000 square miles.-Geography:...
. A slender species growing to 68 cm (26.8 in) long, this shark is characterized by a fairly long, pointed snout, a series of indistinct, dark saddles along its back and tail, and a prominent crest of enlarged dermal denticles along the dorsal edge of its caudal fin. In addition, adult males have very long claspers that reach past the anal fin. The broadfin sawtail catshark is an opportunistic predator of bony fishes, cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, 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, with immature and mature sharks being primarily piscivorous. It is oviparous and reproduces year-round. The International Union for Conservation of Nature (IUCN) presently lacks the information to assess the conservation status of this species.
Taxonomy
The broadfin sawtail catshark has long been lumped together with the closely similar but smaller gecko catsharkGecko 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. eastmani), under whose name authors such as Toshiji Kamohara had described it since 1950. This shark was formally described as a new species in a 1975 volume 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...
Memoirs of the Faculty of Fisheries, Hokkaido University by Kazuhiro Nakaya, who gave it the specific epithet nipponensis from Nippon
Nippon
Nippon is a native name for Japan, more formal than Nihon.Nippon can also refer to:-Company names:All of the following companies are based in Japan.*Nikon *Nippon Telegraph and Telephone...
(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...
). The type specimen is a 60 cm (23.6 in) long adult male caught off Mimase in Kochi Prefecture
Kochi Prefecture
is a prefecture of Japan located on the south coast of Shikoku. The capital is the city of Kōchi.- History :Prior to the Meiji Restoration, Kōchi was known as Tosa Province and was controlled by the Chosokabe clan in the Sengoku period and the Yamauchi family during the Edo period.- Geography...
, on December 20, 1972. Within the genus, this species is closest in morphology
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....
to the longnose sawtail catshark (G. longirostris).
Distribution and habitat
The broadfin sawtail catshark is found in the northwestern Pacific from Sagami BaySagami Bay
Sagami Bay , also known as the Sagami Gulf or Sagami Sea, lies south of Kanagawa Prefecture in Honshū, central Japan, contained within the scope of the Miura Peninsula, in Kanagawa, to the east, the Izu Peninsula, in Shizuoka Prefecture, to the west, and the Shōnan coastline to the north, while the...
off southeastern Honshu
Honshu
is the largest island of Japan. The nation's main island, it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait...
, Japan to the East China Sea
East China Sea
The East China Sea is a marginal sea east of China. It is a part of the Pacific Ocean and covers an area of 1,249,000 km² or 750,000 square miles.-Geography:...
, including the Ryukyu Islands
Ryukyu Islands
The , also known as the , is a chain of islands in the western Pacific, on the eastern limit of the East China Sea and to the southwest of the island of Kyushu in Japan. From about 1829 until the mid 20th century, they were alternately called Luchu, Loochoo, or Lewchew, akin to the Mandarin...
and the Kyushu-Palau Ridge
Izu-Bonin-Mariana Arc
The Izu-Bonin-Mariana arc system is an outstanding example of a plate tectonic convergent boundary. IBM extends over 2800 km south from Tokyo, Japan, to beyond Guam, and includes the Izu Islands, Bonin Islands, and Mariana Islands; much more of the IBM arc system is submerged below sealevel...
. It is reportedly common in Japanese waters. This demersal species has been recorded from water between 150 and 540 m (492.1 and 1,771.7 ft) deep.
Description
Attaining a maximum known length of 68 cm (26.8 in), the broadfin sawtail catshark has a slim, firm body and a head comprises less than one-fifth of the total length. The snout is rather long, flattened, and pointed, with large nostrils that bear triangular skin flaps on their anterior rims. The sizable 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). Beneath each eye is a subtle ridge, and behind 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 capacious mouth forms a long, wide arch; well-developed furrows are present at the corners. The small teeth each have a narrow central cusp flanked by usually one, sometimes more, smaller cusplets on both sides. 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 last pair 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...
is roughly triangular, with gently convex anterior and posterior margins, and originates over the midpoint of the pelvic fin bases. The second dorsal fin is slightly smaller than the first and similar in shape, and originates over the latter portion of the anal fin base. The pectoral fins are medium-sized and broad. The pelvic fins are sizable and relatively low, with angular corners. In adult males, the inner margins of the pelvic fins are partially fused to form an "apron" over the bases of the claspers, which are very long and thin, reaching past the origin of the small anal fin. The base of the anal fin measures 8–10% of the total length, much less than the distances between either the pelvic and anal fins or the two dorsal fins. The anal fin of the male is 2% shorter than that of the female, which may be related to the function of the unusually long claspers. The caudal peduncle is almost cylindrical, and leads to a low caudal fin with a small lower lobe and a ventral notch near the tip of the upper lobe. The dermal denticles are small and overlapping, each with a leaf-shaped crown bearing a median ridge and three marginal teeth. There is a saw-toothed crest of enlarged denticles along the upper edge of the caudal fin. This species is dark gray above, with a series of faint darker saddles along the body and tail. The underside, inside of the mouth, and trailing margins of the pectoral and dorsal fins are white.
Biology and ecology
The broadfin sawtail catshark is an opportunistic predator known to consume a wide variety of bony fishes (including Sardinops melanostictus, Glossandon semifasciatus, Chlorophthalmus albatrossis and lanternfishLanternfish
Cooper Lanternfishes are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented by 246 species in 33 genera, and are found in oceans worldwide. They are aptly named after their conspicuous use of bioluminescence...
es), cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s (including sepiolid
Sepiolidae
Sepiolidae is a family of bobtail squid encompassing 15 genera in three or four subfamilies....
and enoploteuthid
Enoploteuthidae
Enoploteuthidea is a family of squid comprising approximately 40 species in 4 genera. Most species have a mantle length ranging from 3-13 cm. Hooks are present on all arms and tentacles...
squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
), 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 (including isopods, krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
, and decapod
Decapoda
The decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. It is estimated that the order contains nearly 15,000 species in around 2,700 genera, with...
s). Young sharks exhibit greater variation in diet across seasons than immature and mature sharks, which consistently feed predominantly on fish. The dietary composition of young sharks in Suruga Bay
Suruga Bay
Suruga Bay is a bay on the Pacific coast of Honshū in Shizuoka Prefecture, Japan. It is situated north of an imaginary line joining Omaezaki Point and Irōzaki Point at the tip of the Izu Peninsula and surrounded by Honshū to the southwest and west and the Izu Peninsula to the east.-Geology:Suruga...
differs from that of the co-occurring gecko catshark
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. eastmani), perhaps to reduce interspecific competition
Interspecific competition
Interspecific competition, in ecology, is a form of competition in which individuals of different species compete for the same resource in an ecosystem...
.
Reproduction in the broadfin sawtail catshark is oviparous; adult females have a single functional ovary
Ovary
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. Only a single egg may mature within each oviduct at a time. The egg case is vase-shaped and measures roughly 9 cm (3.5 in) long and 2 cm (0.78740157480315 in) across, with thick, opaque, brown walls bearing fine, lengthwise grooves; the top of the case is squared off, while the bottom is rounded with a short membraneous projection. Females lay eggs throughout the year, with a peak in December and January. The young shark hatches at about 13 cm (5.1 in) long. Males mature sexually
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 51–62 cm (20.1–24.4 in) long, and females at 55–61 cm (21.7–24 in) long.
Human interactions
The International Union for Conservation of Nature (IUCN) does not have enough specific data on the broadfin sawtail catshark to assess it beyond Data DeficientData 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...
. It 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...
to an unknown degree in bottom trawls operated by commercial deepwater 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...
off Japan and in the East China Sea.