Squatina japonica, Bleeker 1858 : 40, valid, holotype (unique): RMNH 7416 (Eschmeyer, 2005). Figure 4.
Common name. Japanese angel shark.
Diagnosis. A list of the following distinctive characters: wide but shallow upper lip arch (4.2-5.0% TL in width, 0.8-1.1% TL in height); spiracles with numerous large papillae on inside anterior edge, papillae boxlike in shape; row of thorny tubercles on dorsal originating mid-back and extending to the caudal peduncle; pelvic fins not reaching origin of first dorsal; dorsal fins angular in shape, dorsal bases roughly equal; rusty brown coloration above with fine spotting pattern of numerous small square-shaped spots throughout.
Description. Dorsal surface, except for posterior portion of caudal fin, covered with denticles of moderate roughness. Row of tubercles extending posterior from mid-back, also present interdorsal and dorsal-caudal space but smaller in size. Ventral surface smooth except for narrow bands of denticles on the pectoral and pelvic fins.
Head somewhat diamond in shape dorsally, length about 0.2 times total length, greatest width occurring just anterior of first gill opening. Interspersed moderately rough tubercles above mouth and eye crests. Eyes almond-shaped, widely set, interorbital space (9.1; 8.8-9.5). Eye-spiracle space short. Interspiracle space (10.0; 9.7-10.3) slightly greater than interorbital space. Spiracles crescent shaped with large box-like papillae on inside anterior margin. Center of upper lip exposed forming a broad narrow arch, extends nearly one half the height of upper lip space, upper lip arch height (0.9; 0.8-1.1), upper lip arch width (4.7; 4.2-5.0). Labial furrows conspicuous, extending from corners of mouth medially. Upper furrows partially concealed with dermal skin lobes. Upper labial furrows about 1.2 times longer than lower labial furrows. Small nasal flaps protruding from dermal folds above mouth with two barbels protruding from each flap. Inner nasal barbel spatulate with inner basal portion containing little if any fringe. Outer nasal barbel narrow. Nostrils large and slightly protruding. Slight lobes present at corners of mouth extending ventrally. Mouth length about 0.2 times as long as mouth width. Dentition consisting of small, dagger-like teeth, conical without cusplets on a broad base, in 3 orderly longitudinal rows, no teeth at symphysis, teeth by row 10 - 10 / 10 - 10.
Pectoral fins large, somewhat rounded posteriorly, originating just behind gills. Anterior margin of pectoral fin, slightly curvilinear, about equal to pectoral fin length, extending to lateral apex. Angle of lateral apex slightly more obtuse than 90°. Margin from lateral apex to most posterior lobe straight to slightly concave. Posterior lobe moderately convex. Pectoral inner margin broadly convex.
Pelvic fins, originating anterior to pectoral posterior free tip, somewhat triangular with rounded fintips. Anterior margin, slightly convex, approximately 0.6 times as long as pelvic fin length, extends at roughly a 45° angle from trunk to broadly rounded lateral apex. Pelvic girdle width (33.1; 32.1-34.5) very broad. Posterior margin of pelvic fin straight to posterior free tips which do not reach origin of first dorsal. Pelvic inner margin straight to insertion of pelvic fin.
Dorsal fins lobe-like and about identical in size, with denticles extending over the whole of the fins. Interdorsal space about 0.9 times as long as dorsal caudal finspace. Anterior margins of dorsals convex, nearly equidistant. Dorsal bases nearly equal, first dorsal base (3.0; 2.8-3.2), second dorsal base (3.0; 2.7-3.2). Apex of dorsals lobed. Posterior margins slightly convex, about 0.6 times as long as anterior margins. Inner margins of dorsals slightly convex, approximately 0.4 times as long as anterior margins.
Caudal peduncle compressed dorso-ventrally with large lateral longitudinal ridges, tapering posteriorly.
Caudal fin angular throughout, especially dorsally. Caudal dorsal margin about 0.8 times as long as caudal preventral margin. Dorsal lobe somewhat triangular with rounded apex. Subterminal caudal fin margin present in all but one specimen, approximately 0.4 times as long as upper postventral caudal margin. Lower caudal postventral margin straight to slightly convex, about 0.9 times as long as upper caudal postventral margin.
Coloration. Dorsal surface of specimens prior to preservation light to dark brown throughout with a distinct freckled pattern of numerous square-shaped black spots. Spots slightly smaller on edges of trunk and fins, absent on dorsals above base and caudal outside of caudal vertebral column. Larger black splotches laterally at origins of dorsals. Ventral surface pale white with some black mottling, pectoral and pelvic fin ventral margins with denticles colored similar to dorsal. After preservation color tends to fade to a lighter brown, spotting pattern can also fade to blend in with overall color.
Distribution. Endemic to the WNP including the Sea of Japan, along the south eastern Japan coast, Yellow Sea, East China Sea, waters surrounding northern Taiwan, and the Taiwan Strait (Shuyuan, 1994; Randall & Lim, 2000; Compagno et al., 2005a).
Etymology. Naming is in allusion to where the holotype was described (Japan).
Remarks. Squatina japonica is the only WNP species in this study to possess mid-back thorns. Compagno, 1984 illustrates S. nebulosa as possessing midback thorns, but we did not observe these in any of the specimens we examined. Midback thorns are also not present on the holotypes of S. formosa or S. nebulosa , and photographs and illustrations of S. tergocellatoides specimens.
Literature descriptions (Lindberg & Legeza, 1967) indicate that interspiracle distance is greater than interorbital distance in S. japonica ; a finding consistent with our observations.
Material Examined. HUMZ 107395, immature female, off Shirahama, Shimoda City, Shizuoka prefecture , Japan , 27 Jan 1986 , caught with a bottom gill net at 30 m ; HUMZ 105913 immature male, off Itado, Shimoda, Shizuoka prefecture , Japan , 19 Nov 1985 , caught with a bottom gill net at 10m ; CAS 20955: immature male, Japan , Tokyo Market, collected by R/V Snyder and Sindo as part of the “Albatross 1906 cruise ; ” CAS 20956, immature male, Japan , Tokyo market, collected by R/V Snyder and Sindo as part of the “Albatross 1906 cruise.”
The Japanese angelshark (Squatina japonica) is a species of angelshark, family Squatinidae, found in the northwestern Pacific Ocean off China, Japan, and Korea. It is a bottom-dwelling shark found in sandy habitats down to 300 m (980 ft) deep. This species has the flattened shape with wing-like pectoral and pelvic fins typical of its family, and grows to 1.5 m (4.9 ft) or more in length. Its two dorsal fins are placed behind the pelvic fins, and a row of large thorns occurs along its dorsal midline. Its upper surface is cryptically patterned, with numerous squarish dark spots on a brown background.
Feeding on fishes, cephalopods, and crustaceans, the Japanese angelshark is a nocturnal ambush predator that spends most of the day lying still on the sea floor. This species gives birth to live young, which are sustained during gestation by yolk. The litter size varies from two to 10. The Japanese angelshark is not dangerous to humans unless provoked. It is fished in large numbers and used for meat and shagreen, a type of leather.
The Japanese angelshark was described by Dutch ichthyologist Pieter Bleeker in an 1858 volume of the scientific journal Acta Societatis Scientiarum Indo-Neerlandicae. The type specimen is a male 53 cm (21 in) long, collected off Nagasaki, Japan, hence the specific epithet japonica.[2][3] Other common names for this species include change angel shark, change canopy shark, Japanese angelfish, and Japanese monkfish.[4]
Using mitochondrial DNA, a 2010 phylogenetic analysis reported that the Japanese angelshark forms a clade with the other Asian angelsharks included in the study: the ocellated angelshark (S. tergocellatoides) and the sister species pair of the Taiwan angelshark (S. formosa) and the Indonesian angelshark (S. legnota). These Asian species are, in turn, allied with European and North African angel shark species. Molecular clock estimation suggested the Japanese angelshark lineage diverged from the rest of the Asian angelsharks some 100 million years ago during the Cretaceous.[5]
The Japanese angelshark is fairly narrow-bodied and has greatly enlarged pectoral and pelvic fins. The skin folds along the sides of the head lack distinct lobes. The eyes are oval and widely spaced; closely behind are crescent-shaped spiracles with large, boxy projections inside their anterior rims. Each nostril is large and preceded by a small flap of skin bearing two barbels; the outer barbel is thin, while the inner barbel has a spoon-like tip and a smooth to slightly fringed flange at the base. The wide mouth is terminally placed and has furrows at the corners. There are 10 tooth rows on either side of both jaws, separated by a gap in the middle; the teeth are small, narrow, and pointed. There are five pairs of gill slits located on the sides of the head.[3][6]
The frontmost portion of each pectoral fin forms a triangular lobe separate from the head. The outer corners of the pectoral fins are angular, and their rear tips are rounded. The pelvic fins have convex margins. The two angular dorsal fins are similar in shape and size, and are located behind the pelvic fins. The caudal peduncle is flattened with a keel running along either side, and supports a roughly triangular caudal fin with rounded corners. The lower lobe of the caudal fin is larger than the upper. The dorsal surface is covered by medium-sized dermal denticles, and a distinctive row of large thorns is present along the midline of the back and tail. This species is light to dark brown above with a dense covering of squarish dark spots, which become finer on the fins. The underside is white with darker mottling.[3][6] Various sources give differing maximum lengths, ranging from 1.5 to 2.5 m (4.9 to 8.2 ft).[1][7]
The Japanese angelshark is native to the cooler waters of the northwestern Pacific; its range extends from the eastern coast of Honshu, Japan, to Taiwan, and includes the southern Sea of Japan, the Yellow Sea, the East China Sea, and the Taiwan Strait.[6] Some older sources reported it may occur in the Philippines, but recent research suggests the only angel shark species in that area is S. caillieti.[3][8] The Japanese angelshark inhabits the continental shelf, usually in the shallows, but also to as deep as 300 m (980 ft). It is a bottom-dweller found over sandy bottoms, often close to rocky reefs.[1][7]
During the day, the Japanese angelshark mostly lies partly buried on the bottom; its complex color pattern provides camouflage as it ambushes nearby prey. At night, this species becomes more active. Its diet consists of demersal fishes, cephalopods, and crustaceans. It may be found alone or in proximity to others of its species.[9] Parasites documented from this species include the tapeworms Phyliobothrium marginatum and Tylocephalum squatinae,[10] the copepods Eudactylina squatini[11] and Trebius shiinoi,[12] and the praniza larvae of the isopod Gnathia trimaculata.[13] The Japanese angelshark is viviparous, and as in other members of its family the developing embryos are nourished by yolk. Litters of two to ten pups are birthed in spring and summer, with the newborns measuring 22 cm (8.7 in) long. Females mature sexually at 80 cm (31 in) long, while male maturation size is unknown.[1]
The Japanese angelshark is typically inoffensive towards humans, but if disturbed, can inflict a severe bite. Across much of its range, it is a frequent catch (intentional or not) in bottom trawls and probably also set nets and demersal gillnets; the meat is eaten and the rough skin is made into a type of leather called shagreen for use in wood finishing.[1][3]
Angel sharks in general are highly threatened by commercial trawl fisheries due to their susceptibility to capture and low rate of reproduction, and angel shark species elsewhere are known to have declined markedly under fishing pressure. Trawling activity in the Yellow Sea and other parts of the northwestern Pacific is intense and, coupled with pollution, has had a serious impact on the local ecosystem. The Japanese angelshark population is suspected to have declined by up to 50% or more under these conditions, leading the species to be assessed as critically endangered by the International Union for Conservation of Nature (IUCN). It may benefit from a ban on trawling imposed in some areas by the Chinese government, though enforcement is inconsistent.[1]
The Japanese angelshark (Squatina japonica) is a species of angelshark, family Squatinidae, found in the northwestern Pacific Ocean off China, Japan, and Korea. It is a bottom-dwelling shark found in sandy habitats down to 300 m (980 ft) deep. This species has the flattened shape with wing-like pectoral and pelvic fins typical of its family, and grows to 1.5 m (4.9 ft) or more in length. Its two dorsal fins are placed behind the pelvic fins, and a row of large thorns occurs along its dorsal midline. Its upper surface is cryptically patterned, with numerous squarish dark spots on a brown background.
Feeding on fishes, cephalopods, and crustaceans, the Japanese angelshark is a nocturnal ambush predator that spends most of the day lying still on the sea floor. This species gives birth to live young, which are sustained during gestation by yolk. The litter size varies from two to 10. The Japanese angelshark is not dangerous to humans unless provoked. It is fished in large numbers and used for meat and shagreen, a type of leather.
