| Blotchy swellshark | |
|---|---|
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Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Division: | Selachii |
| Order: | Carcharhiniformes |
| Family: | Scyliorhinidae |
| Genus: | Cephaloscyllium |
| Species: | C. umbratile |
| Binomial name | |
| Cephaloscyllium umbratile D. S. Jordan &Fowler, 1903 | |
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| Range of the blotchy swell shark[2] | |
Theblotchy swellshark orJapanese swellshark (Cephaloscyllium umbratile) is a commonspecies ofcatshark, belonging to thefamilyScyliorhinidae. The Blotchy swellshark is found at depths of 90–200 m (300–660 ft) in the northwesternPacific Ocean, fromJapan toTaiwan. It isbenthic in nature and favors rockyreefs. Reaching 1.4 m (4.6 ft) in length, this thick-bodied shark has a broad head, large mouth, and two unequally-sizeddorsal fins positioned far back past thepelvic fins. It can be identified by its dorsal coloration, consisting of seven brown "saddles" and extensive darker mottling on a light tan background. This species has often been confounded with thedraughtsboard shark (C. isabellum) and theSarawak pygmy swellshark (C. sarawakensis) inscientific literature.
Voracious and opportunistic in feeding habits, the blotchy swellshark is known to consume numerous types offishes andinvertebrates, including an unusually high diversity ofcartilaginous fishes. Like otherCephaloscyllium species, it is capable of rapidly inflating its body as a defense against predators. This species isoviparous, with females layingencapsulated eggs two at a time. There is no well-definedbreeding season and reproduction occurs year-round. The eggs hatch after approximately one year. The blotchy swellshark is harmless and fares well in captivity. It is caught asbycatch incommercialbottom trawls, though its population does not seem to have suffered from fishing activity.
AmericanichthyologistsDavid Starr Jordan andHenry Weed Fowler described the blotchy swellshark in a 1903 volume ofProceedings of the United States National Museum, based on a 98 cm (39 in) longstuffed dry skin originally obtained fromNagasaki, Japan. They gave it thespecific epithetumbratile (from theLatinumbratilis, meaning "shaded") and assigned it to thegenusCephaloscyllium.[3]
Thetaxonomy of the blotchy swellshark has a history of confusion.[4] Theholotype dried skin could not be located when shark expertStewart Springer prepared his 1979 review of the catsharks, and in its absence hesynonymizedC. umbratile withC. isabellum on the basis of "inconclusivemorphometric differences".[5] Some authors followed Springer's judgment while others, particularly in Japan, preferred to keep referring toC. umbratile.[6] The taxonomy of this species was further muddled by the application of the nameC. umbratile to a similar but smaller species sharing part of its range. This second species, once referred to as "pseudo-umbratile" byLeonard Compagno, has since been identified asC. sarawakensis. Recently, the holotype was found again, and in 2008Cephaloscyllium umbratile was re-described as distinct fromC. isabellum by Jayna Schaaf-Da Silva and David Ebert.[4]
The blotchy swellshark is known to inhabit the northwesternPacific Ocean fromHokkaido,Japan southward toTaiwan, including theYellow Sea.[7] Its range may extend as far asNew Guinea.[1] This abundant species is abottom-dweller that inhabits rockyreefs on thecontinental shelf, at depths of 90–200 m (300–660 ft).[6][8]
The maximum reported length of the blotchy swellshark is 1.4 m (4.6 ft).[8] It has a firm, stout body with a soft, distensible abdomen, and a short, broad, flattened head. The snout is proportionately long and rounded, with large nostrils divided by short, triangular flaps of skin in front. The small, horizontally oval eyes are placed high on the head and equipped with rudimentarynictitating membranes (protective third eyelids). A tinyspiracle lies closely behind each eye. Behind the spiracle are five pairs ofgill slits, which are short and become progressively smaller posteriorly. The capacious mouth forms a broad arch, and lacks furrows at the corners. The small teeth have a central cusp flanked by a smaller cusplet on both sides. There are around 59tooth rows in the upper jaw and 62 tooth rows in the lower jaw.[4][7]
Thepectoral fins are moderately large and wide, with rounded tips. Thedorsal fins have rounded apexes and are placed well back on the body, the first originating behind the midpoints of the smallpelvic fins. The first dorsal fin is about twice as high as the second. Theanal fin is nearly as large as the first dorsal fin and placed slightly ahead of the second dorsal fin. Thecaudal fin is large and broad, with the upper lobe longer than the lower and bearing a prominent ventral notch near the tip. The skin is thick and sparsely covered by large, well-calcifieddermal denticles; each denticle has a diamond-shaped crown with three horizontal ridges. This shark is cream-colored with dark brownish to grayish mottling on the back and sides, and seven dark brown dorsal "saddles" on the body and tail. The mottling intensifies with age, while the saddles fade and may become obscured. Older sharks may also have a dark blotch on either side between the pectoral and pelvic fins. The underside is pale, with scant darker marks.[4][7]
Like other members of itsgenus, when threatened the blotchy swellshark is capable of rapidly inflating itsstomach with water or air. This allows the shark to wedge itself inside a rocky crevice, becoming extremely difficult to remove.[9] This species is an opportunistic, highly voraciouspredator; one recorded female 1 m (3.3 ft) long had 10 fish about 20 cm (7.9 in) long and 15 squid about 15 cm (5.9 in) long in her stomach. Predominantlypiscivorous, this species is known to prey uponhagfish and at least 50 species ofbony fishes, including fast-swimming types that inhabit open water; significant prey species include themackerelScomber japonicus, thesardineSardinops melanostictus, thefilefishThamnaconus modestus, and thehakelingPhysiculus japonicus. Unusually for such a small shark, it also feeds on at least 10 species ofcartilaginous fishes, includinglantern sharks,catsharks (particularly thecloudy catshark,Scyliorhinus torazame, and its eggs), theelectric rayNarke japonica, andskates (including their eggs). It alsocannibalizes smaller members of its own species.Cephalopods, mostly thesquidDoryteuthis bleekeri and thecuttlefishSepia spp., are also frequently taken, whilecrabs,shrimp, andisopods are occasionally consumed.[6] The dietary composition of juveniles varies notably from place to place.[10]
The blotchy swellshark isoviparous, and reproduction proceeds throughout the year with no obvious seasonal cycling. Adult females have a single functionalovary, on the right, and two functionaloviducts. The species is thought to be relatively prolific, as the ovary contains numerousova at various stages of development. Pairs of eggs are laid at a time, one per oviduct.[6] Females have been documented producing eggs even after years without male contact, suggesting that they may be able to storesperm.[11] The purse-shapedegg capsules are relatively large and thick, measuring around 12 cm (4.7 in) long and 7 cm (2.8 in) across. The capsule surface is smooth with lengthwise striations, and opaque cream in color with yellow margins. Long, coiled tendrils extend from the four corners of the capsule. When theembryo is 11 cm (4.3 in) long, theexternal gills have been lost, thedermal denticles have begun to develop, and light brown saddles are present.[7] The eggs take roughly one year to hatch; newly emerged sharks measure 16–22 cm (6.3–8.7 in) long.[8] From a series of captive rearing experiments, Sho Tanaka reported that hatchling sharks grew in length by up to 0.77 mm (0.03 in) per day.[12] Males and females attainsexual maturity at the size of 86–96 cm (34–38 in) and 92–104 cm (36–41 in) respectively; the growth rate after maturity is very low.[6] Knownparasites of this species include thenematodePorrocaecum cephaloscyllii,[13] and theleechStibarobdella macrothela.[14]
Harmless to humans, the blotchy swellshark adapts readily to captivity and has reproduced inpublic aquariums.[8] This species iscaught incidentally by Japanese and Taiwanesebottom trawlers and brought to market. Intensivecommercial fishing within its range do not yet appear to have impacted its numbers. TheInternational Union for Conservation of Nature (IUCN) has listed it asNear Threatened.[1]
