| Cloudy catshark | |
|---|---|
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Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Division: | Selachii |
| Order: | Carcharhiniformes |
| Family: | Scyliorhinidae |
| Genus: | Scyliorhinus |
| Species: | S. torazame |
| Binomial name | |
| Scyliorhinus torazame (S. Tanaka (I), 1908) | |
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| Range of the cloudy catshark[2] | |
| Synonyms | |
Catulus torazameTanaka, 1908 | |
Thecloudy catshark (Scyliorhinus torazame) is a commonspecies ofcatshark, belonging to thefamilyScyliorhinidae. It is abottom-dweller that inhabits rockyreefs in the northwesternPacific Ocean, from the shore to a depth of 320 m (1,050 ft). Growing up to 50 cm (20 in) long, this small, slim shark has a narrow head with a short blunt snout, no grooves between the nostrils and mouth, and furrows on the lower but not the upper jaw. It is also characterized by extremely rough skin and coloration consisting of a series of dark brown saddles along its back and tail, along with various darker and lighter spots in larger individuals.
The diet of the cloudy catshark consists ofmolluscs,crustaceans, andbony fishes. It isoviparous, with females layingencapsulated eggs two at a time in nursery areas. Theclaspers of the male bear numerous hooks that likely serve to facilitatecopulation. This harmless shark can be readily maintained in captivity and is used as amodel organism for biological research. It iscaught incidentally, and generally discarded, bycommercial fisheries. These activities do not appear to have negatively affected its population, leading it to be listed underLeast Concern by theInternational Union for Conservation of Nature (IUCN).
The original description of the cloudy catshark was published in 1908 byShigeho Tanaka in theJournal of the Faculty of Science, University of Tokyo. He gave it thespecific epithettorazame, which is its Japanese name (虎鮫, literally "tiger shark"), and assigned it to the genusCatulus. Thetype specimen was a 45 cm (18 in) long adult male caught offMisaki, Kanagawa,Japan.[3] Subsequent authors havesynonymizedCatulus withScyliorhinus.[4]
The cloudy catshark reaches 50 cm (20 in) long and has a thin, deep, and firm body. The narrow head makes up slightly under one-sixth of the total length, and is two-thirds as wide as it is long. The snout is short and rounded. The large nostrils are preceded by small, triangular flaps of skin that do not reach the wide mouth. The medium-sized eyes are horizontally oval, equipped with rudimentarynictitating membranes (protective third eyelids), and followed by moderatespiracles. There are no grooves between the nostrils and the mouth. There are furrows extending from the corners of the mouth over the lower jaw only. The small teeth have a long central cusp typically flanked by two pairs of cusplets. The five pairs ofgill slits are short, with the fourth pair over thepectoral fin origins.[4][5]
The twodorsal fins are placed towards the back of the body, with the first originating over the rear of thepelvic fin bases. The first dorsal fin has a rounded apex and is larger than the second dorsal fin, which has a more angular shape. The pectoral and pelvic fins are moderate in size. In males, the inner margins of the pelvic fins are merged to form an "apron" over the long, cylindricalclaspers. The origin of theanal fin lies approximately between the dorsal fins. Thecaudal peduncle is about as deep as the body, and leads to a lowcaudal fin with an indistinct lower lobe and a ventral notch near the tip of the upper lobe. The skin is thick and very rough due to thedermal denticles, which are large and upright with three backward-pointing teeth. This species is brown on the back and sides, with 6–10 indistinct darker dorsal saddles, and plain yellowish on its ventral side. Larger sharks also have many large, irregularly shaped light and dark spots.[4][5]
The cloudy catshark is common in the northwestern Pacific offJapan,Korea,China, and possibly thePhilippines.[2]Bottom-dwelling in nature, this species can be found from the shore out to a depth of 320 m (1,050 ft) on thecontinental shelf and uppercontinental slope.[1] It favors rocky reefs and does not appear to bemigratory.[6]
The cloudy catshark feeds primarily onmolluscs, followed bycrustaceans andbony fishes.[7] Apredator of both this shark and itsegg cases is theblotchy swell shark (Cephaloscyllium umbratile).[8] A knownparasite of this species is themyxosporidianChloromyxum scyliorhinum.[9] Reproduction isoviparous; adult females have a single functionalovary and two functionaloviducts.[5] As a prelude tomating, the male bites at the female's pectoral fin, side, and gill region. Once he has a grip, he wraps his body around hers and inserts one of his claspers into hercloaca.Copulation may last between 15 seconds and 4 minutes.[10] The claspers of the male are unusual in that each has a row of around a hundred hooks running along the inner margin. These hooks likely serve to anchor the male to the female during copulation.[11] The female is capable of storingsperm within hernidamental gland (an organ that secretes egg cases) for many months.[12]
Females produce two matureeggs at a time, one per oviduct. The eggs are enclosed in smooth, translucent yellow, vase-shaped capsules measuring 1.9 cm (0.75 in) across and 5.5 cm (2.2 in) long. There are long tendrils at the four corners of the capsule. The eggs are laid in defined nursery areas: One such area is located at a depth of 100 m (330 ft) offHakodate. When theembryo is 3.6 cm (1.4 in) long, it has external gills, undeveloped fins, and no pigmentation. At an embryonic length of 5.8 cm (2.3 in), the external gills have all but disappeared, and a covering of small denticles is present. By a length of 7.9 cm (3.1 in), the embryo has well-developed fins and pigmentation, and generally resembles the adult.[5] The eggs take 15 months to hatch at 11.3 °C (52.3 °F), and 7–9 months to hatch at 14.5 °C (58.1 °F).[6] The newly hatched shark measures 8 cm (3.1 in) long or more.[4] Maturation size tends to increase with decreasing water temperature: Off northerly Hakodate, both sexes mature at over 38 cm (15 in) long, while some females remain immature even at 47 cm (19 in) long. By contrast, off southerlyTsushima Island both sexes mature at around 33 cm (13 in) long.[5][13] Themaximum lifespan is at least 12 years.[6]
Harmless to humans, the cloudy catshark adapts well to captivity and has reproduced in the aquarium.[6] It is often used as amodel organism inphysiology research.[14][15] On September 25, 1995, Masuda Motoyashi and colleagues used this species to perform the first successfulartificial insemination of ashark or ray.[12] The cloudy catshark iscaught incidentally bycommercial fisheries with bottomfishing nets includingtrawls andgillnets, as well as on bottomlonglines. Captured individuals are typically discarded, possibly with a high survival rate due to their hardiness. Some 40% of the fish discarded inYamaguchi Prefecture fisheries are of this species.[1] The bottom trawl fishery operating offFukushima Prefecture may catch over a ton of cloudy catsharks annually, which are also discarded.[16]
Despite heavy fishing pressure within its range, the cloudy catshark remains common, perhaps because it may be morebiologically productive than most other sharks. As a result, it has been assessed asLeast Concern by theInternational Union for Conservation of Nature (IUCN).[1] Cloudy catsharks from a number of locations off Japan have been found to be contaminated withpolychlorinated biphenyls (PCBs) anddichlorodiphenyldichloroethylene (DDEs), which theyacquire from their food. One likely source of thesepollutants is the use of thepesticideDDT bydeveloping nations in southern Asia.[17]
