| Australian swellshark | |
|---|---|
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Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Division: | Selachii |
| Order: | Carcharhiniformes |
| Family: | Scyliorhinidae |
| Genus: | Cephaloscyllium |
| Species: | C. laticeps |
| Binomial name | |
| Cephaloscyllium laticeps (A. H. A. Duméril, 1853) | |
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| Range of the Australian swellshark | |
| Synonyms | |
Cephaloscyllium nascioneWhitley, 1932 | |
TheAustralian swellshark (Cephaloscyllium laticeps) ordraughtboard shark, is aspecies ofcatshark, and part of thefamilyScyliorhinidae,endemic to southernAustralia. Thisbottom-dwelling species can be found on thecontinental shelf down to a depth of 220 m (720 ft). Usually measuring 1 m (3 ft 3 in) long, it is a stout-bodied, broad-headed shark with a short tail and a firstdorsal fin much larger than the second. It can be identified by its variegated dorsal coloration of brown or grey patches and numerous spots.
Australian swellsharks are sedentary and mainlynocturnal, with most individuals remaining within the same local area throughout the year. It feeds on smallcrustaceans,cephalopods, andfish. When threatened, it responds by rapidly taking in water or air to inflate its body, hence the name "swellshark". This shark isoviparous and females lay pairs of distinctively ridgedegg capsules at 20- to 30-day intervals. The eggs hatch after 11–12 months. Harmless and of littlecommercial interest, many Australian swellsharks arecaught incidentally ingillnets andbottom trawls but usually survive to be released because of their extreme hardiness. As a result, theInternational Union for Conservation of Nature (IUCN) has assessed this species as ofLeast Concern.
The first scientific description of the Australian swellshark, asScyllium laticeps, was published in 1853 by FrenchzoologistAuguste Duméril, in thescientific journalRevue et Magasin de Zoologie. Thetype specimen was a 79-centimetre-long (31 in) male caught offTasmania.[2] Thespecific epithetlaticeps is derived from theLatinlatus, meaning "broad", with the suffixceps, meaning "head".[3] Othercommon names for this species include flopguts (a reference to its ability to inflate),[4] Isabell's swell shark, nutcracker shark, rock shark, sleepy Joe, and spotted swellshark.[5] This species is almost identical to thedraughtsboard shark (C. isabellum) ofNew Zealand; the two species differ in coloration and the form of their egg cases (ridged inC. laticeps versus smooth inC. isabellum).[2]
The Australian swellshark has a stocky, rounded body that tapers significantly to the shortcaudal peduncle. The head comprises no more than a fifth of the total length and is broad and moderately flattened, with a very short, thick, blunt snout. Thenostrils are divided into small incurrent and excurrent openings by short, triangular flaps of skin that do not reach the mouth. The mouth is extremely large, without furrows at the corners. The teeth are numerous and small with multiple cusps; the upper teeth are exposed when the mouth is closed. The large, oval eyes are placed somewhat on the upper surface of the head, and have rudimentarynictitating membranes (protective thirdeyelids) and ridges underneath.[2][3]
There are twodorsal fins, the first much larger than the second. The first dorsal originates over the forward half of thepelvic fin bases, while the second is located over theanal fin. Thepectoral fins are large and broad, and the anal fin is larger than the second dorsal fin. The short and broadcaudal fin has an indistinct lower lobe and a prominent ventral notch near the tip of the upper lobe. The skin is thick and covered by well-calcified,arrowhead-shapeddermal denticles, which are more sparse in young sharks.[2][3] The back and sides are light grey to brown, with an irregular pattern of close-set darker saddles and blotches along with many dark (sometimes light) spots, and a dark stripe from under the eye to the pectoral fin origins. The fins do not have sharply lighter margins. The underside is cream-coloured, with some mottling on the fins and often a dark stripe running down the middle in adults.[6] The maximum known length is 1.5 m (4 ft 11 in), though few exceed 1.0 m (3 ft 3 in).[3]
The Australian swellshark inhabits the continental shelf of southern Australia, from theRecherche Archipelago offWestern Australia toJervis Bay inNew South Wales, including Tasmania.[1] It is commonly found on or near the bottom amongst rockyreefs orseaweed beds, from close to shore to a depth of 220 m (720 ft).[2][7]
The most abundant catshark species in the coastal waters of southern Australia, the Australian swellshark is a generally sluggish swimmer that is more active at night. During the day, it is often found resting singly or in groups under ledges or inside caves. Tracking studies have shown that some individuals are continuously active for months at a time, while others alternate activity with periods of stationary rest lasting up to five days. Most Australian swellsharks present within a given region tend to remain there year-round, frequenting established feeding areas or preferred habitats. On the other hand, a minority of sharks have been recorded covering distances of up to 300 km (190 mi).[4][8] This extremely hardy species can survive for more than a day out of water.[9]
One of the higher-levelpredators within itsecosystem, the Australian swellshark feeds oncrustaceans (particularlycrabs androck lobsters),cephalopods (includingsquid andoctopus), and smallfishes. Even large-sized prey tends to be swallowed whole; the long periods of rest exhibited by some sharks may relate todigestion.[2][8] Like the other members of its genus, this shark is capable of rapidly inflating its body by taking water or air into itsstomach, as a defense againstpredators. These include larger fishes, such as thebroadnose sevengill shark (Notorynchus cepedianus), andmarine mammals. By inflating, the shark may be able to wedge itself inside crevices, make itself harder to swallow, or simply intimidate a would-be predator.[4]Marine snails are known to prey upon this shark's eggs. The Australian swellshark serves as a host to a number ofparasite species, but these are poorly documented.[3]
The Australian swellshark isoviparous. Males have larger teeth than females, with which to bite and hold onto them forcopulation.[4] Whether there is a specificmating season is uncertain, though in terms ofsperm production males are capable of breeding year-round. Females have a single functionalovary and twooviducts,ovulating a single egg into each at a time. They can store sperm for at least 15 months. Females produce eggs throughout the year, laying them in pairs approximately once every 20 days from January to June, and once every 30 days the rest of the year. The second egg in a pair is deposited 12–24 hours after the first.[4][8]
The pale, flask-shapedegg capsules measure 13 cm (5 in) long and 5 cm (2 in) across, and bear 19–27 crosswise ridges. There are long, curling tendrils at the four corners, which allow the female to attach the capsule to seaweed or other bottom structures.[3] In captivity, theembryo develops external gills at two months old, which are retained until it is five months old, at which time the internal gills take over and the firstpigmentation appears. At six months, embryonic growth accelerates and theyolk sac begins to shrink, disappearing by nine to ten months of age. Hatching usually occurs at eleven to twelve months; the newly emerged young are miniature versions of the adults measuring 14 cm (6 in) long.[4][8] Malesmature sexually at a length of 71–87 centimetres (28–34 in), and females at 75–86 centimetres (30–34 in).[8]
The Australian swellshark is harmless to humans and seldom utilised, though recently in parts of Tasmania some have begun to be marketed as a source of "flake".[1][8] It is regarded as a nuisance bylobster fishers due to its habit of enteringtraps to eat the contents.[3] Every year, substantial numbers of Australian swellsharks are caught asbycatch in the southeast Australian sharkgillnet fishery, and more inbottom trawls and onlonglines.[8] These animals are usually released, and likely suffer minimal mortality due to their resilience. Since this species at present faces little risk from fisheries, theInternational Union for Conservation of Nature (IUCN) has listed it underLeast Concern. Althoughcommercial fisheries reported drops in Australian swellshark catches from 1973 to 1976 and 1998 to 2001, these appeared to have resulted from changing fishing habits rather than actual population declines.[1] Nevertheless, as a precaution the government of Tasmania has instituted a possession limit of two sharks per person or five sharks per boat per day.[8]
