AUSTRALIAN SWELLSHARK

Taxonomy:

Phylum– Chordata

Class– Chondrichthyles

Order– Carcharhiniformes

Common Name– Ground Sharks

Family– Scyliorhinidae

Common Name– Catsharks

Genus– Cephaloscyllium

Species– laticeps

Status: IUCN Red List LEAST CONCERN

Average Size and Length: An egg case measures 13×5 cm. Hatchlings measure around 14 cm/5.5 inches. Mature males measure around 82 cm/2.7 feet, and the maximum recorded is greater than 100 cm/3.3 feet.

Current Rare Mythical Sightings: The first scientific description of the Australian swellshark, as Scyllium laticeps, was published in 1853 by French zoologist Auguste Duméril, in the scientific journal Revue et Magasin de Zoologie. The type specimen was a 79 cm/2.6 feet long male caught off Tasmania. The specific epithet laticeps is derived from the Latin latus, meaning “broad”, with the suffix ceps, meaning “head”.

Teeth and Jaw: 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. Males have larger teeth than females, with which to bite and hold onto them for copulation. Upper jaw teeth 38/38, lower jaw teeth 27/27.

Head: 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. The nostrils are divided into small incurrent and excurrent openings by short, triangular flaps of skin that do not reach the mouth. The large, oval eyes are placed somewhat on the upper surface of the head, and have rudimentary nictitating membranes. There are ridges over the eyes.

Denticles: The skin is thick and covered by well-calcified, arrowhead-shaped dermal denticles, which are sparser in young sharks.

Tail: The caudal peduncle is short. The short and broad caudal fin has an indistinct lower lobe and a prominent ventral notch near the tip of the upper lobe.

Demographic, Distribution, Habitat, Environment and Range: The Australian swellshark can be found in southern Australia from the Recherche Archipelago off Western Australia to Jervis Bay in New South Wales, including Tasmania, inshore on the continental shelf to at least 197 feet, possibly down to 722 feet.  They are considered demersal, and reef-associated.

Diet: They feed on small reef fish, crustaceans and squid. Large-sized prey tends to be swallowed whole; the long periods of rest exhibited by some sharks may relate to digestion.

Predators include the Broadnose Sevengill shark (Notorynchus cepedianus), other larger fish and marine mammals.

Marine snails are known to prey upon this shark’s eggs.

Aesthetic Identification: The Australian swellshark is almost identical to the Draughtsboard shark (C. isabellum) of New Zealand; the two species differ in coloration and the form of their egg cases, which are ridged in C. laticeps versus smooth in C. isabellum. The Australian swellshark is apparently synonymous with Cephaloscyllium nascione, the Whitefinned swellshark.

The Australian swellshark has a stout, rounded body, and a strongly variegated pattern of dark brown or greyish close-set dark saddles and blotches, many dark spots, and occasional light spots on a lighter grey or chestnut background. There is a broad dark stripe between the eye and pectoral origin and dark below the eyes. The ventral side is cream, usually with a broad stripe down the belly in adults. There are no conspicuous light fin margins. They have an inflatable stomach. There are two dorsal fins, the first much larger than the second. The larger first dorsal fin originates over the pelvic fin bases. The second dorsal fin originates over the anal fin. The pectoral fins are large and broad, and the anal fin is larger than the second dorsal fin.

Biology and Reproduction: Their stomachs inflate. Vertebrae count is between 110-116, precaudal is 76-81.

They are oviparous, and lay rigid (in a crosswise pattern) cream colored egg cases, which they attach to seaweed and benthic invertebrates. They have 19–27 crosswise ridges. The slits in the egg case allow water to flow through the egg case where the embryo will continue to develop until it hatches. There are long, curling tendrils at the four corners.

Whether there is a specific mating season is uncertain, though in terms of sperm production males are capable of breeding year-round. Females have a single functional ovary and two oviducts, 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. The eggs hatch after 11–12 months.

In captivity, the embryo 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 first pigmentation appears. At six months, embryonic growth accelerates and the yolk 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. Males mature sexually at a length of 71–87 cm/2.3-2.9 feet, and females at 75–86 cm/2.5-2.8 feet.

The Australian swellshark serves as a host to a number of parasite species.

Behavioral Traits, Sensing and Intelligence: The Australian swellshark can inflate its stomach with air or water in an effort to scare potential predators.

They are mainly nocturnal. Most individuals remain within the same local area throughout the year.

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 miles. (Awruch, C.A. (2007). “The reproductive biology and movement patterns of the draughtboard shark, (Cephaloscyllium laticeps): implications for bycatch management“. Ph.D. thesis, University of Tasmania, Australia.)

They can survive for more than a day out of water.

Speed: 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.

Australian Swellshark Future and Conservation: They are of least concern. They are discarded as bycatch from shark gill net fisheries. They are resilient and do survive bycatch well. They are more recently marked as a source of flake, and are actually considered a nuisance by lobster fishers.

Although commercial 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. As a precaution the government of Tasmania has instituted a possession limit of two sharks per person or five sharks per boat per day.

Australian Swellshark Recorded Attacks on Humans: Not a threat to humans.