The Australian swellshark or draughtboard shark is the most abundant catshark found in southern Australia. It is known by many names, such as flopguts, Isabell’s swell shark, nutcracker shark, rock shark, Sleepy Joe, spotted swellshark, and whitefinned swellshark. It is sometimes mistaken for the draughtsboard shark of New Zealand. However, they are two distinct species, differing in their coloration and egg case shapes.
French zoologist Auguste Dumèril first described this species in 1853, using a specimen from Tasmania.
Australian Swellshark Scientific Classification
|Scientific name||C. laticeps|
These sharks grow to a length of 100 cm (3.3 ft), with male sharks averaging 82 cm (2.7 ft) and females 75-86 cm (2.5-2.8 ft). The largest recorded specimen was 150 cm (4.9 ft) long.
This species has a stout, rounded body, a flattened head, and a short, blunt snout. Their nostrils are divided by small triangular flaps, and their big, oval eyes have ridges and nictitating membranes. Their enormous mouths are filled with multiple small-cusped teeth, which are larger in males, to help grab onto females while mating. The teeth in the upper jaw are visible even when the mouth is closed.
They have greyish or chestnut upper bodies, with a mottled pattern of close-set dark saddles and splotches, multiple dark spots, occasional light spots, and a dark stripe extending from below the eye to the pectoral fin. Their thick skin has a layer of calcified, arrow-like dermal denticles, which are more sporadic in juveniles. Their lower half is pale, with a broad stripe through the middle in adults. The fins are occasionally spotted and lack lighter margins.
The pectoral fins are broad and large. The first dorsal is much bigger than the second, originating over the pelvic fins. The second dorsal is above the larger anal fin. The tail is short and broad with a pronounced upper ventral notch and inconspicuous lower lobe.
Where do they live
Map Of The Australian Swellshark’s Habitat
They are endemic to the continental shelves of southern Australia. They occur in Recherche Archipelago in Western Australia, Tasmania, and Jervis Bay in New South Wales. They are bottom-dwelling, inhabiting rocky reefs and seaweed beds at depths of up to 220 m (720 ft), but are more common at 60 m (197 ft).
They primarily consume crustaceans, cephalopods, and reef fish. They usually prey whole and may observe long resting periods to digest larger prey.
This species is oviparous and breeds throughout the year. There is no specific breeding season, with females laying pairs of eggs every twenty days from January to June and once every thirty days from July to December. The eggs cases are cream-colored, with 19-27 ridges crisscrossing the surface. They have four long tendrils used to attach them to seaweed or small invertebrates. They are laid one after the other over twenty-four hours and hatch after 11-12 months. Marine snails commonly eat them.
The embryo develops external gills at two months old, which get replaced by internal gills at five months. From the sixth month, growth accelerates, and the egg sack shrinks, disappearing by 9-10 months. The hatched newborns are miniature adults measuring 14 cm (5.5 in). The males reach sexual maturity at 71-87 cm (2.3-2.9 ft), and females mature at 75-86 cm (2.5-2.8 ft).
This shark gets its name from its unique ability to inflate its body. It fills its stomach with air or water, making itself harder to consume. It can also wedge itself under rock crevices or intimidate predators. This modification helps it defend itself from potential predators, such as the broadnose sevengill shark or marine mammals.
This nocturnal species is sedentary during the day and mostly hunts at night. It rests alone or in groups during the day; studies have shown that some individuals alternate between rest periods and activity. It prefers to hunt in established feeding grounds and will stay in one region all year. However, some specimens were found covering distances of up to 300 km (190 mi).
They share many features with other sharks, such as keen senses, streamlined bodies, and sharp cutting teeth. This extremely tough fish can stay out of water for an entire day.
They are harmless and usually caught as bycatch by longlines and bottom trawlers in the southeast Australian shark gillnet fishery. Most of them get released, and their hardiness contributes to their excellent survival rate. They pose a problem to lobster fisheries due to their habit of eating the contents of the traps. Recently, parts of Tasmania have started utilizing them as a source of “flake.”
The recent drops in catches are likely caused by changing fishing methods rather than population decline. Still, the Tasmanian government has limited the number of catches to five per boat as a precautionary measure. Additionally, the Southern and Eastern Scalefish and Shark Fishery in Australia has undergone restructuring through the buying-back of Commonwealth fishing licenses to help in conservation efforts. The IUCN has thus listed this shark as “Least Concern” or “LC.”