australian weasel shark
Small and abundant shark in northern Australia
The Australian Weasel shark (Hemigaleus australiensis) is an uncommon species of ground shark in the family Hemigaleidae. It inhabits shallow waters off northern Australia to a depth of 560 feet.
Family: Hemigaleidae – Weasel sharks
Common Name– Ground Sharks
Common Name– Weasel Sharks
Status: IUCN Red List LEAST CONCERN
Average Size and Length: The Australian Weasel shark reaches a length of 3.6 feet.
Teeth and Jaw: The Australian Weasel shark has a short, curved mouth with prominent furrows at the corners. There are 28–30 upper and 46–52 lower tooth rows, which are not visible when the mouth is closed; the upper teeth are broad and angled with large serrations on the trailing edge only. The lower teeth are thin and upright with smooth edges.
Head: It has a long head with a thick rounded snout. Its eyes are oval with nictitating membranes. They have notched posterior rims, and tiny spiracles behind and above the eyes. The nostrils are large with skin flaps.
Denticles: The dermal denticles are small and overlapping. Each one has five horizontal ridges leading to marginal teeth.
Tail: The caudal peduncle has a crescent-shaped notch at the upper origin of the caudal fin. The asymmetrical caudal fin has a well-developed lower lobe and a long, narrow upper lobe with a ventral notch near the tip.
Demographic, Distribution, Habitat, Environment and Range: The Australian Weasel shark can be found around continental and insular shelves off northern Australia, from Geraldton in Western Australia to Brunswick Heads in New South Wales. They tend to swim close to the sea floor and can be found from inshore waters down to 560 feet deep. Juveniles and small adults are generally found in sandy areas with seagrass cover, while large adults can be found more around coral reefs.
Diet: The Australian Weasel shark feeds mainly on octopuses either swallowing them whole or removing the arms first. Octopuses become increasingly important to its diet with age, sharks over 35 inches long eat octopus almost exclusively.
Bobtail squids represent a minor secondary food source, particularly for smaller sharks. In addition, other cephalopods, mud lobsters, crabs, and echinoderms are seldom eaten.
Australian Weasel sharks most likely hunt at dawn and at dusk probing for bottom-dwelling prey. On occasion they will take food from the water column (for instance seasonal squid aggregations).
Aesthetic Identification: The Australian Weasel shark has a slender spindle-shaped body. It is light grey to bronze above, darkening at the tips of the second dorsal fin and upper caudal fin lobe (may be unclear in larger sharks), and counter-shaded pale below. The underside is off-white, and the first dorsal fin has a pale trailing margin. There are five pairs of short gill slits.
All the fins of the Australian Weasel shark, particularly the narrow pectoral fins, are falcate. The medium-sized first dorsal fin originates just behind the pectoral fin rear tips. The second dorsal fin is about two-thirds as tall as the first, and there is no midline ridge running between them. The pelvic fins are broad and slightly larger than the anal fin. The anal fin has a solid notch in the trailing margin and is positioned slightly behind the second dorsal fin. The prominent lateral line curves downward below the second dorsal fin.
Biology and Reproduction: Known parasites of the Australian Weasel shark include tapeworms and copepods.
The Australian Weasel shark is viviparous. The gestation period is 6 months and typically 2 litters are produced annually (February and September). Litter size varies from 1 to 19 pups, but the average is 8). The embryos lose their external gills at a length of 5.1 inches. They develop coloration by a length of 9.1 inches. They are born at a length of 12 inches. Males and females reach sexual maturity at approximately 24 and 26 inches long.
Behavioral Traits, Sensing and Intelligence: Young sharks transitioning to adulthood shift from sea grass habitats, to coral reef habitats.
Australian Weasel Shark Future and Conservation: The Australian Weasel shark is commonly caught by prawn and fish trawlers operating off northern Australia. Smaller numbers are also captured in gillnets and on longlines. They are resilient to fishing trends.
Australian Weasel Shark Recorded Attacks on Humans: Not a threat to humans.