Marine Wildlife
Fact sheets
Threatened Marine Species found in NT Waters
The following information is taken from Lost from our landscape: threatened species of the Northern Territory edited by John Woinarski, Chris Pavey, Raelee Kerrigan, Ian Cowie and Simon Ward. A full list of Threatened Marine Species in the NT is available on the Wildlife Threatened Species webpage.
Speartooth shark or Bizant river shark
The speartooth shark is a medium-sized whaler shark that grows to 2 to 3 m. The dorsal surface is grey and the ventral surface paler, with an inconspicuous pale stripe on the flanks. It has a short, broadly rounded snout and small eyes. The
dorsal fins are similar in size and the anal fin is about the same size as the second dorsal fin (Last and Stevens 1994).
The Wenlock River (west coast of Cape York Peninsula) population of Glyphis sp. A differs in pectoral fin colour from the Northern Territory specimens (H.K. Larson pers. obs.; S. Peverell pers. comm.) but the significance of this is unknown. The taxonomic status remains uncertain. Together with specimens from New Guinea this species may be synonymous with the more wide-ranging Glyphis glyphis.
Barramundi gill netting and recreational fishing are threatening processes in the Northern Territory, as is the capture of juveniles for crab-pot bait.
Northern river shark
The northern river shark is similar to the more common bull shark that occurs in similar habitats and range. However, this species is a steely-grey colour and may be longer than 2 m. The northern river shark also has a triangular first dorsal fin, and a second dorsal fin that is two thirds the height of the first dorsal fin. Its small eye is located in the grey shaded part of the head (Last and Stevens 1994).
Potential threatening processes in Northern Territory waters include recreational fishing and barramundi gill netting. There may be some use of juveniles as bait for crab fisheries (H. Larson pers. comm.).
Dwarf sawfish
The dwarf sawfish is a small, robust shark-like sawfish that grows to at least 1.4 m. The rostrum (snout) is broad and bears 18 to 22 pairs of lateral teeth starting from the base, and equally spaced. Nostrils behind the eyes are broad with large nasal flaps. The body is usually greenish-brown above and white ventrally. The pectoral fins are broadly
triangular with broad bases and the dorsal fins are tall and pointed with the first dorsal fin positioned over or just forward of the pelvic fin origin. The lower lobe of the caudal fin is small and the posterior margin of the caudal fin almost straight (Last and Stevens 1994).
Populations have been significantly reduced as a result of by-catch in commercial gill net and trawl fisheries (Pogonoski et al. 2002). Recreational fishing may also affect the species. Elsewhere, sawfish generally have also been affected by habitat degradation (Cavanagh et al. 2003).
Freshwater sawfish
The freshwater sawfish is a medium-sized sawfish with a body length up to 3 m although reputed to reach up to 7 m. The body is yellowish, slender and shark-like with a blade-like rostrum (snout) bearing 18 to 23 pairs of lateral teeth. The teeth start near the rostrum base, and are equally spaced. Like other rays, it has gill openings (five) on the ventral surface of the head. The body is yellowish to greyish with a white ventral surface. Pectoral fins are broadly triangular with broad bases and dorsal fins tall and pointed with the first dorsal fin positioned well forward of the pelvic fin origin. The lower lobe of the caudal fin is small and the posterior margin of the caudal fin concave (Last and Stevens 1994).
The impact of fishing practices in the Northern Territory on freshwater sawfish is largely unknown. Increasing development, resulting in degradation of riverine habitat, may also threaten the species.
Green sawfish
The green sawfish is a large, robust shark-like sawfish growing to a length of 5 m, with some reports to 7.3 m. The rostrum (snout) is slender with 24 to 34 pairs of lateral teeth. The teeth are present on the basal quarter of the blade becoming much closer together toward the tip. The body is greenish-brown or olive above and whitish below, and the skin is rough. The pectoral fins are broadly triangular with broad bases and dorsal fins tall and pointed with the first dorsal fin positioned slightly behind the pelvic fin origin. The lower lobe of the caudal fin is small and the posterior margin of the caudal fin almost straight (Last and Stevens 1994).
Incidental capture in commercial prawn and fish trawling and gill-netting are threatening processes (Last and Stevens 1994; Stobuzki et al. 2002). In some areas, targeted fishing may also threaten the species as the flesh is acceptable in the dried fish trade (Grant 1978). Fishing appears to have led to the decline of the species in southern states (Johnson 1999).
