Dean C. Thorburn

Ontogenetic depth partitioning by juvenile freshwater sawfish (Pristis microdon: Pristidae) in a riverine environment

The freshwater sawfish (Pristis microdon) is a critically endangered elasmobranch. Ontogenetic changes in the habitat use of juvenile P. microdon were studied using acoustic tracking in the Fitzroy River, Western Australia. Habitat partitioning was significant between 0+ (2007 year class) and larger 1+ (2006 year class) P. microdon. Smaller 0+ fish generally occupied shallower water ( 0.6 m. Significant differences in hourly depth use were also revealed. The depth that 1+ P. microdon occupied was significantly influenced by lunar phase with these animals utilising a shallower and narrower depth range during the full moon compared with the new moon. This was not observed in 0+ individuals. Habitat partitioning was likely to be related to predator avoidance, foraging behaviours, and temperature and/or light regimes. The occurrence of 1+ P. microdon in deeper water may also result from a need for greater depths in which to manoeuvre. The present study demonstrates the utility of acoustic telemetry in monitoring P. microdon in a riverine environment. These results demonstrate the need to consider the habitat requirements of different P. microdon cohorts in the strategic planning of natural resources and will aid in the development of management strategies for this species.

Mitochondrial DNA supports the identification of two endangered river sharks (Glyphis glyphis and Glyphis garricki) across northern Australia

The river sharks (genus Glyphis) are a small group of poorly known sharks occurring in tropical rivers and estuarine waters across northern Australia, south-east Asia and the subcontinent. The taxonomy of the genus has long been unclear due to very few individuals having been caught and examined, resulting in a paucity of data regarding their distribution, biology and ecology. Only recently has attention focussed on the two Australian species, G. glyphis and G. garricki. This study is a result of a rare opportunity to collate the few samples that have been collected from these species and the bull shark Carcharhinus leucas, which shares an overlapping range. These samples were analysed using the DNA barcoding approach (cox1 mitochondrial gene), compared with six other species of carcharhinids and evaluated in light of the current taxonomic classification. Nine species-specific nucleotide differences were found between G. glyphis and G. garricki and no intra-specific variation provides strong support for the separation into distinct species. Significant differences were also observed at the inter-generic level, with Glyphis forming a distinct clade from Carcharhinus. This study provides the basis for future molecular studies required to better address conservation issues confronting G. glyphis and G. garricki in Australia.

Threatened fishes of the world: Pristis microdon Latham 1794 (Pristidae)

Common names: Freshwater sawfish, Leichhardt’s sawfish, smalltooth sawfish. Conservation status: Endangered (IUCN Red List 2003), vulnerable (Australian Environment Protection and Biodiversity Conservation Act 1999). Identification: Distinguished by first dorsal fin being considerably anterior to pelvic fins, caudal fin has a conspicuous ventral lobe (Compagno & Last 1998). Reputed to attain 700 cm TL. Rostral saw broad with 14–23 teeth on each side (17–23 teeth in Australian waters), butdiffersbetweensexes (17–21 for females and19–23 formales in northern Australia) (Ishihara et al. 1991, Thorburn M Compagno & Last 1998; Wilson 1999), however the only reports of mature animals are from a 360 cm TL mature male from the Oriomo River mouth (New Guinea) (Tanaka 1991) and one mature 300 cm TL male off the northern Pilbara coast (Western Australia), hundreds of kilometres south of the nearest riverine population (Fitzroy River) (Thorburn et al. 2004b). Thirty five of 36 P. microdon captured in Tanaka’s (1991) study from northern Australian and New Guinean fresh and estuarine waters were immature. Similarly, all 30 males (80–230 cm) captured during a study of the Fitzroy River were immature (Thorburn et al. 2004a). It is suggested that rivers may act as nursery grounds. Maturity attained at lengths greater than 240 m (Compagno & Last 1998, Thorburn & Morgan unpubl. data). Threats: Commercial and recreational fisheries and habitat degradation of rivers. Rostral teeth make them extremely vulnerable to nets of all mesh sizes. While protected in Australian

Threatened fishes of the world: Glyphissp. C (Carcharhinidae)

Common names: Northern river shark, northern speartooth shark, New Guinea river shark. Conservation status: Listed as critically endangered under the IUCN Red List 2003 and endangered in Australia under the Environment Protection and Biodiversity Conservation Act 1999. Identification: Glyphis are distinguished from other carcharhinids by the relatively large second dorsal fin which is between one half and three fifths the height of the first (Last & Stevens 1994) and the possession of non-crescentric, longitudinal precaudal pits (Compagno & Niem 1998). Glyphis sp. C is differentiated from Glyphis sp. A and Glyphis sp. B by a lower vertebral count (142–151 cf. 198–217) and lower number of diplospondylous caudal centra (65–68 cf. 85–93) (Compagno & Niem 1998, Thorburn &Morgan 2004). The eye is small, being between 0.77 and 1.03% of the total length (TL). Distribution: Until recently Glyphis sp. C was known only from three specimens from the Fly River in Papua New Guinea, and five specimens from rivers in the Northern Territory of Australia, including two from the Adelaide River, two from the East Alligator River and a pair of jaws from the South Alligator River (Taniuchi et al. 1991, Compagno & Niem 1998, Larson 2000). However, since 2001 the authors have captured 10 in King Sound and its tributaries in the Kimberley region of Western Australia (Thorburn & Morgan 2004). Abundance: Glyphis sp. C is extremely rare with only 18 individuals known to science however it may be more common than previously reported with little survey work being conducted in the remote Kimberley region of northwestern Australia. A high occurrence of spinal deformity (ca. 50%) in the Kimberley (King Sound) population may represent a genetic abnormality associated with inbreeding within a small gene pool (Thorburn & Morgan 2004). Habitat and ecology: Habitats where the species has been captured include highly turbid waters in tropical, macrotidal mangrove creeks (salinities 20–36.6 ppt) (Thorburn & Morgan unpubl. data) and rivers or estuaries (6.1–25.8 ppt) (Larson 2000). Preliminary dietary studies by the authors, using X-ray, demonstrated that in King Sound this species feeds on the lesser salmon catfish, Arius graeffei, and the giant threadfin salmon, Polydactylus macrochir. Reproduction: In the Kimberley region of Western Australia only the largest male captured (1418 mm TL) had fully calcified claspers and was deemed to have attained maturity. The length at maturity of females is not known with the largest female captured (1350 mm TL) being immature. Threats: While fully protected in Australian Commonwealth Waters, which incorporate those marine waters beyond three nautical miles from the low water mark, the species is currently not protected in nearshore and riverine waters inside the three nautical mile limit which falls under State jurisdiction and where they are susceptible to recreational and commercial fishing. Furthermore, many of the individuals captured in the Kimberley are within an area that has been identified as a potential site to be dammed for electricity generation utilising tidal energy. Conservation: Environment Australia is currently reviewing a recovery plan for the conservation of the species in Australian waters. Conservation recommendations: There is an urgent requirement to assess the marine, estuarine and riverine waters of northern Australia, and in particular those within the Kimberley region of Western Australia. It is also necessary for Australian State and Territory Governments to protect this species within those waters that are governed under State or Territory regulations.