IUCN threat status:

Endangered (EN)

Habitat

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Habitat and Ecology

Habitat and Ecology
The Dwarf Sawfish is a shallow-water coastal and estuarine sawfish occurring on sand and mud flats, although it also occasionally penetrates upstream into rivers and has been recorded in salinities of 1–41 ppt (Thorburn et al. 2008). There is one record from over 100 km upstream in the Victoria River, Northern Territory at a salinity of 9.7 ppt (Thorburn et al. 2003). Thorburn et al. (2008) documented Dwarf Sawfish in 0.7–7 m depth, while Stevens et al. (2008) recorded an individual reaching a maximum depth of 20 m. Reports of Dwarf Sawfish (i.e., Morgan et al. 2011 erroneously citing Stephenson and Chidlow 2003) occurring in offshore waters are unsubstantiated.

Dwarf Sawfish reach at least 318 cm total length (TL), with males maturing at about 255–260 cm TL and a size at birth estimated at 60–81 cm TL (Peverell 2005, Peverell 2008, Stevens et al. 2008, Last and Stevens 2009, Morgan et al. 2011). Based on annuli in vertebrae, Thorburn et al. (2008) estimated that individuals ~90 cm TL were one year old, 110–120 cm TL were ~2 years old, and ~160 cm TL were ~3 years old. Peverell (2008) estimated longevity of 34 years for Dwarf Sawfish, and an age at maturity of eight years for males. Life table models based on Dwarf Sawfish biological data from the Gulf of Carpentaria indicate an intrinsic rate of population increase of approximately 0.10 yr-1, a population doubling time of 7.2 years and generation time of 16.4 years (Moreno Iturria 2012).

Like other sawfishes, the Dwarf Sawfish is viviparous, with pupping thought to be during the northern Australian wet season (roughly November to April) (Peverell 2005). Litter size of the Dwarf Sawfish is unknown (Last and Stevens 2009), but is assumed to be similar to other Pristis species (for example Largetooth Sawfish P. pristis, range 1–13, mean 7.3 pups per litter; Thorson 1976). Estuarine waters have been suggested to be nursery areas for the species, with juveniles remaining for at least three years (Thorburn et al. 2008).

A movement study with acoustic telemetry in Western Australia revealed that Dwarf Sawfish occupy a restricted area of habitat within a few kilometres of the coast, resting during the high tide in inundated mangrove forests, and moving out onto the subtidal mudflats at low tide (Stevens et al. 2008). Tracked individuals occupied shallow depths of 0–2 m, moving up to 10 km during each tidal cycle. Individuals often returned to within 100 m of previous high tide resting sites, demonstrating the repeated use of habitat (Stevens et al. 2008). This site fidelity was also found for Dwarf Sawfish tagged and recaptured over a three month period in Port Musgrave in the Queensland Gulf of Carpentaria. Those animals occupied shallow sand and mud habitats less than 2 m deep in the estuarine Ducie River and along the coast at the entrance to Port Musgrave (Peverell et al. 2009).

Systems
  • Marine

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Source: IUCN

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