|Scientific Name:||Pristis clavata|
|Species Authority:||Garman, 1906|
|Taxonomic Notes:||The Dwarf Sawfish (Pristis clavata) is similar to the Smalltooth Sawfish (Pristis pectinata), with which it may have been previously confused, but it has fewer rostral teeth than the Smalltooth Sawfish (Last and Stevens 2009).|
|Red List Category & Criteria:||Endangered A2cd ver 3.1|
|Assessor/s:||Kyne, P.M., Rigby, C. & Simpfendorfer, C.|
|Reviewer/s:||Pillans, R. & Böhm, M.|
The Dwarf Sawfish (Pristis clavata) is possibly now restricted to tropical waters of northern Australia. Historically, it apparently occurred more widely in the Indian Ocean region and South-East Asia, but there are very few verifiable records from outside of Australia and therefore a great deal of uncertainty regarding its true historical distribution. There have been no confirmed records outside of Australia since the 1800s, although it may still persist in other parts of the Indo-West Pacific. Within Australia, its status on the northeastern coast of Queensland is uncertain with no confirmed records, either recent or historic; its confirmed range is from western Cape York, Queensland, to the northern Pilbara region of Western Australia. It may therefore now have the smallest known distribution of any sawfish species. This is a shallow water coastal and estuarine sawfish occurring on sand and mud flats, with a close association to those adjacent to mangroves. Although it penetrates upstream into rivers it does not regularly occur in freshwater reaches. It reaches at least 318 cm total length but its life history is poorly known. Demographic models demonstrate that population productivity is low. Like other sawfishes, the toothed rostrum and demersal occurrence makes Dwarf Sawfish extremely susceptible to capture in gillnets and demersal trawl nets. Historically, the species has been affected by commercial net and trawl fisheries which operate in inshore areas of its range, the cumulative impacts of which have led to the population decline of this and other sawfish species. The restricted inshore occurrence of Dwarf Sawfish makes it particularly susceptible to capture in commercial gillnet fisheries and observer data has shown that mortality associated with such capture is close to 50% despite a ban on retention.
Despite uncertainty regarding the extent of the species’ wider historical range, it can be considered ‘possibly extinct’ outside of Australia with the disappearance of the species probably occurring outside of the last three generation period (pre-1960s; considering that there are no confirmed records since the 1800s). All sawfish species that occur in Australian waters have undergone significant, albeit largely unquantified, declines, although the current population size and historical abundance of Dwarf Sawfish is unknown. While specific management measures are now in place in Australia, including full species protection, education of fishers about safe release practices, and fishery-specific management, threats are ongoing and there is no information to suggest that the population is recovering from previous declines. Declines of 50-80% are inferred from capture in continuing commercial fisheries, with the Dwarf Sawfish particularly susceptible given its restricted inshore occurrence and relatively limited global range; it is therefore assessed as Endangered. Some remote regions of northern Australia do however have little commercial fishing activities with some relatively small inshore areas closed to commercial fishing. This may provide localised refugia for Dwarf Sawfish, but until such time that viable populations can be verified, it is assumed that the species is continuing to decline, given that threats are ongoing.
The previous assessment for this species was Critically Endangered. However, given the new information that has become available since that last assessment and the fact that the more dramatic declines have happened outside of the three generation period (~49 years), the species now meets the criteria for an Endangered listing (representing a non-genuine change in status based on new information available since the time of the last assessment).
Dwarf Sawfish may now be restricted to tropical northern Australia in the Western Central Pacific and Eastern Indian Ocean. The species is known to occur from the Pilbara coast of northwestern Australia through the Kimberley region and the Northern Territory to at least the Gulf of Carpentaria, Queensland (Compagno and Last 1999, Last and Stevens 2009). Historically it may also have occurred on the northeastern coast of Queensland as far south as Cairns, but there are no verified records, either recent or historic, to confirm this (S. Peverell pers. comm. 2010, DSEWPaC 2011). The Kimberley and northern Pilbara represent a globally significant area for Dwarf Sawfish (Thorburn et al. 2008, Morgan et al. 2011).
There has been a long suspicion that the Dwarf Sawfish could have had a more widespread distribution in the Indo-West Pacific (Last and Stevens 1994, 2009; Compagno and Last 1999), but this has just been confirmed by the recovery of historical museum records (from the 1800s) from scattered Indo-West Pacific locations. Verifiable historic records are restricted to: Papua New Guinea (specimen held in the Nationaal Natuurhistorisch Museum – Naturalis, Leiden, collected in 1828); Calcutta, Bay of Bengal, India (The Natural History Museum, London, collected in the 1840s); and, Indonesian Borneo (Zoologisches Museum der Humboldt Universität Berlin, Germany, collected in 1894) (Faria et al. 2013). Other museum records include Réunion, non-specific locations such as the ‘West Pacific’ and the ‘Indian Ocean’, and rostra from Malaysian Borneo and Java, Indonesia (Faria et al. 2013). There are no recent records from outside of Australian waters
A possible Dwarf Sawfish (poor photographs preclude accurate identification) landed at a port on the Musandam Peninsula of eastern Arabia (possibly Khasab, Oman; photographs posted 26 January 2006) could have been caught in the easternmost Persian (Arabian) Gulf, the Gulf of Oman, or even the northwestern Arabian Sea (A. Moore pers. comm. 2012).
It is possible that the species persists outside of northern Australia, but its wider status is unknown. As currently known, Dwarf Sawfish may now have the smallest known range of any sawfish species.
Native:Australia (Northern Territory, Queensland, Western Australia)
Possibly extinct:India; Indonesia; Malaysia; Papua New Guinea; Réunion
|FAO Marine Fishing Areas:||
Indian Ocean – eastern; Indian Ocean – western; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
A lack of any confirmed records outside of Australia since the 1800s implies that the global population has undergone a significant decline and range contraction; sawfishes have been seriously depleted in places such as eastern Indonesia, Borneo and India. Despite uncertainty regarding the extent of the species’ wider historical range, it can be considered ‘possibly extinct’ outside of Australia with the disappearance of the species probably occurring outside of the last three generation period (pre-1960s; considering that there are no confirmed records since the 1800s).
All sawfish species have undergone significant, albeit largely unquantified, declines in Australia. In places, viable populations persist, representing some of the last viable populations in the Indo-West Pacific, with Australia being one of a limited number of global strongholds for sawfish (Stevens et al. 2005, DSEWPaC 2011).
The current population size and historical abundance of Dwarf Sawfish is unknown. Species-specific data to accurately ascertain the status of Australian sawfishes is generally lacking and the evidence for decline and range contraction is largely anecdotal. Data from the Queensland Shark Control Program, which operates ‘bather protection’ fishing gear along the Queensland east coast, shows a clear decline in sawfish catch (non species-specific) over a 30 year period from the 1960s and the complete disappearance of sawfish in southern Queensland (Stevens et al. 2005). All Pristis species are now extremely rare along the Australian east coast (the area in which human population pressure is greatest) where they have undergone a considerable range contraction. However, given the uncertainty about its occurrence on the Queensland east coast, whether this contraction applies to Dwarf Sawfish is questionable. This species is considered to be rare in both the Gulf of Carpentaria and the Northern Territory (Peverell 2005, Last and Stevens 2009, Phillips et al. 2011). However, recent surveys in an estuarine area of the Northern Territory that has been closed to commercial fishing for over 20 years suggest that such areas may support relatively high densities of this species (P. Kyne unpublished data).
Genetic data indicate low to moderate genetic diversity, with very low diversity in the Gulf of Carpentaria population. Populations in Western Australia, the northern coast of the Northern Territory and the Gulf of Carpentaria are distinct genetic stocks (Phillips et al. 2011, Phillips 2012).
While specific management measures are now in place in Australia, including full species protection, education of fishers about safe release practices, and fishery-specific management, threats are ongoing and there is no information to suggest that the population is recovering from previous declines. However, the extent of the decline in northern Australia is unlikely to have reached ≥80% over the last three generation lengths (~49 years). Declines of 50-80% are inferred from capture in continuing commercial fisheries, with the Dwarf Sawfish particularly susceptible given its restricted inshore occurrence and relatively limited global range.
|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).
Like other sawfishes, the toothed rostrum and demersal occurrence makes Dwarf Sawfish extremely susceptible to capture in gillnets and demersal trawl nets (Stevens et al. 2005). Datasets indicate that net fisheries account for the greatest bycatch of sawfish (all species) across northern Australia (80.2%) followed by trawling (16.6%), line fishing (9.2%) and recreational fishing (0.3%) (Stevens et al. 2005). Dwarf Sawfish are captured by all these fishing activities (Giles et al. 2004) and declines in Dwarf Sawfish are suspected based on the susceptibility of the species to these fishing activities that are ongoing across most of their currently-known, and relatively limited, distribution (Larson et al. 2006). A survey across northern Australia from Western Australia to Queensland appears to support the assertion that fishing is responsible for declines, as it found greater numbers of sawfish in areas of lower fishing pressure (both commercial and recreational) (Thorburn et al. 2003). The sustainability of Dwarf Sawfish populations in northern Australia is considered to be at high risk due to the cumulative effects of all fisheries, and the species’ low biological productivity and susceptibility to gillnets (Salini et al. 2007).
Surveys in the Queensland Gulf of Carpentaria Inshore Fin Fish Fishery (GIFFF), a multi-species gillnet fishery, reported capture rates of Dwarf Sawfish at 0.83 sawfish/net/day, with all catches occurring in the post wet season months and in the coastal zone. Dwarf Sawfish were captured in all coastal regions of the fishery but in low and variable abundance (Peverell 2005). The GIFFF operates along the entire Gulf of Carpentaria coastline and presents a high risk to the sustainability of the species (Salini et al. 2007). In 2010, five Dwarf Sawfish interactions were reported in this fishery, with new protected species interaction measures currently under development (DEEDI 2011a). The Queensland East Coast Inshore Fin Fish Fishery has not reported any interactions with this species (DEEDI 2011b), but this may be due to the uncertain occurrence of this species in this region or problems with identification. As this fishery would likely interact with them if they were present, this tends to support the suggestion that they are no longer present along the Queensland east coast if they had historically occurred there at all.
The Northern Territory (NT) commercial fishery logbook and observer data recorded 1,852 sawfish captures between 1994 and 2004, with the majority of these from the Offshore Net and Line Fishery (ONLF) (n=1,732), followed by the NT Barramundi Fishery (n=61) and the NT Restricted Bait License (n=35). None of the captures were species-specific and there is only limited observer coverage of the ONLF and barramundi fisheries (Giles et al. 2004), and very little coverage of the bait fishing licenses.
The ONLF targets blacktip sharks (Carcharhinus tilstoni, C. limbatus and C. sorrah) and Grey Mackerel (Scomberomorus semifasciatus) and operates across the NT coastline using mostly pelagic gillnets in the coastal zone with bottom set gillnets prohibited (Davies 2010). Observer data suggests that catches of Dwarf Sawfish in the ONLF are very low, which is consistent with the occurrence of this species in depths less than 20 m. All observed captured sawfish have been Narrow Sawfish (Anoxypristis cuspidata), except for one capture of a Dwarf Sawfish (Davies 2010). Preventative strategies aimed at reducing sawfish captures in this fishery were introduced in 2004 which have seen the reported catches reduced from 50 tonnes of sawfish in 2004 to less than 1 tonne in 2006 (DEWSPaC 2011).
The NT Barramundi Fishery is a relatively small, inshore, mixed species gillnet fishery operating from the Queensland border in the Gulf of Carpentaria to the Western Australia border in the west. Across this area, there are closures to netting in most of the major rivers and effort in the fishery has significantly reduced over the past 30 years (from ~100,000 hundred-metre-net-days to ~20,000 hundred-metre-net-days) (NTG 2012). However, given the large inshore coastal area of this fishery and the use of gillnets, capture rates of Dwarf Sawfish are probably not insignificant. A limited observer survey in 2007 (n=40 days of fishing, representing only 0.3% of effort in that year) reported a capture rate of 0.38 Dwarf Sawfish per day with a total of 20 Dwarf Sawfish recorded and a mortality rate of 45% (Field et al. 2008). In contrast, observer coverage since 2009 (limited to 10–40 days per year) has not recorded a Dwarf Sawfish (T. Saunders pers. comm. 2013). Dwarf Sawfish bycatch in the fishery may be spatially or temporally patchy and more consistent observer coverage would be needed to ascertain bycatch and mortality levels.
In northern Western Australia (WA), Dwarf Sawfish are captured in the inshore gillnet fishery (DWA 2011). Prior to 2005 when all sawfish were protected in WA, the Kimberley Gillnet and Barramundi Managed Fishery was estimated to have captured 12.0–16.7 tonne (live weight) of Dwarf Sawfish annually over the period 2000–2004 (McAuley et al. 2005) with the proportion of the catch that was landed unknown. Assuming an average individual weight of 12 kg (based on numbers and weights provided in Table 5.9 of McAuley et al. 2005), the above live weight equates to 1,000–1,391 individuals annually over the period 2000–2004. In 2010, the catch of sharks and rays had dropped significantly with a total of 1.3 tonne of all sharks and rays reported (DWA 2011). Dwarf Sawfish has been identified as one of the least sustainable species in this fishery (Salini et al. 2007).
The target shark fishery in northern WA uses pelagic gillnets and demersal longlines and operates offshore. It has been reported to capture Dwarf Sawfish, but the effort is limited, the fishery is almost inactive and it does not currently represent a threat to this species (Salini et al. 2007, DWA 2011).
The Northern Prawn Fishery (NPF), which operates across northern Australia, interacts with Dwarf Sawfish but possibly rarely, with only two captures reported over five years of research and commercial observer surveys (Giles et al. 2004). Commercial logbook records from 2008 reported 458 sawfish interactions, though this is considered an under-reporting of interactions and as it was for all sawfish species, the proportion that were Dwarf Sawfish is unknown (DSEWPaC 2011). In a risk assessment of the NPF, all sawfishes, including Dwarf Sawfish were amongst the least sustainable elasmobranchs, due to a combination of their susceptibility to capture and resultant mortality, and their limited ability to recover after depletion (Stobutzki et al. 2002).
The extent to which recreational fishers interact with Dwarf Sawfish across northern Australia is unknown, but there are records of recreational interactions in even relatively remote locations such as the Keep River estuary of the NT. In some areas where the species has been recorded, for example, Darwin Harbour and the South Alligator River estuary in the NT, recreational fishing is a popular activity, which is increasing in popularity and could pose a threat to the species. In the Fitzroy River (WA), recreational fishers have been reported killing incidentally caught Largetooth Sawfish (P. pristis) for the ‘trophy’ rostrum and as Dwarf Sawfish also occur in this region they may also be at risk (Thorburn et al. 2003).
Sawfish (non species-specific records) have been recorded in derelict fishing nets in northern Australian waters; the Gulf of Carpentaria is a particular hotspot for these ‘ghost nets’ (Gunn et al. 2010) and capture in these may result in sawfish mortality. Because of their toothed rostrum, sawfish may be exceptionally susceptible to entanglement in other types of marine debris, and entanglement has been reported in a number of types of marine debris (Seitz and Poulakis 2006). Entanglement in discarded or lost recreational fishing line may occur on occasion, as has been documented for other sawfish species in Australian waters (Thorburn et al. 2004), but this is considered to be a relatively minor threat to Dwarf Sawfish.
Historically, there have been foreign fishing vessels in Australia’s northern waters, though most of these operated offshore and were not likely a threat to Dwarf Sawfish. An exception may have been Soviet trawlers that operated throughout the nearshore waters of the Gulf of Carpentaria and northwestern WA. They fished between 1966 and 1978 and were reported to capture sawfish, though there is no species-specific information (Giles et al. 2004).
Across northern Australia, habitat degradation is not a major threat to Dwarf Sawfish as it occurs across relatively remote and unpopulated areas (Peverell 2005). Mining activities, through habitat alteration or potential pollution events, may however affect populations.
Outside of Australia, in the historical Indo-West Pacific distribution of Dwarf Sawfish, fishing pressure on the coastal zone is high, as is the exploitation of elasmobranchs. Unregulated and unmanaged fisheries, and habitat loss and degradation all threaten sawfishes across the region. Considerable population declines and localised extinctions have been reported for sawfish species throughout the Indo-West Pacific and if Dwarf Sawfish persist outside of Australia, the outlook for any remnant populations is not likely to be good.
Within Australia, Dwarf Sawfish has the following conservation and protected status listings: Australian Commonwealth waters, Vulnerable (Environment Protection and Biodiversity Conservation Act 1999); Queensland, Protected (Fisheries Act 1994); Northern Territory (NT), Vulnerable (Territory Parks and Wildlife Conservation Act 2000); Western Australia (WA), Totally Protected (Fish Resources Management Act 1994). The take of the species is therefore prohibited within Australian Commonwealth, state and territory waters. Dwarf Sawfish is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), prohibiting any international trade in the species (Dwarf Sawfish were collected for the aquarium trade prior to this listing and exported; DSEWPaC 2011).
In addition to the above legislated regulations, the Commonwealth, Queensland, NT and WA all have fisheries management plans in place for interactions with protected species, including Dwarf Sawfish. These include mandatory reporting of interactions with these species, release of live animals, observer coverage of most of the fisheries (although this is very low in state and territory fisheries which are likely to interact with Dwarf Sawfish) and education programmes for fishers on identification and ways to minimise interactions with this species. The Queensland Government has published a guide to the safe release of sawfish for commercial fishers (DEEDI 2010) and the NT shark fishers have a Code of Practice for the release of live sawfish from gillnets (Salini et al. 2007).
Several spatial closures in riverine, estuarine and coastal waters in the NT Barramundi Fishery, offer Dwarf Sawfish some refuge from commercial gillnet fishing activities in the NT. Similarly, spatial closures in important sawfish habitat areas of Port Musgrave and the Wenlock River in the Queensland Gulf of Carpentaria offer some protection (DEEDI 2009). Closed areas within the Great Barrier Reef Marine Park and the closure of rivers in Princess Charlotte Bay to gillnetting would afford protection to Dwarf Sawfish if they occur on the northeastern Queensland coast. Seasonal spawning closures for the take of Barramundi (Lates calcarifer) throughout much of the range (mostly during the summer wet season) add a level of protection to the species, however, information on Dwarf Sawfish long-term movement patterns and habitat use are required in order to assess the benefits of closed areas and seasons not specifically designed for sawfish.
In the prawn trawl fisheries (Northern Prawn Fishery and Queensland East Coast Trawl Fishery), the use of turtle exclusion devices (TEDs) and bycatch reduction devices (BRDs) is mandatory, though the benefit of these devices on sawfish is poorly quantified. In a Northern Prawn Fishery study, they have been shown to reduce the catch of Narrow Sawfish (Anoxypristis cuspidata), however, they and other sawfish species are still being caught as their rostra become tangled in the body of the net (Brewer et al. 2006).
Outside of Australia, awareness needs to be raised, and regulations put in place to protect all sawfishes and promote population recovery. While sawfishes (Largetooth P. pristis, Narrow and Green Sawfish P. zijsron) are theoretically protected in India (Indian Wildlife (Protection) Act), threats continue with little beneficial management, although increasing awareness of sawfishes in India is encouraging.
|Citation:||Kyne, P.M., Rigby, C. & Simpfendorfer, C. 2013. Pristis clavata. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 09 March 2014.|
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