|Scientific Name:||Pristis zijsron|
|Species Authority:||Bleeker, 1851|
|Taxonomic Notes:||Recent taxonomic work has confirmed that the Green Sawfish (Pristis zijsron) is a valid species with an Indo-West Pacific distribution (Faria et al. 2013).|
|Red List Category & Criteria:||Critically Endangered A2cd ver 3.1|
|Reviewer/s:||Böhm, M., Pillans, R. & Kyne, P.M.|
The Green Sawfish (Pristis zijsron) is probably the largest of the sawfish species, reaching lengths in excess of 7 m, although currently lengths greater than 6 m are rare. Historically, it occurred widely in the Indo-West Pacific from southern Africa to Australia and Taiwan, including the Red Sea, Persian (Arabian) Gulf and some of the Indian Ocean islands. The Green Sawfish is a coastal species, with the young occurring in shallow nearshore waters, while the adults are more common offshore in waters to >70 m. Its life history is poorly known, with data from the Gulf of Carpentaria (northern Australia) indicating that it has low intrinsic rates of population increase, making its resilience to fishing pressure low and its recovery from depletion slow. While the current population size and historic abundance is unknown, it is suspected as having declined in all of its range states. In Australian waters, its range has been well documented to have contracted significantly. Like all sawfishes, the toothed rostrum and demersal occurrence makes Green Sawfish extremely susceptible to capture in gillnets and demersal trawl nets. Historically, the population has been negatively affected by commercial net and trawl fisheries which operate in inshore areas throughout most of its range, the cumulative impacts of which have led to population declines. This species is now protected by no-take status in some range states (e.g. Australia, Bahrain, India), is listed on Appendix I of CITES, and is protected by some areas that are closed to fishing; but these actions alone will not be sufficient to ensure its survival in most regions. Despite a lack of quantitative data to support declines, available information indicates that populations of Green Sawfish are considerably rarer than historically across its entire range. Australia has some of the last remaining viable populations of Green Sawfish in the world, albeit at significantly reduced levels. Declines in the population are suspected to exceed 80% over three generation lengths (~44 yr), and it is possible that there has been localised extinction in a number of range states due to intensive fishing, reducing its extent of occurrence, and supporting its listing as Critically Endangered.
Green Sawfish have a broad Indo-West Pacific distribution, from South Africa north along the east coast of Africa, through the Red Sea, Persian (Arabian) Gulf, southern Asia, Indo-Australian archipelago, and east Asia as far north as Taiwan and southern China (Fowler 1941, Blegvad and Løppenthin 1944, Smith 1945, Misra 1969, Compagno et al. 2002a, 2002b, Last and Stevens 2009). This sawfish may be the most tolerant of cooler waters, and as such has the most pole-ward distribution of all of the sawfish, at least in the southern hemisphere. For example, in Australian waters this species historically occurred as far south as Sydney on the east coast, while the limits of other species are much farther north. The Red Sea and Persian (Arabian) Gulf are regions of presumed historic abundance (M. McDavitt pers. comm. 2012, A. Moore pers. comm. 2012, R. Jabado pers. comm. 2012), as is the northwest of Australia (Morgan et al. 2011). Its current occurrence in much of this range is uncertain due to a lack of reliable data, but it is presumed to have been extirpated from much of this area because of intensive inshore gillnet and trawl fisheries.
Native:Australia (New South Wales - Possibly Extinct, Northern Territory, Queensland, Western Australia); Bahrain; Eritrea; Indonesia; Kenya; Malaysia; Papua New Guinea; Qatar; Sudan; Timor-Leste; United Arab Emirates
Possibly extinct:Mauritius; Réunion; South Africa; Thailand
|FAO Marine Fishing Areas:||
Indian Ocean – eastern; Indian Ocean – western; Pacific – northwest; Pacific – southwest; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
Data from northern Australia shows low to moderate levels of genetic diversity, with the lowest genetic diversity in the Gulf of Carpentaria. Populations in Western Australia and the Gulf of Carpentaria are distinct genetic stocks, with the remnant east coast population potentially also forming a distinct population (Phillips et al. 2011, Phillips 2012). Genetic data is not available for the remainder of the range, but given the Australian data the global population is likely to consist of a number of stocks.
There are very limited data available on the size and trend of the Green Sawfish population, either at the global or national scale. In Australian waters, all sawfish species have undergone significant, albeit largely unquantified, declines; the southern extent of the range of Green Sawfish on the Australian east coast has contracted from Sydney, New South Wales (NSW), to the Whitsunday region of Queensland (Harry et al. 2011). The last records from NSW were in 1972 (NSWDPI 2007) and in Moreton Bay (Queensland) in the 1960s (Johnson 1999). Extensive surveys of fish landing sites throughout Indonesia since 2001 have failed to observe this species (W. White pers. comm. 2012), suggesting that its occurrence in this region is now questionable. There is some evidence from the Persian (Arabian) Gulf (A. Moore pers. comm. 2012) and Red Sea (e.g. Sudan) of small but extant populations. The lack of data from surveys and fisheries in much of the remainder of its range suggests that the abundance of this species has declined significantly in most, if not all, areas, and is now at only a small fraction of its historic abundance. A population decline of >80% is suspected across the global range over the period of the last three generations.
|Habitat and Ecology:||
Green Sawfish are most common in shallow water coastal and estuarine areas, but occur to depths to over 70 m (Stevens et al. 2005). A 3.5 m female tracked in the Gulf of Carpentaria (Australia) over a 27 hour period remained in shallow water (mean depth <1 m) and within 200 m of a mangrove shoreline (Peverell and Pillans 2004). Similarly, a 2.5 m male tracked in northwestern Australia showed similar movements, remaining in nearshore waters <1.5 m deep (Stevens et al. 2008). The young are known to use nearshore and estuarine areas as nurseries, and adults occur more broadly and into deeper areas as evidenced by the occurrence of large mature individuals in offshore trawl fisheries in northwestern Australia (Stephenson and Chidlow 2003).
Green Sawfish may be the largest of the sawfishes, with reports of individuals in excess of 7 m total length (TL). However, most reports suggest lengths over 6 m TL are currently rare. Mean size at birth in the Gulf of Carpentaria is 76 cm TL, and size at maturity at 340 to 380 cm TL (Peverell 2008, Last and Stevens 2009). Age and growth based on specimens from the Gulf of Carpentaria indicate that maturity is reached at about nine years, and maximum age may be >50 years (Peverell 2008). Little is known of reproductive biology. Reproduction is aplacental viviparous and litter size is about 12. Demographic models based on life history data from the Gulf of Carpentaria indicate that the generation time is 14.6 years, the intrinsic rate of population increase is very low (0.02 yr-1), and population doubling time is ~28 years (Moreno Iturria 2012).
Fishing is the primary threat to Green Sawfish. The large, toothed rostrum is easily entangled in fishing nets and other gear. In particular, inshore gillnet and trawl fisheries, which are common and intensive throughout much of the range of Green Sawfish, pose the greatest threat. Sawfishes are rarely targeted in these fisheries, but are regularly taken as retained bycatch because of the value of their fins, rostrum and meat. Data from specific fisheries is sparse, and rarely if ever to species level, making conclusions about the exact extent of the threats difficult to determine.
Data for northern Australia is probably the most comprehensive, and shows that gillnets were responsible for ~80% of records of sawfish captures (Stevens et al. 2005). The gillnet fisheries in northern Australia that are likely, or known, to interact with Green Sawfish include the Queensland East Coast Inshore Finfish Fishery (Harry et al. 2011), Gulf of Carpentaria Inshore Gillnet Fishery (Peverell 2005), Gulf of Carpentaria Offshore Gillnet Fishery (Peverell 2005), Northern Territory Barramundi Fishery (Field et al. 2008), Northern Territory Offshore Net and Line Fishery (Field et al. 2008), and the Kimberley Gillnet and Barramundi Fishery. Prawn trawl fisheries known, or suspected, to interact with Green Sawfish include the Northern Prawn Fishery, Queensland East Coast Trawl Fishery, and smaller prawn fisheries in Western Australia (e.g. Exmouth and Onslow) and New South Wales (NSW). The species is also known from fish trawl fisheries in northern Australia (Pilbara, Gulf of Carpentaria and Northern Territory). The take of Green Sawfish in recreational line fisheries is likely to occur at low levels, and recent education campaigns in Australia have aimed to reduce mortalities associated with these interactions. Outside of Australia the recent take of Green Sawfish in fisheries is poorly documented, partly because of its disappearance from many areas.
Ecological risk assessments of fisheries in northern Australia that interact with Green Sawfish have demonstrated that this species is one of the most at-risk elasmobranch species within the region. Its large size, low biological productivity, propensity for entanglement, and high value of products all contribute to this vulnerability (Salini et al. 2007, Tobin et al. 2010). Similar conclusions can be made for similar fisheries throughout its range. More detailed assessment of trawl data from Australia’s Northern Prawn Fishery indicated that the recent level of take was close to the sustainable limit (Zhou and Griffiths 2008), and when combined with the gillnet take in the same area, would undoubtedly be in excess of the level of sustainable take. As such, even in Australian waters, threats to this species are ongoing and populations are likely to continue to decline.
Green Sawfish are also taken in shark control programs in NSW, Queensland (Giles et al. 2004) and South Africa. The capture of Green Sawfish on all of these programs is now nonexistent (NSW and South Africa) or extremely rare (Queensland).
Other threats to Green Sawfish include habitat loss (particularly loss of intertidal areas, and coastal development), pollution, loss of genetic diversity and climate change. However, relative to fishing, these threats are unlikely to substantially affect global status.
Green Sawfish are fully protected in Australia by a variety of Federal (listed as Vulnerable, Environment Protection and Biodiversity Conservation Act 1999) and State legislation (Queensland, Protected [Fisheries Act 1994]; Northern Territory, Vulnerable [Territory Parks and Wildlife Conservation Act 2000]; Western Australia, Totally Protected [Fish Resources Management Act 1994]; New South Wales, Presumed Extinct). There are also a variety of specific fisheries regulations and reporting requirements in most Australian fisheries that interact with Green Sawfish. Sawfish are also protected in a number of range states, including India, Bahrain and Qatar. Although protected in these range states, the lack of enforcement or specific fisheries regulations, and ongoing gillnet and trawl fisheries, means that threats are ongoing.
The Green Sawfish is listed on Appendix I of the Convention on the International Trade in Endangered Species (CITES), prohibiting any international trade in the species. However, there is evidence that some Green Sawfish products (e.g., fins) remain in trade (M. McDavitt pers. comm. 2012).
The use of turtle exclusion devices (TEDs) is mandatory in some range states, though the benefit of these devices on sawfish is poorly quantified. In an Australian study they have been shown to reduce the catch of Narrow Sawfish (Anoxypristis cuspidata), however they and other sawfish species are still vulnerable to capture as their rostra become tangled in the body of the net (Brewer et al. 2006).
Marine protected areas within range states may also provide significant conservation benefit to Green Sawfish. Within Australian waters, areas closed to fishing include ~30% of the Great Barrier Reef Marine Park, and some estuaries and inshore waters of the Gulf of Carpentaria, Northern Territory and Western Australia. Temporal spawning closures for barramundi, the target species in inshore gillnet fisheries in northern Australia, also provide substantial protection (up to three months in some jurisdictions). In other range states, areas closed to fishing also occur. There are no closures specifically to address threats to Green Sawfish. The effectiveness of all areas closed to fishing throughout the range remain uncertain because of a lack of information about the movements of Green Sawfish.
Significant conservation benefits have been gained through education. In Australia, sawfish-specific handling guidelines have been developed and distributed to fishers in the form of printed material, videos and face-to-face training. This has aimed to maximise the survival of sawfish during release from fishing gear. Given the size and morphology of sawfish, releasing sawfish can be dangerous and historically they were often killed or de-sawed to make gear retrieval safer and easier. Thus development of handling guidelines (e.g., DEEDI 2010) may have significant benefit, and are also important for fisheries that operate in range states where they are fully protected (e.g., Australia). Conservation benefit may also be accrued from more general education of the public through display in public aquaria and through educational materials about sawfish such as outreach material provided to schools and other interested groups. However, to date such benefits have not been quantified. These activities increase awareness of the importance of these taxa and the conservation challenges that they face garnering public support for conservation actions.
|Citation:||Simpfendorfer, C. 2013. Pristis zijsron. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 09 March 2014.|
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