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Table 1: Known key aggregation sites critical to the survival of the grey nurse shark in Australian waters 11
Table 2: Current conservation listings for the grey nurse shark in Australia 16
Table 3: List of known sightings of grey nurse sharks along the east coast of Australia, including aggregation sites that are regularly and consistently used (five or more sharks), sites where small aggregations have been observed (less than five sharks) and also sites where single sharks have been recorded on single occasions. Source: NSW DPI, unpublished data, (2002). 31
AFMA Australian Fisheries Management Authority, Commonwealth
ASFP Australian Society for Fish Biology
CSIRO Commonwealth Scientific and Industrial Research Organisation
DoE Department of the Environment
EPBC Act Environment Protection and Biodiversity Conservation Act 1999
NSW DPI New South Wales Department of Primary Industries
QDPI&F Queensland Department of Primary Industries and Fisheries
SEACAMS Sustainable Expansion of the Applied Coastal and Marine Sectors
The grey nurse shark (Carcharias taurus) is listed as two separate populations under the Environment Protection and Biodiversity Conservation Act 1999. The east coast population is listed as critically endangered and the west coast population is listed as vulnerable. A recovery plan for the species was finalised in 2002.
A review of the 2002 Recovery Plan for the Grey Nurse Shark (Carcharias taurus) in Australia was completed in 2009. The review concluded that while progress had been made on most of the recovery plan actions, there was not sufficient evidence to indicate that the population had recovered sufficiently to be removed from the list of protected species. The review further concluded that a new recovery plan was required to remove completed actions and include new conservation priorities. The Department of the Environment, with the support of key stakeholders, has developed a new recovery plan for the grey nurse shark.
This issues paper has been developed to support the development of the new recovery plan and includes information on the biology and ecology of grey nurse sharks, the species’ current conservation status, a description of the key threats endangering the species’ survival in Australian waters and recommendations for future research. Some of the key findings of this paper are:
• Recent research has obtained a relatively robust population estimate for the east coast grey nurse shark population. Recent studies suggest estimates of population size are above 1131 individuals, with the highest estimate being 2142 individuals. While this number is still very low and does not warrant changing the protected status of the east coast population from critically endangered, it is higher than previous estimates.
• Since the introduction of the 2002 Recovery Plan for the Grey Nurse Shark (Carcharias taurus) in Australia, all but one of the 19 key aggregation sites identified as habitat critical to the survival of the species in the 2002 recovery plan have been given some level of protection. The remaining site—China Wall off Moreton Island in Queensland—was ultimately not considered a key aggregation site as the sharks were not consistently seen there.
• Fishing pressure from the recreational and commercial sectors represents the greatest ongoing threat to the grey nurse shark in Australian waters, followed by mortalities as a result of the New South Wales and Queensland bather protection programs (beach meshing/drumlining1).
• Despite significant advances over the last decade in the knowledge base concerning the grey nurse shark in Australian waters, continuation of research into their ecology and biology, as well as into causes of anthropogenic mortality, will assist in developing programs to aid the long term recovery of this species.
The Recovery Plan for the Grey Nurse Shark (Carcharias taurus) 2014 can be found at: http://www.environment.gov.au/resource/recovery-plan-grey-nurse-shark-carcharias-taurus
The purpose of this paper is to provide a summary of the biology, population ecology and current threats to the grey nurse shark in Australian waters and to make recommendations on the future research necessary to protect this species. This paper has been written to inform the development of a revised recovery plan for the grey nurse shark and is designed to be read in conjunction with the Review of the 2002 Recovery Plan for the Grey Nurse Shark (Carchariastaurus) in Australia (DEWHA, 2009) and the Recovery Plan for the Grey Nurse Shark (Carcharias taurus) 2014 (DoE, 2014).
The specific objectives of this paper are to:
• collate the most recent scientific information (published and, where appropriate, unpublished) on distribution, abundance and population trends for the grey nurse shark
• identify gaps in our knowledge of the biology and threats to the species and make recommendations on future research
• discuss any natural and anthropogenic factors that are currently limiting the recovery of the species in Australian waters.
This document provides a contemporary picture of the biology and ecology of the grey nurse shark and identifies threats to its long term persistence in the wild. This document is not a recovery plan and does not prescribe management actions necessary to address population declines.
2.4 Sources of information
This document has been prepared following a review of the literature and consultation with key stakeholders including relevant government agencies, researchers and interested organisations.
2.5 Recovery planning process
2.5.1 Purpose of recovery plans
The Australian Government minister responsible for the environment may make or adopt recovery plans for threatened fauna, threatened flora (other than conservation dependent species) and threatened ecological communities listed under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).
Recovery plans set out the research and management actions necessary to stop the decline of, and support the recovery of, listed threatened species or threatened ecological communities. The aim of a recovery plan is to maximise the long term survival in the wild of a threatened species or ecological community.
2.5.2 Objectives of the Grey Nurse Shark Recovery Plan
The overarching objective of the Recovery Plan for the Grey Nurse Shark (Carcharias taurus) 2014 is to assist the recovery of the grey nurse shark in the wild, throughout its range in Australian waters, with a view to:
• improving the population status leading to the removal of the grey nurse shark from the threatened species list of the EPBC Act
• ensuring that anthropogenic activities do not hinder the recovery of the grey nurse shark in the near future, or impact on the long term conservation status of the species.
The east coast population of grey nurse shark is considered to be critically endangered and this population will be the primary focus of the actions outlined in the recovery plan, with an emphasis placed on monitoring and compliance. Although the proposed actions are still relevant to the west coast population, further information is required to better understand the status of the population in the west and the importance of critical habitat sites for that population.
3 Biology and ecology
3.1 Species description
The grey nurse shark (Carcharias taurus) (Rafinesque, 1810) is one of three species belonging to the family Odontaspididae (Last & Stevens, 2009). It is also known as the sand tiger shark in the north-west and south-west Atlantic and the spotted ragged-tooth shark in South Africa (Pollard, et al., 1996; Last & Stevens, 2009). The species has a large stout body and is coloured grey to grey-brown dorsally, with a paler off-white underbelly.
Key morphological characteristics include a conical snout, long awl-like teeth in both jaws, similarly-sized first and second dorsal fins and an asymmetrical caudal (tail) fin (Pollard, et al., 1996; Last & Stevens, 2009). The species is a slow but strong swimmer and is thought to be more active at night (Pollard, et al., 1996). The caudal fin and posterior half of the body often have reddish or brownish spots (Pollard, et al., 1996; Bansemer & Bennett, 2008; Last & Stevens, 2009). Grey nurse sharks can grow to a maximum total length of 318 cm and a maximum weight of approximately 190 kilograms (kg) (Pepperell, 1992; Cavanagh, et al., 2003; Last & Stevens, 2009).
3.2 Life history
The grey nurse shark has a relatively slow development and low reproductive rate with a long gestation period (Bass, et al., 1975; Gilmore, et al., 1983). It has an unusual reproductive mode (NSW DPI, 2002; Gilmore, et al., 2005) which includes intra-uterine cannibalism (adelphophagy), whereby embryos (about 100 mm long and with well developed teeth) hunt and consume other embryos until only one remains in each of the two uteri, resulting in only two pups in a litter (Gilmore, et al., 2005; Last & Stevens, 2009). After the cannibalistic stage (approximately 100 days after first insemination and at approximately 335 mm in length) the single remaining embryo in each uterus then feeds on unfertilised ova (oophagy) resulting in its body wall extending to produce a “yolk-gut” (Bass, et al., 1975; Compagno, 1984; Gilmore, et al., 2005). During the last 100 days no feeding on ova occurs. Instead the yolk in the gut is absorbed and the baby shark gradually resumes its normal shape in readiness for birth. Gestation is thought to take between nine and 12 months and at birth, pups are about one metre long (Last & Stevens, 2009).
Grey nurse shark reproduction has been found to be biennial—that is, these sharks pup every second year (Bass, et al., 1975; Lucifora, et al., 2002; Dicken, et al., 2006, 2007). Although grey nurse sharks are thought to have a biennial reproductive pattern in Australia, a recent study along the east coast suggests that some individuals may take an extra year between mating and/or pregnancy events potentially resulting in a three year interval (Bansemer & Bennett, 2009). However, this study was based on photo-identification and observational data alone and further work is required to verify this finding.
3.2.2 Age and growth
Studies of the grey nurse shark in South Africa and Australia indicate that individuals may live for up to 35 years in captivity (Smith, et al., 1998). There is less certainty about maximum ages reached in the wild but it is thought that wild male sharks may live for up to 30 years and female sharks for 40 years (Goldman, et al., 2006).
Research in the north-western Atlantic Ocean by Goldman, et al., (2006) indicates that growth rates of the sexes are similar up to the age of five years, at which time females outgrow males at a significant rate. The total length at maturity for females was estimated at 2.2–2.6 m (9–10 years) and for males at 1.9–2.2 m (6–7 years) (Bass, et al., 1975; Gilmore, et al., 1983; Branstetter & Musick, 1994; Lucifora, et al., 2002; Goldman, et al., 2006). Based on analysis of the Australian population, 50 per cent of males are reproductively mature at a total length of 2.1 m and 50 per cent of females are reproductively mature at a total length of 2.6 m (Otway, et al., 2009; Otway & Ellis, 2011).
The diet of adult grey nurse sharks consists of a wide range of fish, other sharks and rays, squid, crabs and lobsters (Compagno, 1984). In the north-west Atlantic the grey nurse shark diet has been shown to consist primarily of fish and elasmobranchs (dominated by rajid skates). In South Africa, grey nurse sharks have been shown to feed on herring (family Clupeidae), mackerel (family Scombridae), butterfish (family Sciaenidae), snapper (family Lutjanidae), wrasse (family Labridae), mullet (family Mugilidae), sole (family Solidae), small sharks and rays (including eagle rays and juvenile Carcharhinus spp.), squid, and occasionally crustaceans (Bass, et al., 1975; Compagno, 1984).
Over the past decade, necropsies of accidentally caught and killed grey nurse sharks from eastern Australian waters have confirmed a wide-ranging fish based diet, similar to that of grey nurse sharks in other parts of the world. The gut contents of these animals have included pilchards (family Clupeidae), mulloway (family Sciaenidae), tailor (family Pomatomidae), Australian bonito (family Scombridae), blue groper (family Labridae), snapper (family Sparidae), sea mullet (family Mugilidae), flathead (family Platycephalidae), silver trevally (family Carangidae), eastern Australian salmon (family Arripidae), small and juvenile sharks (Carcharhinus spp.) and squid (Otway, et al., 2003).
Stomach contents of 22 grey nurse sharks caught off the west coast of Australia included whiting (family Sillaginidae), buffalo bream (family Kyphosidae), breaksea cod (family Serranidae), dusky morwong (family Cheilodactylidae), mackerel (family Scombridae), pilchards (family Clupeidae), goatfish (family Mullidae), scorpionfish (family Scorpaenidae), pink snapper (family Sparidae), trevally (family Carangidae) and numerous unidentified teleosts and octopi. As all sharks examined were captured in demersal gillnets, it cannot be determined whether these dietary items represent natural prey species, or were opportunistically consumed from the same nets (McAuley, 2009). However, given the similarities with the diet of the east coast population, it appears likely these data reflect the natural diet of the Australian west coast population.
Grey nurse sharks have been recorded from tropical and temperate parts of the north and south Atlantic, Indian and western Pacific Oceans. They are known to occur on the continental shelf from the surf zone down to at least 190 m (Last & Stevens, 2009) and occasionally off the continental shelf to depths of approximately 230 m (Otway, et al., 2009). The Australian east coast population covers a range of approximately 2700 km and extends from the Capricornia Coast (central Queensland) to Narooma in southern New South Wales (Otway, et al., 2003; Bansemer, 2009; Otway, et al., 2009). Grey nurse sharks have been recorded at 153 locations along the east Australian coast as far south as the NSW/Victorian border (NSW DPI, 2002). Figure 1 includes grey nurse shark sightings collected by the New South Wales Department of Primary Industries (NSW DPI) and includes recognised aggregation sites (five or more sharks), sites where small aggregations have been observed (fewer than five sharks) and also sites where single sharks have been recorded.
The range of the west coast population is less well known. However, commercial fishery shark bycatch data, fishery and research records, as well as detailed interviews with commercial fishers, professional dive operators and members of dive clubs, indicate that the species occupies sites from the North West Shelf (including coastal waters in Exmouth Gulf), south to coastal waters near Cocklebiddy in the Great Australian Bight (McAuley, et al., 2002; Cavanagh, et al., 2003; Chidlow, et al., 2005), covering a range of approximately 2900 km.
The only Northern Territory record is from around Lynedoch Bank in the Arafura Sea (Northern Territory Department of Natural Resources, Environment and the Arts, 2006). However, as this is a single sighting it has been assumed that these sharks were either misidentified or were vagrants.