A close-kin mark-recapture estimate of the population size and trend of east coast grey nurse shark

A close-kin mark-recapture estimate of the population size and trend of east coast grey nurse shark - was initiated to provide a contemporary population estimate of the eastern grey nurse shark (Carcharias taurus) using emerging genetic and statistical techniques. It follows on from the successful National Assessment of the Status of White Sharks (A3) project and uses a modification of the population-dynamics model used to derive a population estimate for white sharks. Importantly, due to the absence of age estimates as well as the unreliable length estimates of the sampled grey nurse shark (GNS), the GNS model had to be more elaborate to account for greater kinship possibilities.

The grey nurse shark, Carcharias taurus (GNS), is distributed primarily within the continental shelf zones of tropical and temperate regions of the North and South Atlantic, Indian and western Pacific oceans (Last & Stevens, 2009) to depths of at least 230 m (Otway and Ellis 2011). In Australia, two distinct subpopulations are recognised, one along the eastern seaboard of Australia, the other along the western seaboard. Within Australia the distribution of the eastern population extends approximately 2,700 km from central Queensland south to at least the New South Wales (NSW)/Victorian border (Otway et al. 2003; Bansemer 2009; Otway and Ellis 2011). The western population extends across a similar distance of the West Australian coastline from the North West Shelf south to at least Cocklebiddy in the Great Australian Bight (McAuley et al. 2002; Cavanagh et al. 2003; Chidlow et al. 2005). This project was focussed on deriving an abundance estimate of the eastern Australian GNS population.
The species is listed as “vulnerable” on the IUCN Red List of Threatened Species (Pollard & Smith 2009) as a result of observed declines in GNS numbers worldwide. The eastern Australian population has been declared “critically endangered” under the Australian Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and as such is the subject of an on-going recovery plan. This publication addresses Objective 1 of the 2014 recovery plan: Develop and apply quantitative monitoring of the population status (distribution and abundance) and potential recovery of the grey nurse shark in Australian waters (Australian Government Department of the Environment 2014).



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