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Dusky Whaler is a common, large-bodied whaler shark shark found throughout tropical and temperate waters of Australia.  In Western Australia stocks are recovering and there is a sustainable stock in eastern Australia.

Dusky Whaler has a tropical to warm-temperate distribution and is found off the west, south and north coasts of Australia, mostly between latitudes 18°S and 36°S [McAuley et al. 2007; Rogers et al. 2013a], and off the east coast, where the full extent of the species' geographic distribution is unclear. Electronic and conventional tagging studies have shown Dusky Whalers move between South Australia and Western Australia [Simpfendorfer et al. 1999; Rogers et al. 2013b; Huveneers et al. 2014, 2021] and between Queensland, New South Wales, Victoria and Tasmania [Huveneers et al. 2021], and genetic analyses suggest there is restricted gene flow between Dusky Whaler off eastern and western Australia [Geraghty et al. 2014]. Therefore, Dusky Whaler in South Australian, Western Australian and Northern Territory  waters are considered to form a single biological stock (the Western Australia stock). This biological stock exhibits a high degree of ontogenetic segregation, with juveniles most common in temperate latitudes and adults in warmer northern latitudes [McAuley et al. 2007, 2015].

Here, assessment of stock status is presented at the biological stock level—western Australia and eastern Australia.

Western Australia

The cross-jurisdictional Western Australia Dusky Whaler stock is taken in fisheries managed by the Commonwealth, Western Australia, Northern Territory and South Australia. This biological stock is most abundant in waters between north-west and southern Western Australia (to longitude 120°E). The whaler shark species composition in South Australia's commercial multispecies, multi-gear and multi-sectoral Marine Scalefish Fishery (MSF) is not resolved in log-books. Onboard sampling showed carcharhinid catches by the MSF largely comprised juvenile Bronze Whalers (C. brachyurus) [Rogers et al. 2013a; SARDI unpublished data]. The presence of Dusky Whalers in catches in South Australian waters is seasonally and spatially variable [Jones 2008; Rogers et al. 2013a]. 

The Commonwealth commercial catch in the Gillnet, Hook and Trap Sector (GHTS) of the Southern and Eastern Scalefish and Shark Fishery (SESSF) of Western Australia Dusky Whaler stock averaged less than one t per year during 2017–18 to 2021–22 financial years and no catch in the 2021–22 financial year. 

 Catches of Dusky Whaler in Western Australia’s Joint Authority Southern Demersal Gillnet and Demersal Longline Managed Fishery, and the West Coast Demersal Gillnet and Demersal Longline Fishery have historically consisted of neonate (young of the year) and one-to-two year-old sharks. Collectively, these age classes accounted for 89% of the observed catch during the 1990s [Simpfendorfer et al. 2002, McAuley and Simpfendorfer 2003]. The status of this stock was initially assessed using demographic modelling techniques, fishing mortality rates estimated from a tagging study in the 1990s, and contemporary catch and catch per unit effort (CPUE) data [McAuley et al. 2007; Simpfendorfer 2010]. A 2005 assessment confirmed that recorded catches of young juvenile sharks in the target fisheries have been sustainable since the mid-1990s. However, the assessment model also predicted that very low levels of fishing mortality (1–2% per year) applied to sharks older than 10 years would result in recruitment overfishing [McAuley et al. 2007]. Previous assessments therefore concluded that the declining trend observed in the effective Dusky Whaler CPUE series between the mid-1990s and 2004–05 indicated that the breeding biomass, and hence recruitment, had been gradually depleted by poorly quantified levels of intrinsic (e.g., WA Rock lobster fishery) and extraneous fishing mortality, including fisheries operating in other jurisdictions [ Jones 2008; Rogers et al. 2013a; McAuley et al. 2015; Marshall et al. 2016; Braccini et al. 2021]. Based on the above lines of evidence the stock was considered to be depleted and recruitment impaired [McAuley et al. 2015]. As a result, comprehensive measures to mitigate cryptic mortality of older Dusky Whalers within all Western Australian managed commercial fisheries, and to reduce catches of juveniles to below the levels determined to be sustainable in the mid-1990s, have been introduced since 2006–07. An increasing trend in the effective CPUE from 2006–12 was interpreted as improved recruitment and a recovering stock, suggesting that management arrangements were suitably precautionary to ensure that the biological stock continued to recover [McAuley et al. 2015].

In 2018, a stock assessment was conducted based on a risk-based weight of evidence approach using all available lines of evidence, including simulated biomass trajectories derived from a combination of demographic modelling and catch-only modelling [Braccini et al. 2018]. This assessment estimated a “Medium” current sustainability risk from fishing for the Dusky Whaler stock  [Braccini et al. 2018].

Updated stock assessments using a range of catch-only methods, state-space biomass dynamics models (JABBA, Winker et al. [2018]), integrated age-structured models (Stock Synthesis, Methot and Wetzel [2013]), and time-series of reconstructed catches, catch rates, abundance and length composition are underway (Braccini et al. unpublished). Preliminary findings, based on catch-only methods and the state space biomass dynamics model, indicate that for the last 10 years total catches have been below those required for MSY and that the recent biomass trajectory has considerably increased. In addition, fishery independent surveys of the adult component of the stock in northern western Australia show a strong increasing trend since 2016.

The above evidence indicates that the biomass of this stock is likely to be depleted and that recruitment is likely to be impaired. However, for the period 2016 to 2022 these indicators suggest a recovering stock. The above evidence indicates that the current level of fishing mortality should allow the stock to recover from its recruitment impaired state.

On the basis of the evidence provided above, the Western Australia biological stock is classified as a recovering stock.

Dusky Whaler biology [Simpfendorfer et al. 2002; McAuley et al. 2007; Geraghty et al. 2013, 2016; Kyne et al. 2021]

Distribution of reported commercial catch of Dusky Whaler

Commercial (catch) Western Australian (state) and Eastern Australia biological stock is for Dusky Whaler only. However, South Australian catches are reported as undifferentiated whaler sharks and are therefore not presented.

Commonwealth – Commercial Data provided for the Commonwealth align with 2021–22 financial year.

Commonwealth – Recreational The Australian Government does not manage recreational fishing in Commonwealth waters. Recreational fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters, under its management regulations.

Commonwealth – Indigenous The Australian Government does not manage non-commercial Indigenous fishing in Commonwealth waters, with the exception of the Torres Strait. In general, non-commercial Indigenous fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters.

Western Australia – Recreational (Management Methods) A recreational fishing from boat licence is required for recreational fishing from a powered vessel in Western Australia.

New South Wales – Indigenous (Management Methods) https://www.dpi.nsw.gov.au/fishing/aboriginal-fishing

Northern Territory - Indigenous (management methods) The Fisheries Act 1988 (NT), specifies that: “Unless expressly provided otherwise, nothing in this Act derogates or limits the right of Aboriginal people who have traditionally used the resources of an area of land or water in a traditional manner to continue to use those resources in that area in that manner.”

Queensland – Commercial QLD commercial and charter data has been sourced from the commercial fisheries logbook program.  Further information available through the Fisheries Summary Report (https://www.daf.qld.gov.au/business-priorities/fisheries/monitoring-research/data/queensland-fisheries-summary-report)  

Queensland – Indigenous (management methods) for more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing

Commercial catches of Dusky Whaler - note confidential catch not shown

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