Dusky Whaler (2018)
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Dusky Whaler is a shark found off the western, southern and northern coasts of Australia. In WA stocks are recovering and there is an undefined stock in eastern Australia.
Stock Status Overview
|South Australia||Western Australia||MSF||Recovering||Catch, CPUE, direct estimates of fishing mortality, demographic analysis, risk assessment|
- Marine Scalefish Fishery (SA)
Dusky Shark has a tropical to warm-temperate distribution and is found off the west, south and north coasts of Australia, mostly between latitude 18°S and 36°S [McAuley et al. 2007, Rogers et al. 2013a], and off the east coast, where the range of the species is currently undefined. Electronic and conventional tagging studies have shown Dusky Sharks move between South Australia and Western Australia [Huveneers et al. 2014, Rogers et al. 2013b, Simpfendorfer et al. 1999], and genetic analyses suggest there is restricted gene flow between Dusky Shark off eastern and western Australia [Geraghty et al. 2014]. Therefore, Dusky Shark in South Australian and Western Australian 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, McAuley et al. 2015].
Here, assessment of stock status is presented at the biological stock level—Western Australia and Eastern Australia.
The cross-jurisdictional Western Australia Dusky Shark stock has components in waters of the Commonwealth, Western Australia and South Australia. This biological stock is most abundant in waters between north-west and southern Western Australia (to longitude 120°E). The carcharhinid species composition in the South Australian State-managed commercial Marine Scalefish Fishery (MSF) is not resolved in log-books. Onboard sampling showed carcharhind catches by the MSF largely comprised juvenile Bronze Whalers (C. brachyurus), with juvenile Dusky Sharks (900–3 000 mm total length) representing < 10 per cent of landings [Rogers et al. 2013a, SARDI unpublished data]. Hence, no catch data are provided in this assessment year. Presence of Dusky Shark in catches in South Australian waters is seasonally and spatially variable [Jones 2008, Rogers et al. 2013a]. Given that this stock’s primary distribution is off the south-west coast and that Western Australian catches have historically been several times higher than those in the other jurisdictions, the status of this biological stock is largely determined from the Western Australia stock assessment.
Catches of Dusky Shark 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–two year old sharks. Collectively, these age classes accounted for 89 per cent of the observed catch during the 1990s [McAuley and Simpfendorfer 2003, Simpfendorfer et al. 2002]. The status of this stock has been assessed using demographic modelling techniques, fishing mortality rates estimated from a tagging study in the 1990s, and contemporary catch and catch per unit effort () data [McAuley et al. 2007, Simpfendorfer 2010]. The most recent assessment in 2005 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 cent 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 Shark CPUE series between the mid-1990s and 2004–05 indicated that breeding biomass had been gradually depleted by low, but poorly quantified, levels of extraneous fishing mortality, including fisheries operating in other jurisdictions [Marshall et al. 2016, McAuley et al. 2015, Jones 2008, Rogers et al. 2013a]. The above evidence indicates that this stock was likely to be depleted and recruitment impaired. As a result, comprehensive measures to mitigate cryptic mortality of older Dusky Sharks 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, suggests improved recruitment rates and a recovering stock [McAuley et al. 2015], indicating that current management arrangements are suitably precautionary to ensure that the biological stock continues to recover [McAuley et al. 2015].
Recently, 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 stock reduction analysis [Braccini et al. in prep.]. This assessment estimated a “Medium” current risk level for the Dusky Shark stock, with 46 per cent, 73 per cent and 100 per cent of the simulated current (2015–16) relative total biomass trajectories being above the target, threshold and limit biomass reference points, respectively [Braccini et al. in prep.].
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 Shark biology [Geraghty et al. 2013, McAuley et al. 2007, Simpfendorfer et al. 2002]
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
|Dusky Whaler||Females > 40 years, 2 890 mm FL Males > 32 years, 3 560 mm TL (~2 920 mm FL)||Females 27–35 years, 2 540 mm FL|
Distribution of reported commercial catch of Dusky Shark
|Hook and Line|
|0, 103 in MSF|
- Marine Scalefish Fishery (SA)
|Recreational||Undetermined but likely to be negligible|
Commercial (catch) Western Australian (state) and Eastern Australia biological stock is for Dusky Shark only. However, South Australian catches are reported as undifferentiated whaler sharks and are therefore not presented.
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 commercial fisheries with less than seven active fishers are not presented due to the Privacy Act.
New South Wales – Commercial (catch) For the Ocean Trap and Line Fishery (New South Wales), only one business reported sufficient catch to suggest targeting.
New South Wales – Indigenous (Management Methods) (a) Aboriginal Cultural Fishing Interim Access Arrangement—allows an Indigenous fisher in New South Wales to take in excess of a recreational bag limit in certain circumstances; for example, if they are doing so to provide fish to other community members who cannot harvest for themselves; (b) The Aboriginal cultural fishing authority is the authority that Indigenous persons can apply to take catches outside the recreational limits under the Fisheries Management Act 1994 (NSW), Section 37 (1d)(3)(9), Aboriginal cultural fishing authority; and (c) In cases where the Native Title Act 1993 (Cth) applies fishing activity can be undertaken by the person holding native title in line with S.211 of that Act, which provides for fishing activities for the purpose of satisfying their personal, domestic or non-commercial communal needs. In managing the resource where native title has been formally recognised, the native title holders are engaged with to ensure their native title rights are respected and inform management of the State's fisheries resources.
Commercial catches of Dusky Shark - note confidential catch not shown
- Australian Fisheries Management Authority, Tropical Tuna and Billfish Management Advisory Committee (TTMAC19), Meeting Minutes, Australian Fisheries Management Authority, Canberra.
- Braccini, M, Hesp, A, Molony, B and Blay, N in prep Resource Assessment Report Whiskery, Gummy, Dusky and Sandbar Shark Resource of Western Australia. Department of Primary Industries and Regional Development.
- Geraghty PT, Macbeth, WG, Harry, AV, Bell, JE, Yerman, MN and Williamson, JE 2013, Age and growth parameters for three heavily exploited shark species off temperate eastern Australia, ICES Journal of Marine Science, 71: 559–573.
- Geraghty, PT, Williamson, JE, Macbeth, WG, Blower, DC, Morgan, JAT, Johnson, G, Ovenden, JR and Gillings, MR 2014, Genetic structure and diversity of two highly vulnerable carcharhinids in Australian waters, Endangered Species Research, 24: 45–60.
- Huveneers, C, Rogers, P and Drew, M 2014, Monitoring shark species of conservation concern within the Adelaide metropolitan and Gulf St Vincent regions, final report to the Adelaide and Mount Lofty Ranges Natural Resources Management Board, South Australian Research and Development Institute (Aquatic Sciences), SARDI publication F2013/000716-1, SARDI research report series 754, SARDI, Adelaide, 89.
- Jones, K 2008, Review of the fishery status for whaler sharks (Carcharhinus spp.) in South Australian and adjacent waters, report to the Fisheries Research and Development Corporation, FRDC project 2004/067, South Australian Research and Development Institute (Aquatic Sciences) publication F2007/000721-1, SARDI research report series 154, SARDI, Adelaide.
- Macbeth, WG, Geraghty, PT, Peddemors, VM and Gray, CA 2009, Observer-based study of targeted commercial fishing for large shark species in waters off northern New South Wales, Cronulla Fisheries Research Centre of Excellence, New South Wales Industry and Investment, Cronulla.
- Marshall, L, Giles, J and Johnson, GJ 2016, Catch composition of a traditional Indonesian shark fishery operating in the MOU Box, northwestern Australia: Results of shark fin identification from Operation Snapshot (May 2015), 2016/001375, Australian Fisheries Management Authority, Canberra.
- McAuley, R and Simpfendorfer, C 2003, Catch composition of the Western Australian Temperate Demersal Gillnet and Demersal Longline fisheries, 1994–1999, Fisheries research report 146, Western Australian Department of Fisheries, Perth.
- McAuley, R, Braccini, M, Newman, SJ and O’Malley, J 2015, Temperate Demersal Gillnet and Demersal Longline Fisheries Status Report, in WJ Fletcher and K Santoro (eds), Status Reports of the Fisheries and Aquatic Resources of Western Australia 2014/15, Western Australian Department of Fisheries, Perth, 261–272.
- McAuley, RB, Simpfendorfer, CA and Hall, NG 2007, A method for evaluating the impacts of fishing mortality and stochastic influences on the demography of two long-lived shark stocks, ICES Journal of Marine Science, 64: 1710–1722.
- Rogers, P, Huveneers, C, Goldsworthy, SD, Mitchell, JG and Seuront, L 2013, Broad-scale movements and pelagic habitat of the Dusky Shark Carcharhinus obscurus off Southern Australia determined using pop-up satellite archival tags, Fisheries and Oceanography, 22: 102–112.
- Rogers, PR, Huveneers, C, Goldsworthy SD, Cheung, WWL, Jones KG, Mitchell, JG and Seuront, L 2013, Population metrics and movement of two sympatric carcharhinids: a comparison of the vulnerability of pelagic sharks of the southern Australian gulfs and shelves, Marine and Freshwater Research, 64: 20–30.
- Rowling, K, Hegarty, A-M and Ives, M 2010, Status of fisheries resources in NSW 2008/09, New South Wales Industry and Investment, Cronulla.
- Ryan K, Hall N, Lai E, Smallwood C, Taylor S, Wise B. 2017. Statewide survey of boat-based recreational fishing in Western Australia 2015/16. Fisheries Research Report No. 287, Department of Primary Industries and Regional Development, Western Australia.
- Simpfendorfer CA, McAuley R, Chidlow JA, Lenanton R, Hall N and Bastow T 1999. Biology and stock assessment of Western Australia’s commercially important shark species. Project 96/130 Fisheries Research and Development Corporation, Department of Fisheries of Western Australia, Perth.
- Simpfendorfer, C 1999, Demographic analysis of the dusky shark fishery in southwestern Australia, in JA Musick (ed.), Life in the slow lane: Ecology and conservation of long-lived marine animals, American Fisheries Society Symposium 23, Bethesda, Maryland, 149–160.
- Simpfendorfer, CA, McAuley, R, Chidlow, J and Unsworth, P 2002, Validated age and growth of the Dusky Shark, Carcharhinus obscurus, from Western Australian waters, Marine and Freshwater Research, 53: 567–573.