Dusky Whaler (2020)
Date Published: June 2021
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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.
Stock Status Overview
|New South Wales||Eastern Australia||Sustainable||Catch|
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.
Dusky Whaler is taken as a non-target species by Commonwealth fishers in the Eastern Tuna and Billfish Fishery (ETBF). The species has been considered using ecological risk assessment methods and found to be at medium risk [AFMA 2018]. Catches in the ETBF have averaged around 1.8 tonnes (t) over the last 10 years. There was a small amount of catch (around 250kg) reported in the Coral Sea Fishery in 2011.
In Queensland, species-specific reporting of Dusky Whaler only commenced in 2009 and only for a sub-component of the Queensland East Coast Inshore Net Fishery. The reported harvest since this time has averaged about 2 t per year.
In New South Wales, Dusky Whaler was not identified and reported at the species level in commercial catch logbooks until 2009. Observer data indicate that whaler sharks represent the second highest shark species catch in the New South Wales Ocean Trap and Line Fishery (15 per cent of overall catch) [Macbeth at al. 2009]. Historical catch of Dusky Whaler is therefore likely to have been around 7.5 t from 2000 to 2005, whereafter increased targeting of large whaler sharks led to three years of higher catch, peaking at approximately 30 t in 2006–07. Dusky Shark catch reduced to ~15 t in 2007–08 once fishers started differentiating some of the whaler sharks in preparation of the new species-specific logbook requirements, specific conditions and restrictions being implemented in the OTL fishery [Macbeth et al. 2009]. Since 2015, under 3 t of Dusky Whaler was landed each year by the OTL fishery in New South Wales. An annual catch of less than 1 t was reported by the New South Wales Shark Meshing Program.
Application of a new software package known as NeOGen [Blower et al 2019] enabled estimation of the total population of Dusky Sharks on the eastern Australian coastline to be approximately 35 000 individuals [Blower 2020]. Simulations at current fishing levels indicate observed fishery harvest volumes to be sustainable [Blower 2020].
The above evidence indicates that the biomass of this stock is unlikely to be depleted and recruitment is unlikely to be impaired. The above evidence also indicates that the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired.
On the basis of the evidence provided above, the Eastern Australia biological stock is classified as a sustainable stock.
Dusky Shark biology [Geraghty et al. 2013, 2016 McAuley et al. 2007, Simpfendorfer et al. 2002]
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
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 (Western Australia)
Females 15.5 years, 2811 mm TL (Eastern Australia)
Distribution of reported commercial catch of Dusky Shark
|New South Wales|
|Hook and Line|
|Method||New South Wales|
|Customary fishing management arrangements|
|New South Wales|
|Recreational||Shore-based catches are undetermined but consist primarily of juveniles|
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) https://www.dpi.nsw.gov.au/fishing/aboriginal-fishing
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.
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- Blower, D. C. 2020. Estimating contemporary abundance, demography, and vulnerability to change for long-lived species with effective population size and population simulation. PhD thesis. School of Biological Sciences, p. 257. The University of Queensland.
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- 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.
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- The National Recreational and Indigenous Fishing Survey. FRDC Project No. 99/158. New South Wales Fisheries.