Dusky Shark Carcharhinus obscurusa

Rory McAuleyb, Vic Peddemorsc, Anthony Fowlerd and Scott Hansene

Dusky Shark

Table 1: Stock status determination for Dusky Shark


Commonwealth, South Australia, Western Australia

Commonwealth, New South Wales


Western Australian

Eastern Australian

Stock status





Catch, CPUE, direct estimates of fishing mortality


CPUE = catch per unit effort; CSF = Coral Sea Fishery (Commonwealth); ETBF = Eastern Tuna and Billfish Fishery (Commonwealth); JASDGDLF = Joint Authority Southern Demersal Gillnet and Demersal Longline Fishery (Western Australia); MSF = Marine Scalefish Fishery (South Australia); OTLF = Ocean Trap and Line Fishery (New South Wales); SESSF = Southern and Eastern Scalefish and Shark Fishery (Commonwealth); WCDGDLF = West Coast Demersal Gillnet and Demersal Longline Fishery (Western Australia); WTBF = Western Tuna and Billfish Fishery (Commonwealth)

Stock Structure

Dusky Shark occurs off the west and south coasts of Australia between latitudes 18°S and 36°S1,2, and off the east coast, where the range of the species is currently undefined. Tagging studies have demonstrated Dusky Shark movements between South Australia and Western Australia3,4, and genetic analysis suggests restricted gene flow between Dusky Shark off eastern and western Australia5. Therefore, Dusky Shark in South Australian and Western Australian waters is considered to form a single biological stock (the western Australian stock). This biological stock exhibits a high degree of ontogenetic segregation, with juveniles being most common in temperate latitudes and adults in warmer northern latitudes1,6. Because of negligible recorded catches in Victoria, Tasmania and the Northern Territory, the western Australian biological stock is believed to be separated from the east coast biological stock (the eastern Australian stock). The species is therefore thought to be represented by distinct eastern and western biological stocks in Australian waters. Status is reported at the level of these biological stocks.

Stock Status

Western Australian biological stock

The cross-jurisdictional western Australian Dusky Shark stock has components in Western Australia, South Australia and the Commonwealth. This biological stock is most abundant in waters between north-west and southern Western Australia (to 120°E longitude). Its abundance in South Australian waters is generally lower, and possibly more seasonal and sporadic2,7. 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 the biological stock is determined from the Western Australian stock assessment.

Catches of Dusky Shark in the 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 1–2-year-old fish. Collectively, these age classes accounted for 89 per cent of the observed catch during the 1990s8,9. 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 data1,10. 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 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 overfishing1.

Previous assessments therefore concluded that the declining trend observed in the standardised Dusky Shark catch-per-unit-effort 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 jurisdictions2,6,7. This evidence indicates that the biomass of the biological stock was likely to be recruitment overfished. However, for the period 2006 to 2012, an increasing trend in the effective catch-per-unit-effort data suggests improved recruitment rates and a recovering biological stock. Thus, following the comprehensive measures to mitigate cryptic mortality of older Dusky Sharks within all Western Australian–managed commercial fisheries, and to reduce catches of juveniles to less than the levels determined to be sustainable in the mid-1990s, current management arrangements are considered suitably precautionary to ensure that the biological stock continues to recover from its recruitment overfished state.

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

Eastern Australian biological stock

In New South Wales, Dusky Shark was not identified and reported at the species level in the commercial catch logbooks until 2009. Observer data indicate that whaler sharks represent the second highest shark species catch in the Ocean Trap and Line Fishery (New South Wales), at 15 per cent of the overall catch11. Insufficient information is available to determine status for any of the whaler shark species in New South Wales, including Dusky Shark 12.

Dusky Shark is taken as a nontarget species by Commonwealth fishers in the Eastern Tuna and Billfish Fishery, but its biological stock status has not been assessed. Occasional very small catches (200 kg or less) of Dusky Shark have also been reported from the Coral Sea Fishery (Commonwealth). Research is currently under way to confirm the stock status of Dusky Shark.

Insufficient information is available to confidently classify the status of this stock, and the biological stock is therefore classified as an undefined stock.

Table 2: Dusky Shark biology1,9,13

Longevity and maximum size

Females: >40 years, >2890 mm FL
Males: >32 years, 3560 mm TL (~2920 mm FL)

Maturity (50%)

Females: 27–35 years; 2540 mm FL

FL = fork length; TL = total length

Figure 1: Distribution of reported commercial catch of Dusky Shark in Australian waters, 2013 (calendar year)
Figure 1: Distribution of reported commercial catch of Dusky Shark in Australian waters, 2013 (calendar year)

Note: Catch includes undifferentiated whaler shark catch.

Table 3: Main features and statistics for Dusky Shark fisheries in Australia, 2013 (calendar year)


Western Australia

South Australia

New South Wales


Fishing methods


Demersal gillnet

Demersal longline

Pelagic longline


Hand line


Rod and line

Hand line






Management methods


Limited entry

Effort limits

Gear restrictions

Spatial closures

Possession limits

Processing restrictions

Maximum size limit


Bag limits

Gear restrictions

Size limit


Gear restrictions

Bag limits

Section 37(1)(c1), Aboriginal cultural fishing authority

Active vessels



97 in MSF


12 in OTLF

0 in CSF

21 in ETBF

0 in SESSF

0 in WTBF



137.2 t in JASDGDLF (Dusky)

8.2 t in WCDGDLF (Dusky)

57.2 t in MSF (whaler)

<1 t in NSWSMP14

2.4 t in OTLF (whaler)

0 t in CSF

2.8 t in ETBF (Dusky)

0 t in SESSF

0 t in WTBF


<10 t of whaler sharks caught from boats is retained15

Shore-based catches are undetermined

6.3 t (2007–08)16

Shore-based catches are undetermined but consist primarily of juveniles


Undetermined but likely to be negligible








CSF = Coral Sea Fishery (Commonwealth); ETBF = Eastern Tuna and Billfish Fishery; JASDGDLF = Joint Authority Southern Demersal Gillnet and Demersal Longline Fisheries (Western Australia); MSF = Marine Scalefish Fishery (South Australia); NSWSMP = NSW Shark Meshing Program; OTLF = Ocean Trap and Line Fishery (New South Wales); SESSF = Southern and Eastern Scalefish and Shark Fishery (Commonwealth); WCDGDLF = West Coast Demersal Gillnet and Demersal Longline Fisheries (Western Australia); WTBF = Western Tuna and Billfish Fishery (Commonwealth)

a 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.

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

c The Aboriginal Fishing Interim Compliance Policy 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 themselves.

d The Aboriginal cultural fishing authority is the authority that Indigenous persons can apply to to take catches outside the recreational limits under the New South Wales Fisheries Management Act 1994, section 37(1)(c1) (Aboriginal cultural fishing authority).

e Subject to the defence that applies under section 211 of the Native Title Act 1993 (Cth), and the exemption from a requirement to hold a recreational fishing licence, the non-commercial take by indigenous fishers is covered by the same arrangements as that for recreational fishing.

Figure 2: Commercial catches of whaler sharks in Australian waters, 1999 to 2013 (calendar years)

Note: Because Western Australian (state) Dusky Shark catches cannot be precisely differentiated from those of the conspecific Bronze Whaler (Carcharhinus brachyurus) before 2006, and South Australian catches are reported as undifferentiated whaler sharks, Western Australian (state) catches are for Dusky Shark and Bronze Whaler combined. Data for eastern Australian biological stock is only for Dusky Shark.

Effects of fishing on the marine environment
  • Recent analysis of potential changes in ecosystem structure of finfish in the South and West Coast Bioregions17 found no evidence of any systematic change in species diversity or richness, or trophic index, indicating that this fishery is not having a material impact on the food chain or trophic structure.

  • The demersal gillnets used to catch Dusky Shark in Western Australia are deployed infrequently, over a small proportion of the target fisheries’ operational area. Under normal circumstances, the physical impact of the gear on benthic habitats is minimal6.

  • Demersal gillnets are known to interact with a number of threatened and protected species in areas where they are used to catch Dusky Shark. However, such interactions occur at a very low frequency, and have been assessed as posing low to negligible risks to these populations6 .

Environmental effects on Dusky Shark
  • Climate change and climate variability have the potential to impact fish stocks in a range of ways, including influencing their geographic distribution (for example, latitudinal shifts in distribution). The impact of environmental changes on Dusky Shark stocks is unknown.

a Dusky Shark catches have historically been reported together with catches of similar-looking and co-occurring whaler sharks. Throughout this chapter, the term ‘Dusky Shark’ refers specifically to Carcharhinus obscurus, whereas the term ‘whaler shark’ refers to C. obscurus in combination with other whaler shark species, particularly Carcharhinus brachyurus.
b Department of Fisheries, Western Australia
c Department of Primary Industries, New South Wales
d South Australian Research and Development Institute
e Australian Bureau of Agricultural and Resource Economics and Sciences