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Spot-Tail Sharks are found in northern Australian waters, usually over shallow continental shelf and inshore waters. Genetic and tagging studies have revealed sufficient movement to ensure gene flow among Spot-Tail Sharks in Northern Australia, and reporting here is consequently at the biological stock level. The stock is sustainable. Previous editions of the SAFS reports have combined Australian Blacktip Shark, Common Blacktip Shark and Spot-Tail Shark, but all three are now reported at the species level.

Photo: CSIRO Australian National Fish Collection

Spot-tail Shark (Carcharhinus sorrah) are medium-sized Whalers that are common over open areas on the shallow continental and insular shelves in northern Australian and Indo-West Pacific waters [Last and Stevens 2009]. Spot-tail Shark form discrete populations across deep water boundaries, with the Australian population thought to be distinct [Giles et al. 2014, Naylor et al. 2012]. While stock differentiation between Australia and other regions is well established, population structure within Australia is less clear. Genetic studies have found low to no genetic structuring within Australia waters [Giles et al. 2014, Lavery and Shaklee 1989, Ovenden et al. 2007] and tag release research has shown that Spot-tail Shark display movements that would provide sufficient gene flow to prevent genetic stock differentiation [Stevens et al. 2000]. 

Here, assessment of the stock status for Spot-tail Sharks is presented at the biological stock level—Northern Australia.

Northern Australia

The Northern Australian biological stock straddles three jurisdictions: Western Australia, The Northern Territory (NT) and Queensland.

Spot-tail Sharks are relatively easily distinguished from other blacktip shark species and have been recorded to species level in NT commercial logbooks since 2000. In the Northern Territory Spot-tail Shark is primarily taken in the Offshore Net and Line Fishery (ONLF) under a species specific total allowable catch limit, which is managed through an individual transferable quota system. NT commercial catches from this stock have declined to relatively low levels since 2012, averaging 15 t a year from 2013 to 2019, compared to an average of 109 t a year over the preceding six years. This decrease in catch was largely driven by changing operational practises in the NT ONLF [Northern Territory Government 2017]. 

In Queensland, Spot-tail Sharks are harvested in the East Coast Inshore Fin Fish Fishery and the Gulf of Carpentaria Inshore Fin Fish Fishery. Since 2000, the estimated total annual commercial and recreational catch has ranged from 19–99 t on the east coast and 71–147 t in the Gulf of Carpentaria. In 2019, the estimated combined catch on the east coast was 19 t (ten year average of 56 t) and in the Gulf of Carpentaria 76 t (ten year average of 113 t). In 2009 Queensland introduced a 600 t annual total allowable commercial catch (TACC) limit (species combined), applying to all sharks and rays retained for sale on the Queensland east coast. This TACC was introduced in conjunction with an ‘S’ fishing symbol that significantly reduced the number of licences permitted to target sharks in high quantities. Recreational harvest in Queensland is limited to one shark in possession and maximum legal size of 1.5 m total length. 

An assessment was undertaken for the Northern Australian biological stock utilising a stock reduction analysis model. CPUE from the pelagic gillnet component of the ONLF was used as the abundance indicator for this assessment. The results estimate that biomass in 2019 was 91 per cent of the unfished levels and that fishing mortality in 2019 was 14 per cent of that required to reach maximum sustainable yield [Usher et al. 2020]. The results of this assessment are consistent with mark-recapture studies undertaken on all species of Blacktip Shark in Northern Territory waters [Bradshaw et al. 2013], a previous assessment undertaken for the Northern Territory and West Australian portion of this stock [Grubert et al. 2013] and an assessment that demonstrates that Spot-tail Shark are being fished within sustainable limits on the east coast of Australia [Leigh 2015].  

Although there is uncertainty regarding species composition and the magnitude of historical catches of Blacktip Sharks from Western Australia, commercial harvests of Spot-tail Shark in this jurisdiction have been negligible since April 2009 [Molony et al. 2013], allowing the biomass to increase. In addition, recreational catches are negligible [Ryan et al 2019]. 

On the basis of the evidence provided above, the Northern Australian biological stock is classified as a sustainable stock.

[Harry 2011, Last and Stevens 2009].

Northern Territory – Charter (management methods) In the Northern Territory, charter operators are regulated through the same management methods as the recreational sector but are subject to additional limits on license and passenger numbers.

Northern Territory – Indigenous (management methods) The Fisheries Act 1988 (NT), specifies that “…without derogating from any other law in force in the Territory, nothing in a provision of this Act or an instrument of a judicial or administrative character made under it limits the right of Aboriginals who have traditionally used the resources of an area of land or water in a traditional manner from continuing to use those resources in that area in that manner”.

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

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