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Australian Blacktip Sharks are found along Australia’s northern coastline. The North Western Australia biological stock and the East Coast management unit are sustainable stocks, while the Gulf of Carpentaria management unit is undefined.

Photo credit: Department of Industry, Tourism and Trade, Northern Territory.

Australian Blacktip Shark (Carcharhinus tilstoni) are distributed within the waters of Northern Australia. Genetic studies have identified two biological stocks of Australian Blacktip Shark. A western stock extending from the western Northern Territory into northern Western Australia, and an eastern stock extending from the Gulf of Carpentaria to the east coast of Queensland and New South Wales [Ovenden et al. 2007]. The stock boundary between the North Western Australia and the North Eastern Australia biological stocks is uncertain. Geographic separation caused by Torres Strait most likely results in limited movement between the Queensland east coast and the Queensland side of the Gulf of Carpentaria, consequently, this species has been assessed as two management units in this state.

Australian Blacktip Shark are similar in appearance to Common Blacktip Shark (C. limbatus). Previously, taxonomic differentiation of these species was only possible by genetic analyses, precaudal vertebral counts or, in certain size classes, differences in size at maturity [Harry et al. 2011]. A new identification technique, utilising body measurements and pelvic fin colouration, has been developed and may assist in distinguishing between these two species [Johnson et al. 2017]. However, accurate field identification remains difficult and is not practical during fishing operations [Johnson et al. 2017]. Hybridisation between the species has also been recorded and while a new investigation is helping to understand the prevalence and dynamics of this phenomenon [Queensland Department of Agriculture and Fisheries, 2021], current knowledge regarding its implications for fisheries assessment and management is limited [Harry et al. 2012; Johnson 2017; Morgan et al. 2011]. Consequently, Australian Blacktip Shark and Common Blacktip Shark are often reported as a species complex in commercial logbooks. For the purpose of these assessments a portion of the combined blacktip shark catch for each jurisdiction has been attributed to Australian Blacktip Shark using relative abundance ratios determined from onboard observer programs and published research [Johnson 2017, Ovenden 2007]. 

Here, assessment of stock status for Australian Blacktip Shark is presented at the biological stock level—North Western Australia—and the management unit level—Gulf of Carpentaria (Northern Territory and Queensland) and East Coast (Queensland and New South Wales).

East Coast Queensland

The East Coast management unit straddles two jurisdictions: Queensland, east of Cape York, and northern New South Wales.  

The last Queensland stock assessment for the Australian Blacktip Shark was completed in 2015 and was based on data up to and including 2013 [Leigh 2015]. This report produced Maximum Sustainable Yield (MSY) estimates for Australian Blacktip Sharks on the Queensland east coast ranging from 144 to 670 tonnes (t). The lower bound of the MSY estimate range is highly conservative and was included in the assessment in response to concerns surrounding the quantity and quality of the available data on shark harvests [Leigh 2015]. In recent years, the annual harvest of Australian Blacktip Shark has remained below the lower extent of the MSY estimates [Leigh 2015]. In 2021–22 the annual commercial harvest was 8 t, below the 10-year average of 49 t (range = 8 t to 106 t). 

Observed declines in the annual harvest of shark are attributed to poor market demand for shark products, declining effort and management reforms targeted at the commercial net fishery as opposed to declining biomass. The most significant reforms were implemented in 2009 and included the introduction of a combined 600 t Total Allowable Commercial Catch (TACC) limit for retained sharks and rays. In 2021, this limit was reduced to 400 t (not including Hammerhead Sharks) as part of a broader reform program for the East Coast Inshore Fishery (ECIF); the primary source of regional shark product. These reforms included a transition of the ECIF to regional management and establishing a fishery-specific harvest strategy. This harvest strategy, includes reference points, trigger limits and other measures to guide the long-term management of sharks harvested on the Queensland east coast [Queensland Department of Agriculture and Fisheries, 2020]. One of the primary objectives of these changes is to minimise the long-term overexploitation risk.

Historic catch data for Blacktip Sharks have several limitations, particularly with respect to species identifications and the quantity and reliability of available catch data. Species differentiation for the Blacktip Shark complex has improved with the introduction of a new Shark and Ray logbook on 1 January 2018 that limits the ‘Blacktip Whaler’ category to C. limbatus and C. tilstoni only. As part of this process, new requirements were introduced that require operators to report shark discards. These changes were supported by monitoring programs that examined the composition, biology and genetic diversity of the shark catch [Queensland Department of Agriculture and Fisheries 2021]. These changes will assist in terms of quantifying harvest rates for Australian Blacktip Shark on the Queensland east coast.

Outside of the commercial fishing sector, the catch of Australian Blacktip Sharks is low to negligible. The Queensland Shark Control Program typically reports the capture of less than five individuals per year [Queensland Government, 2023]. No recreational data is available for this species [Teixeira et al. 2021]. However, recreational harvest is limited by a one shark in possession limit and a maximum legal size limit of 1.5 m total length.

In New South Wales, Australian Blacktip Shark are not differentiated in commercial logbooks; however, observations on commercial fishing vessels indicate that the amount of Australian Blacktip Shark caught is likely less than 0.1% of total shark catch [Macbeth et al, 2009] and therefore represents a negligible proportion of catch for this biological stock. Although Australian Blacktip Shark have been reported in the NSW Shark Meshing Program off Sydney [Boomer et al. 2010], the low number of 'Blacktip Whaler' sharks caught in the SMP [Dalton et al., 2023] imply this is a negligible proportion of overall catch for this species.  

Overall the information provided by both jurisdictions indicates that the East Coast management unit is not considered to be depleted and that recruitment is unlikely to be impaired. Furthermore, the level of fishing mortality is also unlikely to cause the management unit to become recruitment impaired.

On the basis of the evidence provided above, Australian Blacktip Shark in the East Coast management unit is classified as a sustainable stock.

[Harry, 2011; Harry et al. 2012; Last and Stevens 2009]

Distribution of reported commercial catch of Australian Blacktip Shark

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

Queensland – Commercial (Catch). Queensland commercial and charter data have been sourced from the commercial fisheries logbook program. Due to low confidence in species-specific reporting caused by challenges in distinguishing between C. limbatus and C. tilstoni, catch for this species has been derived by combining harvest across the multiple blacktip shark reporting categories and applying a latitudinal split following Leigh [2015] and Ovenden et al. [2007].Further information available through the Queensland Fisheries Summary Report https://www.daf.qld.gov.au/business-priorities/fisheries/monitoring-research/data/queensland-fisheries-summary-report

Queensland – Recreational Fishing (Catch). Data with high uncertainty (Residual Error >50 %) have been excluded and listed as unknown. More information available at: https://www.daf.qld.gov.au/business-priorities/fisheries/monitoring-research/monitoring-reporting/statewide-recreational-fishing-surveys  

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

Queensland – Commercial (Management Methods). Harvest strategies are available at: https://www.daf.qld.gov.au/business-priorities/fisheries/sustainable/harvest-strategy  

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

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

New South Wales - Recreational and Indigenous (catch). Given the distribution of Australian Blacktip Shark,  catches are likely to be negligible.

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.”

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.

Commercial catch of Australian Blacktip Shark - note confidential catch not shown

1. Boomer, JJ, Peddemors, V and Stow, AJ 2010, Genetic data show that Carcharhinus tilstoni is not confined to the tropics, highlighting the importance of a multifaceted approach to species identification. Journal of Fish Biology, 77: 1165-1172
2. Braccini, M, Kangas, M, Jaiteh, V and Newman S 2021, Quantifying the unreported and unaccounted domestic and foreign commercial catch of sharks and rays in Western Australia. Ambio 50: 1337-1350
3. Bradshaw, CJA, Field, IC, McMahon, CR, Johnson, GJ, Meekan, MG and Buckworth, RC 2013, More analytical bite in estimating targets for shark harvest. Marine Ecology Progress Series, 488: 221–232.
4. Dalton, S, Peddemors, V and Doak, C 2023, Shark Meshing (Bather Protection) Program 2022/23 Annual Performance Report. New South Wales Department of Primary Industries. 45 pp.
5. Harry, A 2011, Life histories of commercially important tropical sharks from the Great Barrier Reef World Heritage Area, PhD thesis, James Cook University, Townsville.
6. Harry, AV, Morgan, JAT, Ovenden, JR, Tobin, A, Welch, DJ and Simpfendorfer, C 2012, Comparison of the reproductive ecology of two sympatric Blacktip Sharks (Carcharhinus limbatus and Carcharhinus tilstoni) off north-eastern Australia with species identification inferred from vertebral counts. Journal of Fish Biology, 81: 1225–1233.
7. Johnson, G.J, Buckworth, RC, Lee, H, Morgan, J AT, Ovenden, JR and McMahon, CR 2017, A novel field method to distinguish between cryptic carcharhinid sharks, Australian blacktip shark Carcharhinus tilstoni and common blacktip shark C. limbatus, despite the presence of hybrids. Journal of Fish Biology, 90, 1, 39–60.
8. Last, PR and Stevens, JD 2009, Sharks and rays of Australia, CSIRO Publishing, Collingwood.
9. Leigh, GM 2015, Stock assessment of whaler and hammerhead sharks (Carcharhinidae and Sphyrinidae) in Queensland, Agri-Science Queensland, Department of Agriculture and Fisheries, Brisbane.
10. Macbeth, WG, Geraghty, PT, Peddemors, VM and Gray CA 2009, Observr-based study of targetted commercial fishing for large shark species in waters off northern New South Wales. INdustry & Investment NSW, Fisheries Final Report Series No. 114. 82 pp.
11. Molony, B, McAuley, R and Rowland, F 2013, Northern shark fisheries status report: Statistics only, in WJ Fletcher and K Santoro (eds) Status Reports of the Fisheries and Aquatic Resources of Western Australia 2012/13: The State of the Fisheries, Western Australian Department of Fisheries, Perth, 216–217.
12. Morgan, JA, Harry, AV, Welch, DJ, Street, R, White, J, Geraghty, PT, Macbeth, WG, Tobin, A, Simpfendorfer, CA and Ovenden, JR 2011, Detection of interspecies hybridisation in Chondrichthyes: hybrids and hybrid offspring between Australian (Carcharhinus tilstoni) and common (C. limbatus) Blacktip Shark found in an Australian fishery. Conservation Genetics, 13: 455–463.
13. Ovenden, JR, Street, R, Broderick, D, Kashiwagi, T and Salini, J 2007, Genetic population structure of Black-tip Sharks ( Carcharhinus tilstoni and C. sorrah) in northern Australia, in J Salini, R McAuley, S Blaber, RC Buckworth, J Chidlow, N Gribble, JR Ovenden, S Peverell, R Pillans, JD Stevens, I Stobutzki, C Tarca and TI Walker (eds), Northern Australian sharks and rays: the sustainability of target and bycatch species, phase 2, Fisheries Research and Development Corporation, Cleveland, Queensland.
14. Queensland Department of Agriculture and Fisheries 2020, Queensland Fisheries Harvest Strategies. Available at: https://www.daf.qld.gov.au/business-priorities/fisheries/sustainable/harvest-strategy (Accessed 18 October 2023).
15. Queensland Department of Agriculture and Fisheries 2021, Monitoring of Queensland’s shark catch for the net fisheries: summary report. Project Report. State of Queensland, Brisbane
16. Queensland Government 2023, Shark Control Program: Shark Catch Statistics by Year. Available at: https://www.data.qld.gov.au/dataset/shark-control-program-shark-catch-statistics (Accessed: 18 October 2023).
17. Ryan, KL, Hall, NG, Lai, EK, Smallwood, CB, Tate, A, Taylor, SM and Wise, BS 2019, Statewide survey of boat-based recreational fishing in Western Australia 2017/18. Fisheries Research Report No. 297, Department of Primary Industries and Regional Development, Western Australia.
18. Teixeira, D, Janes, R, and Webley, J 2021, 2019–20 Statewide Recreational Fishing Survey Key Results. Project Report, State of Queensland, Brisbane.
19. Usher, M, and Braccini, M 2021, Stock Status Summary - Australian Blacktip Shark (Carcharhinus tilstoni) North and West Coast stock stochastic stock reduction analysis. Unpublished Fishery Report