Australian Blacktip Shark (2020)
Date Published: June 2021
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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. 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 credit: Michael Usher, Department of Primary Industry and Resources, Northern Territory.
Stock Status Overview
|Western Australia||North Western Australia||Sustainable||
Biomass, fishing mortality, catch, catch rate
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.
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, though its implications for fisheries assessment and management remain poorly understood [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).
North Western Australia
The North Western Australia biological stock straddles two jurisdictions: The Northern Territory, west of the Wessel Islands–Western Australian border; and Western Australia. Domestic catches of Australian Blacktip Shark peaked in 2012 but have subsequently declined to relatively low levels. Changing operational practices in the NT Offshore Net and Line Fishery has greatly reduced the take of Australian Blacktip Shark in the Northern Territory. There has been little to no shark-targeted fishing occurring in the Northern Territory since 2012 as a result of declining shark fin prices and increasing value of Grey Mackerel (Scomberomorus semifasciatus), which is currently the main target species of this fishery. In this circumstance, the decline in catche has provided opportunity for the population of Australian Blacktip Shark to recover. Although there is uncertainty regarding species composition and the magnitude of historical catches of Blacktip Sharks from Western Australia, harvests of Australian Blacktip Shark in this jurisdiction have been negligible since April 2009 [Molony et al. 2013], allowing the biomass to increase.
A stock assessment was undertaken for the North Western Australia biological stock of Australian Blacktip Shark utilising a Stochastic Stock Reduction Analysis (SRA) model. The assessment estimated that in 2019 the harvest rate for Australian Blacktip Shark was 4 per cent of that required to reach MSY and that biomass was approximately 96 per cent of unfished levels [Usher et al. 2020]. The results of this assessment are supported by mark-recapture research undertaken for all species of Blacktip Shark in Northern Territory waters [Bradshaw et al. 2013]. This stock is not considered to be recruitment impaired and the current level of fishing is unlikely to cause the stock to become recruitment impaired.
On the basis of the evidence provided above, the North Western Australia biological stock of Australian Blacktip Shark is classified as a sustainable stock.
Blacktip Sharks biology [Harry, 2011, Harry et al. 2012, Last and Stevens 2009]
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
|Australian Blacktip Shark||
Carcharhinus tilstoni: Females 15 years, males 13 years; 2 000 mm TL
C. tilstoni: 5–6 years; females 1 350–1 400 mm, males 1 200 mm TL
Distribution of reported commercial catch of Australian Blacktip Sharks
|Licence (boat-based sector)|
|Effort limits (individual transferable effort)|
|Licence (boat-based sector)|
|Recreational||No Australian Blacktip Shark caught from boats [Ryan et al. 2019], shore-based catches are undetermined|
Western Australia – Recreational (Management methods) A recreational fishing from boat licence is required for recreational fishing from a powered vessel in Western Australia.
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 commercial fisheries with less than seven active fishers are not presented due to the Privacy Act.
Recreational and Indigenous (catch) Given the offshore distribution of Sandbar Shark, near-shore catches are likely to be negligible.
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”.
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 Blacktip Sharks - note confidential catch not shown
- 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.
- de Faria, F 2012 Recreational fishing of sharks in the Great Barrier Reef World Heritage Area: species composition and incidental capture stress, Masters thesis, James Cook University
- Harry, A, 2011, Life histories of commercially important tropical sharks from the Great Barrier Reef World Heritage Area, PhD thesis, James Cook University, Townsville.
- 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.
- 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.
- Last, PR and Stevens, JD (2009) Sharks and rays of Australia, CSIRO Publishing, Collingwood.
- Leigh, GM , 2015, Stock assessment of whaler and hammerhead sharks (Carcharhinidae and Sphyrinidae) in Queensland, Agri-Science Queensland, Department of Agriculture and Fisheries, Brisbane.
- 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.
- 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.
- 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.
- QFish, Department of Agriculture and Fisheries, www.qfish.gov.au
- Usher, M, Saunders, T and Braccini, M (2020) Stock Status Summary - 2020 Australian Blacktip Shark (Carcharhinus tilstoni) North and West Coast stock stochastic stock reduction analysis. Unpublished Fishery Report