BLACKTIP SHARKS (2018)
Carcharhinus sorrah, Carcharhinus tilstoni, Carcharhinus limbatus
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Blacktip Sharks are found along Australia’s northern coastline. The stock in east coast fisheries off NSW and QLD is sustainable. The north and western stock in NT and WA fisheries is also sustainable. The stock in QLD’s Gulf of Carpentaria is undefined. This assessment combines Australian Blacktip Shark, Common Blacktip Shark and Spot-Tail Shark.
Stock Status Overview
|Northern Territory||North and West Coast||BF, DF, ONLF, SMF, BNF, CNF, SPDF||Sustainable||Catch, mark recapture, CPUE, pup production|
|Northern Territory||Gulf of Carpentaria||ONLF||Undefined||Catch, MSY|
- Barramundi Fishery (NT)
- Bait Net Fishery (NT)
- Coastal Net Fishery (NT)
- Demersal Fishery (NT)
- Offshore Net and Line Fishery (NT)
- Spanish Mackerel Fishery (NT)
- Small Pelagic Developmental Fishery (NT)
In the context of Australian fisheries, the Blacktip Shark species complex, part of the family Carcharhinidae (whaler sharks), comprises three species: Carcharhinus tilstoni (Australian Blacktip Shark), C. limbatus (Common Blacktip Shark) and C. sorrah (Spottail Shark). Whereas C. tilstoni and C. sorrah are distributed only within Australian and Indo–West Pacific waters, respectively, C. limbatus is globally distributed in tropical and warm temperate waters. In Australian waters, genetic studies have identified two biological stocks of C. tilstoni (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), three biological stocks of C. limbatus (one across Western Australia and the Northern Territory, one in the Gulf of Carpentaria, and one on the east coast of Queensland and New South Wales) and a single biological stock of C. sorrah across northern Australia [Ovenden et al. 2007]. Stock boundaries between the western biological stocks of C. tilstoni and C. limbatus and those in the Gulf of Carpentaria are uncertain.
Carcharhinus limbatus and C. tilstoni are similar in appearance and can only be taxonomically differentiated by genetic analyses, precaudal vertebral counts or, in certain size classes, their differences in size of maturity [Harry AV 2011]. There are two new techniques - one using machine learning models and the other using differences in pelvic fin colouration - that may assist in distinguishing between these two species, however, accurate field identification remains difficult and is not practical during fishing operations [Johnson et al. 2017]. Hybridisation between C limbatus and C. tilstoni has also been recorded, though the impacts of this remain poorly understood [Harry et al. 2012, Johnson 2017, Morgan et al. 2011]. Because a suite of three species of differing stock structures is grouped together for this assessment, stocks have been assessed on the finest known scale—using the three biological stock areas identified for C. limbatus.
Here, assessment of stock status for the Blacktip Shark multispecies group is presented at the biological stock level—North and West Coast, Gulf of Carpentaria, and East Coast.
Gulf of Carpentaria
The Queensland Department of Agriculture and Fisheries commissioned a scientific assessment of shark stocks which provided MSY per annum estimates for C. tilstoni and C. sorrah in the Gulf of Carpentaria. This assessment produced qualified MSY estimates of 95 tonnes (t) for C. tilstoni and 29.4 t for C. sorrah [Leigh GM 2015]. This report also, however, acknowledged a number of data limitations for Queensland fisheries, particularly with respect to accuracy of species identifications and the quantity and reliability of available catch data.
In 2017, 103 t of C. tilstoni and 9 t of C. sorrah were reported from the Gulf of Carpentaria Inshore Finfish Fishery (GOCIFFF); catches that were above and below the respective MSY estimates. Species-specific data for the fishery showed that over the past 10 years the annual catches of C. sorrah (9–34 t) exceeded the MSY estimate twice, while catch of C. tilstoni (54–160 t) exceeded MSY seven times over the same period. An estimated 38–125 t was reported from the GOCIFFF each year for the period 2007–17 under the ‘Blacktip Whaler Shark’ catch category that includes Graceful Sharks (C. amblyrhynchoides). At present, catch reported in the ‘Blacktip Whaler Shark’ category cannot be differentiated into individual species.
The inability to assign more multispecies catch records to Blacktip Shark species makes it difficult to identify catch and effort trends for this species complex. Consequently, current catch levels and their impact on the biological stock are unknown, and there is insufficient information to confidently classify the status of this stock. This situation is expected to improve through time with the introduction of a new Shark and Ray logbook into the Gulf of Carpentaria on 1 January 2018, which limits the ‘Blacktip Whaler’ category to C. limbatus and C. tilstoni only and lists Graceful sharks (C. amblyrhynchoides) and Spottail shark (C. sorrah) individually.
On the basis of the evidence provided above, the Gulf of Carpentaria multispecies biological stock is classified as an undefined stock.
North and West Coast
The North and West Coast biological stock straddles two jurisdictions: The Northern Territory, west of the Wessel Islands–Western Australian border; and Western Australia.
In 2011, a stock assessment was undertaken for this biological stock utilising stock reduction analysis models, which rely on catch per unit effort data. The results from these models at the time estimated that the harvest rates for all species within the complex were less than 20 per cent of that required to reach maximum sustainable yield (MSY) and current pup production was approximately 80 per cent of unfished levels [Grubert et al. 2013]. Results from a mark-recapture study done for all species of Blacktip Shark in Northern Territory waters supports the stock assessment results [Bradshaw et al. 2013]. Catches for this Blacktip Shark stock peaked in 2012 but have subsequently decreased to relatively low levels. This decrease in catch was driven by changing operational practises in the Offshore Net and Line Fishery [Northern Territory Government 2017].
Although there is uncertainty regarding species composition and the magnitude of historical catches of Blacktip Sharks from Western Australia, these species have not been harvested in this jurisdiction since April 2009 [Molony et al. 2013], allowing the biomass to increase.
The most recent assessment [Grubert et al. 2013] estimated that biomass in 2011 was 80 per cent of the unfished 1970 level. As current catches are well below those recorded in 2011, when the catches were assessed as sustainable, it is unlikely that current catches are having a reductive impact on the stock. The 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 and West Coast multispecies biological stock is classified as a sustainable stock.
Blacktip Sharks biology [Harry et al. 2012, Harry AV 2011, Last and Stevens 2009]
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
|BLACKTIP SHARKS||C. tilstoni: Females 15 years, males 13 years, 2 000 mm TL C. limbatus: Maximum age unknown, 2 500 mm TL C. sorrah: Females 14 years, males 9 years, 1 600 mm TL||C. tilstoni: 5–6 years, females 1 350–1 400 mm, males 1 200 mm TL C. limbatus: females unknown, males 1 800 mm C. sorrah: 2–3 years, both sexes 900–950 mm TL|
|Hook and Line|
|Total allowable catch|
|Commercial||285.71kg in BF, 140.00kg in BNF, 1.40t in CNF, 77.40t in ONLF|
- Barramundi Fishery (NT)
- Bait Net Fishery (NT)
- Coastal Net Fishery (NT)
- Offshore Net and Line Fishery (NT)
Western Australia – Commercial (Fishing methods) No commercial fishing has occurred in the Western Australia jurisdiction since April 2009.
Western Australia – Recreational (Management methods) A recreational fishing from boat licence is required for recreational fishing from a powered vessel in Western Australia.
Western Australia – Indigenous (Management methods) 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.
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.
Queensland – Indigenous (Management methods) In Queensland, under the Fisheries Act 1994 (Qld), Indigenous fishers in Queensland are able to use prescribed traditional and non-commercial fishing apparatus in waters open to fishing. Size and possession limits, and seasonal closures do not apply to Indigenous fishers. Further exemptions to fishery regulations may be applied for through permits.
New South Wales – Indigenous (Management methods) (a) Aboriginal Cultural Fishing Interim Access Arrangement—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 for themselves; (b) The Aboriginal cultural fishing authority is the authority that Indigenous persons can apply to take catches outside the recreational limits under the Fisheries Management Act 1994 (NSW), Section 37 (1d) (3)(9), Aboriginal cultural fishing authority; and (c) In cases where the Native Title Act 1993 (Cth) applies fishing activity can be undertaken by the person holding native title in line with S.211 of that Act, which provides for fishing activities for the purpose of satisfying their personal, domestic or non-commercial communal needs. In managing the resource where native title has been formally recognised, the native title holders are engaged with to ensure their native title rights are respected and inform management of the State's fisheries resources.
New South Wales commercial fisheries with less than seven active fishers are not presented due to the Privacy Act.
- 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.
- Grubert, MA, Saunders, TM, Martin, JM, Lee, HS and Walters, CJ 2013, Stock assessments of selected Northern Territory fishes, Fishery report 110, Northern Territory Government, Darwin.
- Harry, AV 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.
- Harry, AV, Tobin, AJ, Simpfendorfer, CA, Welch, DJ, Mapleston, A, White, J, Williams, AJ and Stapley, J 2011, Evaluating catch and mitigating risk in a multispecies, tropical, inshore shark fishery within the Great Barrier Reef World Heritage Area. Marine and Freshwater Research 62:710–721.
- 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.
- Macbeth, WG, Butcher, PA, Collins, D, McGrath, SP, Provost, SC, Bowling, AC, Geraghty, PT and Peddemors, VM 2018, Improving reliability of species identification and logbook catch reporting by commercial fishers in an Australian demersal shark longline fishery. Fisheries Management and Ecology, 25: 186-202.
- Macbeth, WG, Geraghty, PT, Peddemors, VM, and Gray, CA 2009, Observer-based study of targeted commercial fishing for large shark species in waters of New South Wales, Industry and Investment New South Wales. Fisheries Final Report Series 82.
- 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.
- Northern Territory Government (NTG) 2017, Status of key Northern Territory fish stocks report 2015, Fishery report 118, Department of Primary Industry and Fisheries, Darwin.
- 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.
- Queensland Department of Agriculture and Fisheries (QDAF) 2018, Qfish, State of Queensland, Department of Agriculture and Fisheries, Brisbane.
- Ryan K, Hall N, Lai E, Smallwood C, Taylor S, Wise B. 2017. Statewide survey of boat-based recreational fishing in Western Australia 2015/16. Fisheries Research Report No. 287, Department of Primary Industries and Regional Development, Western Australia.