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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).

Gulf of Carpentaria

The Gulf of Carpentaria management unit straddles two jurisdictions: The Northern Territory, east of the Wessel Islands-Queensland border and Queensland, west of Cape York to the Northern Territory border. Most Australian Blacktip Sharks in this management unit are caught by Queensland Fisheries (Queensland 34 t; Northern Territory 1.4 t). Harvest has declined in recent years, however this is due to poor market demand for shark products and is unlikely to be related to biomass declines.

The Offshore Net and Line Fishery (ONLF) is responsible for the majority of the Australian Blacktip Shark harvest in the Northern Territory. Australia Blacktip Shark harvest in the Northern Territory portion of the Gulf of Carpentaria has ranged from 0.7 to 15 t, at an annual average of 3.4 t, in the last 10 years (2012/13-2021/22). Changing operational practices in the Northern Territory Offshore Net and Line Fishery has have 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 the increasing value of Grey Mackerel (Scomberomorus semifasciatus), which is currently the main target species of this fishery.

The last Queensland stock assessment for Australian Blacktip Shark was completed in 2015 and based on data up until 2013 [Leigh 2015]. This assessment produced Maximum Sustainable Yield (MSY) estimates for the Gulf of Carpentaria ranging from 95 t to 513 t. The higher bound of the MSY estimate sits well above the annual commercial harvests reported in the Gulf of Carpentaria Inshore Fishery (GoCIF); the primary fishery accessing this species in the Gulf of Carpentaria. In 2021–22 the commercial harvest of Australian Blacktip Shark was 34 t, below the 10-year harvest average of 121 t (range = 34 to 220).

While noting the above, historic catch data for this management unit has poor species resolution and deficiencies exist in terms of the catch composition and the quantity/quality of the available data. Reporting and datasets for the Blacktip Shark complex have improved in Queensland with the introduction of a Shark and Ray specific logbook on 1 January 2018, and biological monitoring programs [Queensland Department of Agriculture and Fisheries, 2021]. However, there remains a degree of uncertainty in the level of fishing pressure exerted on Australian Blacktip Shark in the Gulf of Carpentaria. This uncertainty makes it difficult to accurately classify the status of the management unit. 

On the basis of the evidence provided above, Australian Blacktip Shark in the Gulf of Carpentaria management unit is classified as an undefined stock.

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 Northern Territory Offshore Net and Line Fishery have 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 the increasing value of Grey Mackerel (Scomberomorus semifasciatus), which is currently the main target species of this fishery. In this circumstance, the decline in catch 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; Braccini et al. 2021]. These negligible harvests are expected to allow for increasing biomass levels. In addition, recreational catches are negligible [Ryan et al 2019.] 

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 2021 the harvest rate for Australian Blacktip Shark less than 3% of that required to reach MSY and that biomass was approximately 89% of unfished levels [Northern Territory Government, unpublished]. 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 depleted 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.

[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

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