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Blue Threadfin is a short-lived, fast-growing species with low fishing pressure. It is classified as a sustainable stock in QLD and the NT, and as negligible in WA.

Blue Threadfin is widely distributed in coastal waters throughout the Indo-West Pacific. Its range extends from the Persian Gulf eastward around the Indian Ocean rim to the Malay Peninsula, Gulf of Thailand, mouth of the Mekong River delta, China, Taiwan Province, Philippines, through Indonesia to southern New Guinea and northern Australia and in the north to southern Japan [Carpenter and Niem 2001]. In Australia, Blue Threadfin extend from the Exmouth Gulf region in Western Australia around the northern coastline to Sandy Cape in southern Queensland [Carpenter and Niem 2001].

A number of methods (genetics, otolith stable isotope chemistry, parasite abundances, life history and tag-recapture data) have been used to examine population structure in the Blue Threadfin [Zischke et al. 2009; Welch et al. 2010; Horne et al. 2011; Moore et al. 2011; Newman et al. 2011; Ballagh et al. 2012; Horne et al. 2012; Horne et al. 2013]. These studies have shown that adult Blue Threadfin do not move very far and tend to form localised populations around northern Australia. A tagging study on Blue Threadfin on the east coast of Australia found that approximately70% of tagged Blue Threadfin were recaptured within 10 km of their release location [Zischke et al. 2009]. Blue Threadfin comprise numerous populations across northern Australia that are separated by 10 to 100 km or by large, coastal geographical features, and which exhibit high levels of self-recruitment [Zischke et al. 2009; Welch et al. 2010; Horne et al. 2011; Moore et al. 2011; Newman et al. 2011; Ballagh et al. 2012; Horne et al. 2012; Horne et al. 2013]. There is a high likelihood of separate biological stocks occurring within each jurisdiction; however, the boundaries between possible stocks and whether they might vary over time, are not known. The status of individual biological stocks cannot be determined as biological and catch-and-effort information are not collected at these finer spatial scales.

Here, assessment of stock status is presented at the management unit level in Queensland—Gulf of Carpentaria and East Coast Queensland, and at the jurisdictional level—Western Australia and Northern Territory.

Western Australia

Stock status for the Western Australian jurisdictional stock is reported as negligible due to historically low levels of catch in this jurisdiction and the stock has generally not been subject to targeted fishing. Blue Threadfin is caught primarily within the North Coast Nearshore and Estuarine Resource (NCNER) by the Kimberley Gillnet and Barramundi Managed Fishery (KGBMF) in small quantities as by-product [Trinnie et al. 2023] when targeting Barramundi or King Threadfin. The stocks of Barramundi and King Threadfin are assessed as sustainable stocks in Western Australia. Consequently, the level of risk associated with the sustainability of Blue Threadfin in the NCNER is considered to be low. Catch levels of Blue Threadfin across the NCNER over the last 10 years (2013–22) have ranged from 3.8–6.3 t, with a mean annual catch of 5.5 t. This is a decline on the averages catches across the previous 10 years (9.1 t). In recent years, overall commercial fishing effort directed towards fish stocks in the NCNER has declined markedly. This reflects, at least in part, the removal of two commercial gillnet licenses in 2013 from the Broome coast area of the fishery [Newman et al. 2022], along with closures in the mid-2000s to commercial fishing along a large area of the Pilbara coast and Eighty-mile beach. This large area of the fishery, which is closed to commercial fishing, only experiences recreational, charter, and indigenous fishing. Catches of Blue Threadfin remain a minor component of recreational and charter landings throughout the North Coast Bioregion of WA. The combined recreational and charter catch of Blue Threadfin is larger than the commercial catch (on average approximately 75% of the total catch in past 10 years).

Blue Threadfin biology [Stanger 1974; Bibby et al. 1997; McPherson 1997; Pember 2006; Welch et al. 2010]

Distribution of reported commercial catch of Blue Threadfin

Northern Territory – Charter (management methods). Note Charter operators in the Northern Territory are under the same management methods as the recreational sector but have the additional restrictions of limited licences and passenger numbers.

Northern Territory - Indigenous (management methods). The Fisheries Act 1988 (NT), specifies that: “Unless expressly provided otherwise, nothing in this Act derogNorthern Territory – Charter (Management Methods). Note Charter operators in the Northern Territory are under the same management methods as the recreational sector but have the additional restrictions of limited licences and passenger numbers.

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.”

Queensland – Indigenous (Management Methods). For more information see: https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing

Queensland – Commercial (Catch). Queensland commercial and charter data have been sourced from the commercial fisheries logbook program. 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 are based at the whole of Queensland level and derived from statewide recreational fishing surveys. Where possible, estimates have been converted to weight (tonnes) using best known conversion multipliers. Conversion factors may display regional or temporal variability. In the absence of an adequate conversion factor, data are presented as number of fish.

Western Australia – Recreational (Catch). Boat-based recreational catch between 1 September 2020 and 31 August 2021 from Ryan et al. [2022]. Please note that catches of Blue Threadfin are underestimates as shore-based and boat-based fishers that only operated in freshwater were out of scope of the survey.

Western Australia – Recreational (Management Methods). A Recreational Fishing from Boat Licence is required for the use of a powered boat to fish or to transport catch or fishing gear to or from a land-based fishing location.

Western Australia – Indigenous (Management Methods). Subject to application of 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.

Commercial catch of Blue Threadfin - note confidential catch not shown.

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