*

Blue Threadfin is a short-lived, fast-growing species with low susceptibility to 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 ~70 per cent 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 10–100s 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 in each jurisdiction; however, the boundaries between possible stocks and whether they might vary over time,  are not known. It is difficult to collect the biological and catch-and-effort information to determine the status of individual biological stocks.

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. The stock has generally not been subject to targeted fishing and the species is caught as a byproduct when targeting King Threadfin within the Kimberley Gillnet and Barramundi Managed Fishery (KGBMF). The Western Australian commercial catch has been low and stable for the past six years (2014–19), ranging from 1.2–1.8 t, with a mean annual catch of 1.5 t. The recent catches from 2014–2019 are well below the average of 5.2 t for the 10-year period from 2004–2013. This is due to low effort levels in the fishery [Newman et al. 2020] following the removal of two fishing licenses from the Broome coast area. The Broome coast area has been closed to commercial fishing since late 2013. Blue Threadfin is not a major component of recreational landings although the recreational and charter catch of Blue Threadfin is larger than the commercial catch (~6 t, combined recreational and charter). This catch is low given the large spatial extent of recreational fishing activity. Fishing is unlikely to be having a negative impact on the stock.

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 - note confidential catch not shown

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.

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

Western Australia – Recreational (catch) Boat-based recreational catch between 1 September 2015 and 31 August 2016 from Ryan et al. [2019]. 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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