*

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.

Northern Territory

Northern Territory. The recreational harvest is significant, at around 40 per cent of the overall harvest of this species [West et al. 2012]. The majority of the recreational take of Blue Threadfin (85 per cent) is captured around the greater Darwin area, within a radius of about 150 km of this population centre [West et al. 2012]. The recreational catch within this region in 2015 was 5.2 t [Matthews et al. 2019].The spatial distribution of the commercial catch is similar, with some harvest from the northeast coast and the southern Gulf of Carpentaria. There are no estimates of the Indigenous harvest of Blue Threadfin (as a unique species) in the Northern Territory. However, the annual harvest of "Threadfin Salmons" (i.e. 8 565 individual fishes) reported by Henry and Lyle [2003] provides some indication of the scale of the combined harvest of Blue Threadfin and King Threadfin (Polydactylus macrochir) by Indigenous fishers in this jurisdiction. 

The commercial catch of Blue Threadfin peaked at 26.9 t in 2011. Annual catches in the decade spanning 2010–19 averaged 13.6 t, with the catch in 2019 being 4.3 t. A preliminary assessment using catch data applied to a modified catch-MSY model (developed by Martell and Froese [2013] and modified by Haddon et al. [2018]), suggests that the relative biomass (29.5 t) of Blue Threadfin at in 2019 was above the target biomass (i.e. 50 per cent of 1983 biomass) [Grubert and Saunders, unpublished]. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. The same assessment also indicated that the harvest rate in 2019 was just over half of the target rate. The above evidence indicates that the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired.

On the basis of the evidence provided above, Blue Threadfin in the Northern Territory is classified as a 

sustainable 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.

1. Ballagh, AC, Welch, DJ, Newman, SJ, Allsop, Q and Stapley, JM 2012, Stock structure of the blue threadfin (Eleutheronema tetradactylum) across northern Australia derived from life-history characteristics. Fisheries Research 121–122: 63–72.
2. Bibby, JM, Garrett, RN, Keenan, CP, McPherson, GR and Williams, LE 1997, Biology and Harvest of Tropical Fishes in the Queensland Gulf of Carpentaria Gillnet Fishery. Brisbane: Department of Primary Industries.
3. Carpenter, KE and Niem, VH (eds.) 2001, FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Volume 5. Bony fishes part 3 (Menidae to Pomacentridae). Rome, FAO, pp. 2791–3380.
4. Haddon M, Punt A and Burch P 2018, simpleSA: A package containing functions to facilitate relatively simple stock assessments. R package version 0.1.18.
5. Henry, GW, and Lyle, JM, 2003, The National Recreational and Indigenous Fishing Survey. Report to the Fisheries Research and Development Corporation on project number 99/158.
6. Horne, JB, Momigliano, P, van Herwerden, L and Newman, SJ 2013, Murky waters: searching for structure in genetically depauperate blue threadfin populations of Western Australia. Fisheries Research 146: 1–6.
7. Horne, JB, Momigliano, P, Welch, DJ, Newman, SJ and van Herwerden, L 2011, Limited ecological population connectivity suggests low demands on self-recruitment in a tropical inshore marine fish (Eleutheronema tetradactylum: Polynemidae). Molecular Ecology 20 (11): 2291–2306.
8. Horne, JB, Momigliano, P, Welch, DJ, Newman, SJ and van Herwerden, L 2012, Searching for common threads in threadfins: phylogeography of Australian polynemids in space and time. Marine Ecology Progress Series 449: 263–276.
9. Martell, S and R. Froese 2013, A simple method for estimating MSY from catch and resilience. Fish and Fisheries 14: 504–514
10. Matthews, S. R., Penny, S. S and Steffe A. (2019). A Survey of Recreational Fishing in the Greater Darwin Area 2015. Northern Territory Government, Australia. Fishery Report No 121.
11. McPherson, GR 1997, Reproductive biology of five target fish species in the gulf of Carpentaria inshore gillnet fishery. In: Garrett, R.N. 1997 Biology and Harvest of tropical fishes in the Queensland Gulf of Carpentaria gillnet fishery. pp 87–104.
12. Moore, BR, Stapley, J, Allsop, Q, Newman, SJ, Ballagh, A, Welch, DJ and Lester, RJG 2011, Stock structure of blue threadfin Eleutheronema tetradactylum across northern Australia, as indicated by parasites. Journal of Fish Biology 78 (3): 923–936.
13. Newman, SJ, Mitsopoulos, G, Skepper, C and Wiberg, L 2020, North Coast Nearshore and Estuarine Resource Status Report 2019. pp. 153–159. In: Gaughan, D.J. and Santoro, K. (eds.). 2020 Status Reports of the Fisheries and Aquatic Resources of Western Australia 2018/19: The State of the Fisheries. Department of Primary Industries and Regional Development, Western Australia, Perth, Australia. 291p.
14. Newman, SJ, Pember, MB, Rome, BM, Mitsopoulos, GEA, Skepper, CL, Allsop, Q, Saunders, T, Ballagh, AC, van Herwerden, L, Garrett, RN, Gribble, NA, Stapley, JM, Meeuwig, JJ, Moore, BR and Welch, DJ 2011, Stock structure of blue threadfin Eleutheronema tetradactylum across northern Australia as inferred from stable isotopes in sagittal otolith carbonate. Fisheries Management and Ecology 18 (3): 246–257.
15. Northern Territory Blue Threadfin Stock Status Summary - 2020. Unpublished Fishery Report
16. Pember, MB 2006, Characteristics of fish communities in coastal waters of north-western Australia, including the biology of the threadfin species Eleutheronema tetradactylum and Polydactylus macrochir. 297. PhD Thesis, Murdoch University, Western Australia: Murdoch University.
17. QFish, Department of Agriculture and Fisheries, www.qfish.gov.au
18. Ryan, KL, Hall, NG, Lai, EK, Smallwood, CB, Tate, A, Taylor, SM and Wise, BS 2019, Statewide survey of boat-based recreational fishing in Western Australia 2017/18. Fisheries Research Report No. 297. Department of Primary Industries and Regional Development, Government of Western Australia, Perth. 
19. Stanger, JD 1974, A study of the growth, feeding, and reproduction of the threadfin, Eleutheronema tetradactylus (Shaw). 126. Hons Thesis, Department of Zoology. James Cook University, Queensland.
20. Webley, J, McInnes, K, Teixeira, D, Lawson, A and Quinn, R 2015, Statewide Recreational Fishing Survey 2013–14. Department of Agriculture and Fisheries, Brisbane.
21. Welch, DJ, Ballagh, AC, Newman, SJ, Lester, RJG, Moore, BR, van Herwerden, L, Horne, J, Allsop, Q, Saunders, T, Stapley, JM and Gribble, NA 2010, Defining the Stock Structure of Northern Australia's Threadfin Salmon Species. In Fish and Fisheries Research Centre Technical Report, 192. Townsville: James Cook University.
22. West, LD, Lyle, JM, Matthews, SR, Stark, KE, Steffe AS, 2012, Survey of recreational fishing in the Northern Territory, 2009–10. Northern Territory Government, Australia. Fishery Report No. 109.
23. Whybird, O, Trinnie, F, Penny, S and Newman, S, 2018, Blue Threadfin Eleutheronema tetradactylum, in Carolyn Stewardson, James Andrews, Crispian Ashby, Malcolm Haddon, Klaas Hartmann, Patrick Hone, Peter Horvat, Stephen Mayfield, Anthony Roelofs, Keith Sainsbury, Thor Saunders, John Stewart, Simon Nicol and Brent Wise (eds) 2018, Status of Australian fish stocks reports 2018, Fisheries Research and Development Corporation, Canberra.
24. Zischke, MT, Cribb, TH, Welch, DJ, Sawynok, W and Lester RJG 2009, Stock structure of blue threadfin on the Queensland east coast as determined by parasites and conventional tagging. Journal of Fish Biology 75: 156–171.