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Blue Threadfin (2018)

Eleutheronema tetradactylum

  • Olivia Whybird (Department of Agriculture and Fisheries, Queensland)
  • Fabian Trinnie (Department of Primary Industries and Regional Development, Western Australia)
  • Shane Penny (Department of Primary Industry and Resources, Northern Territory)
  • Stephen Newman (Department of Primary Industries and Regional Development, Western Australia)
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Summary

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.

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Stock Status Overview

Stock status determination
Jurisdiction Stock Fisheries Stock status Indicators
Northern Territory Northern Territory BF, CLF, ONLF, ACL, BNF, CNF Sustainable Catch, estimated harvest rate
Queensland East Coast Queensland ECIFFF Sustainable Catch, effort, CPUE
Queensland Gulf of Carpentaria GOCIFFF Sustainable Catch, effort, CPUE
Western Australia Western Australia KGBMF Negligible Catch
ACL
Aboriginal Coastal License (NT)
BF
Barramundi Fishery (NT)
BNF
Bait Net Fishery (NT)
CLF
Coastal Line Fishery (NT)
CNF
Coastal Net Fishery (NT)
ECIFFF
East Coast Inshore Fin Fish Fishery (QLD)
GOCIFFF
Gulf of Carpentaria Inshore Fin Fish Fishery (QLD)
KGBMF
Kimberley Gillnet and Barramundi Managed Fishery (WA)
ONLF
Offshore Net and Line Fishery (NT)
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Stock Structure

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 [Ballagh et al. 2012, Horne et al. 2011, Horne et al. 2012, Horne et al. 2013, Moore et al. 2011, Newman et al. 2011, Welch et al. 2010, Zishke et al. 2009]. 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 [Ballagh et al. 2012, Horne et al. 2011, Horne et al. 2012, Horne et al. 2013, Moore et al. 2011, Newman et al. 2011, Welch et al. 2010, Zishke et al. 2009]. There is a high likelihood of separate biological stocks occurring in each jurisdiction; however, the boundaries between possible stocks 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.

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Stock Status

East Coast Queensland

Blue Threadfin is primarily caught in the East Coast Inshore Fin Fish Fishery (using nets), but tends not to be a primary target. The species is occasionally caught in the East Coast Line Fishery.

Catch and catch rates decreased in 2016 and 2017 following the introduction of three new net closure areas in November 2015, along with a buy-back scheme for net licenses. Average annual catch over 2006–15, prior to this management change, for the Net Free Zones was Capricorn Coast 34 t, Trinity Bay 5 t, St Helens 3.2 t [QDAF 2018]. When catches from these Net Free Zones are excluded from the whole time series the average catch for 2016 and 2017 was 61 t compared to the 2006–15 average of 113 t [QDAF 2018].

Commercial un-standardised catch rates rose steeply from 6 to 14 kg per 100 m of net from 1988 to 1994, and stabilised at a rate of 10–12 kg per 100 m net until 2015. After some of the productive areas for this species were closed in November 2015, commercial catch rates decreased to 6.5 and 6.7 kg per 100 m in 2016 and 2017 respectively, but remain above 50 per cent of the long-term average. The above evidence indicates the biomass of the stock is unlikely to be depleted and that recruitment is unlikely to be impaired

Blue Threadfin is a short lived, fast growing species, that has a low susceptibility to fishing pressure [Welsh et al. 2010], despite its high discard mortality and the minimum legal size being less than the size at which males transition to females [Bibby et al. 1997]. Fishing pressure has decreased since management changes in 2015, with fewer licences and fishing days, and additional areas protected from commercial harvest. In 2013, a reported 4 368 net fishing days were recorded, declining to 3 352 days in 2017. Recreational catches have also declined from approximately 17 000 harvested in 2009–10 to 14 000 fish in 2012-13 [Webley et al. 2015]. 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, the East Coast Queensland management unit is classified as a sustainable stock.

Gulf of Carpentaria

In the Gulf of Carpentaria Blue Threadfin is harvested by the Gulf of Carpentaria Inshore Fin Fish Fishery. The commercial catch has been variable since the commencement of compulsory commercial reporting (1989). Record high catches of around 124 t were reported in 1999 and 2004. In 2017 the commercial catch was 74 t which is 37 per cent higher than the previous 10 year (2007–16) catch average. Nominal catch rates of this species fluctuated from about 4 kg per 100 m net in 1988 to 12 kg per 100 m net in 1999. Since 2001, the nominal catch rate from the fishery has been around 8 kg per 100 m net, rising to 10 kg per 100 m net in 2017, the second highest rate of the time series. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired.

The species is considered to have a low susceptibility to fishing pressure [Welch et al. 2010] as it is a short-lived and fast-growing species. Fishing pressure has fluctuated with harvest levels but has generally decreased over the recent decade. A peak of 78 active commercial licences and 3 111 days fished occurred in 2004. In 2017 there were 56 active licences and catch was reported on 1 714 days. Queensland recreational harvest in 2013–14 was approximately 16 000 fish which is only 25 per cent higher than the estimated harvest during 2010–11 [Webley et al. 2015]. 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, the Gulf of Carpentaria (Queensland) management unit is classified as a sustainable stock.

Northern Territory

Blue Threadfin is incidentally caught in several inshore fisheries operating across the Northern Territory. The recreational harvest is significant, at around 40 per cent of the overall harvest of this species [NTG unpublished]. The majority of the recreational take of Blue Threadfin (85 per cent) is taken around the greater Darwin area, within a radius of approximately 150 km of this population center [West et al. 2012]. 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 in the Northern Territory. Due to the lack of a long-term time series of recreational and Indigenous catches, the assessment presented here is based on data from commercial logbooks.

The commercial catch of Blue Threadfin peaked at 100 t in 1996. Annual catches in the decade spanning 2008–17 averaged 23 t, with the catch in 2017 being 11.6 t. A preliminary assessment using catch data with a catch-MSY model, modified from Martell and Froese (2013), suggests that the predicted relative biomass (139 t) of Blue Threadfin at the conclusion of 2017 was slightly below the target biomass (i.e. 50 per cent of 1983 biomass). 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 2017 was below the target rate (0.18 per annum). 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.

Western Australia

Stock status for the Western Australia jurisdictional stock is reported as Negligible due to historically low catches in this jurisdiction. The stock has generally not been subject to targeted fishing. The Western Australian commercial catch over the 10 year period from 2008–17 has averaged less than 150 kg per annum [Newman et al. 2018]. 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 (~7 tonnes [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.

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Biology

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

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
Blue Threadfin 7 years, 880 mm FL Variable on location and year Females: 2 to 4 years, 208–543 mm FL
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Distributions

Distribution of reported commercial catch of Blue Threadfin - note confidential catch not shown

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Tables

Fishing methods
Western Australia Northern Territory Queensland
Commercial
Hook and Line
Gillnet
Pelagic Gillnet
Cast Net
Beach Seine
Indigenous
Spearfishing
Traps and Pots
Handline
Recreational
Handline
Spearfishing
Charter
Handline
Management methods
Method Western Australia Northern Territory Queensland
Charter
Bag and possession limits
Limited entry
Passenger restrictions
Size limit
Spatial closures
Spatial zoning
Commercial
Gear restrictions
Limited entry
Size limit
Spatial closures
Spatial zoning
Temporal closures
Vessel restrictions
Recreational
Bag and possession limits
Size limit
Spatial closures
Temporal closures
Active vessels
Western Australia Northern Territory Queensland
27 in Charter, <3 in KGBMF 12 in ACL, 14 in BF, 13 in BNF, 14 in CLF, 3 in CNF, 7 in ONLF 136 in ECIFFF, 56 in GOCIFFF
ACL
Aboriginal Coastal License (NT)
BF
Barramundi Fishery (NT)
BNF
Bait Net Fishery (NT)
Charter
Tour Operator (WA)
CLF
Coastal Line Fishery (NT)
CNF
Coastal Net Fishery (NT)
ECIFFF
East Coast Inshore Fin Fish Fishery (QLD)
GOCIFFF
Gulf of Carpentaria Inshore Fin Fish Fishery (QLD)
KGBMF
Kimberley Gillnet and Barramundi Managed Fishery (WA)
ONLF
Offshore Net and Line Fishery (NT)
Catch
Western Australia Northern Territory Queensland
Commercial 795.50kg in ACL, 1.51t in BF, 4.59t in BNF, 654.67kg in CLF, 1.26t in CNF, 534.00kg in ONLF 58.00t in ECIFFF, 74.38t in GOCIFFF
Indigenous Unknown Unknown
Recreational 7.806 t 19 t +/- 9 t Gulf of Carpentaria, 15 t +/- 7 t East Coast
ACL
Aboriginal Coastal License (NT)
BF
Barramundi Fishery (NT)
BNF
Bait Net Fishery (NT)
CLF
Coastal Line Fishery (NT)
CNF
Coastal Net Fishery (NT)
ECIFFF
East Coast Inshore Fin Fish Fishery (QLD)
GOCIFFF
Gulf of Carpentaria Inshore Fin Fish Fishery (QLD)
ONLF
Offshore Net and Line Fishery (NT)

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) In Queensland, under the Fisheries Act 1994 (Qld), Indigenous fishers are able to use prescribed traditional and non-commercial fishing apparatus in waters open to fishing. Size and bag limits and seasonal closures do not apply to Indigenous fishers. Further exemptions to fishery regulations can be obtained through permits.

Queensland – Recreational (including some charter and Indigenous fishers) Survey of Queensland residents only from August 2013 to October 2014 [Webley et al. 2015]

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Catch Chart

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

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References

  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. 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.
  5. 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.
  6. 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.
  7. Martell, S and R. Froese 2013, A simple method for estimating MSY from catch and resilience. Fish and Fisheries 14: 504–514
  8. 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.
  9. 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.
  10. Newman, SJ, Mitsopoulos, G, Skepper, C and Smith, E 2018, North Coast Nearshore and Estuarine Resource Status Report 2017. pp. 123–126. In: Gaughan, D.J. and Santoro, K. (eds.). Status Reports of the Fisheries and Aquatic Resources of Western Australia 2016/17: The State of the Fisheries. Department of Primary Industries and Regional Development, Western Australia, Perth, Australia. 237p.
  11. 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.
  12. 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.
  13. Queensland Department of Agriculture and Fisheries 2018, Queensland Stock Status Assessment Workshop Proceedings 2018. Species Summaries. 19–20 June 2018, Brisbane.
  14. Ryan, KL, Hall, NG, Lai, EK, Smallwood, CB, Taylor, SM and Wise, BS 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, Government of Western Australia, Perth. 
  15. 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.
  16. Webley, J, McInnes, K, Teixeira, D, Lawson, A and Quinn, R 2015, Statewide Recreational Fishing Survey 2013–14. Department of Agriculture and Fisheries, Brisbane.
  17. 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.
  18. 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.

Downloadable reports

Click the links below to view reports from other years for this fish.