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King Threadfin (2018)

Polydactylus macrochir

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

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Summary

King Threadfin is a sustainable species in WA, the NT and the east coast of QLD. It is susceptible to overfishing in the Gulf of Carpentaria, where it is classified as a depleting stock.

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Stock Status Overview

Stock status determination
Jurisdiction Stock Fisheries Stock status Indicators
Western Australia Western Australia KGBMF Sustainable Catch
KGBMF
Kimberley Gillnet and Barramundi Managed Fishery (WA)
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Stock Structure

King Threadfin have numerous populations across northern Australia that are separated by 10–100s km or by large, coastal geographical features [Moore et al. 2011, Welch et al. 2010]. With the exception of the Gulf of Carpentaria, there is a lack of information on the degree to which this separation indicates separate biological stocks, and on boundaries between possible stocks.

Here, assessment of stock status is presented at the jurisdictional level—Western Australia and Northern Territory; at the biological stock level—Gulf of Carpentaria (Queensland); and the management unit level—East coast (Queensland).

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Stock Status

Western Australia

King Threadfin is landed in the Kimberley Gillnet and Barramundi Managed Fishery (KGBMF) of Western Australia. The catch of King Threadfin in the KGBMF has been low and stable for the past four years (2014–17), ranging from 19–25 tonnes (t), with a mean annual catch of 21.9 t. The recent catches from 2014–2017 are well below the average of 74.5 t for the 10 year period from 2004–13. This is due to low effort levels in the fishery [Newman et al. 2018] following the removal of two fishing licences from the Broome coast area. The Broome coast area has been closed to commercial fishing since late 2013. This commercial closure in the principal landing area for King Threadfin catches, in association with their rapid growth rates, is likely to have substantially increased the spawning stock biomass of this species. King Threadfin are landed by recreational fishers (estimated catch ~7 t), and also by charter fishers but only in small quantities (< 0.5 t). The above evidence indicates the biomass of this stock is unlikely to be depleted and that the recruitment is unlikely to be impaired. Furthermore, the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired.

On the basis of the evidence provided above, King Threadfin in Western Australia is classified as a sustainable stock.

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Biology

King Threadfin biology [Welch et al. 2010]

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
King Threadfin 22 years, 1 600 mm TL  Males 2 years, 610 mm TL Females 6 years,1 000 mm TL
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Distributions

Distribution of reported commercial catch of King Threadfin
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Tables

Fishing methods
Western Australia
Commercial
Gillnet
Recreational
Hook and Line
Indigenous
Various
Management methods
Method Western Australia
Charter
Bag limits
Limited entry
Passenger restrictions
Spatial closures
Spatial zoning
Commercial
Gear restrictions
Limited entry
Spatial closures
Spatial zoning
Vessel restrictions
Recreational
Bag limits
Licence (Recreational Fishing from Boat License)
Spatial closures
Active vessels
Western Australia
4 in Charter, 4 in KGBMF
Charter
Tour Operator (WA)
KGBMF
Kimberley Gillnet and Barramundi Managed Fishery (WA)
Catch
Western Australia
Commercial 20.52t in KGBMF
Charter 0.05 t
Indigenous Unknown
Recreational 7.50 t ± 2.26 se
KGBMF
Kimberley Gillnet and Barramundi Managed Fishery (WA)

Western Australia – Recreational (Catch) Boat-based recreational catch is from 1 September 2015–31 August 2016. These data are derived from those reported in Ryan et al. 2017. It is important to note that catches of King Threadfin are underestimated as shore-based fishers were out of scope of the survey. Shore based catches of King Threadfin are not known.

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 Subject to the defence that applies under 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.

Queensland – Recreational (catch) Survey of Queensland residents only from August 2013–October 2014 [Webley et al 2015].

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.

Northern Territory – Indigenous (management methods) The Fisheries Act 1988 (NT), specifies that “…without derogating from any other law in force in the Territory, nothing in a provision of this Act or an instrument of a judicial or administrative character made under it limits the right of Aboriginals who have traditionally used the resources of an area of land or water in a traditional manner from continuing to use those resources in that area in that manner”.

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Catch Chart

Commercial catch of King Threadfin
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References

  1. Bayliss, P, Buckworth, R and Dichmont, C (Eds) 2014, Assessing the water needs of fisheries and ecological values in the Gulf of Carpentaria. Final Report prepared for the Queensland Department of Natural Resources and Mines (DNRM), CSIRO, Australia.
  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, Department of Primary Industries, Brisbane.
  3. DPIR 2018, Status of Key Northern Territory Fish Stocks Report 2016 Northern Territory Government. Department of Primary Industry and Fisheries. Fishery Report No. 119.
  4. Garrett, R 1992, Biological Investigation of King Salmon Polydactylus sheridani in the Gulf of Carpentaria: A Summary Report. In: Healy, T (ed) Gulf of Carpentaria Fishery Review Background Paper No. 1, QFMA, Brisbane.
  5. Halliday, I, Staunton-Smith, J, Robins, J, Mayer, D and Sellin, M 2007, Using age-structure of commercial catch to investigate the importance of freshwater flows in maintaining barramundi and king threadfin populations, in I Halliday and J Robins (eds) Environmental flows for sub-tropical estuaries: understanding the freshwater needs for sustainable fisheries production and assessing the impacts of water regulation, Department of Primary Industries and Fisheries, Brisbane, 92–106.
  6. Halliday, IA, Robins, JB, Mayer, DG, Staunton-Smith, J and Sellin, MJ 2008, Effects of freshwater flow on the year-class strength of a non-diadromous estuarine finfish, king threadfin (Polydactylus macrochir), in a dry-tropical estuary. Marine and Freshwater Research 59: 157–164.
  7. Moore, BR 2011, Movement, connectivity and population structure of a large, non-diadromous tropical estuarine teleost. PhD thesis, James Cook University.
  8. Moore, BR, Stapley, JM, Williams, AJ, Welch DJ, 2017. Overexploitation causes profound demographic changes to the protandrous hermaphrodite king threadfin (Polydactylus macrochir) in Queensland’s Gulf of Carpentaria, Australia. Fisheries Research, Volume 187, 199–208p.
  9. Moore, BR, Welch, DJ and Simpfendorfer, CA 2011, Spatial patterns in the demography of a large estuarine teleost: king threadfin, Polydactylus macrochir. Marine and Freshwater Research 62: 937–951.
  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, DJ 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. Queensland Department of Agriculture and Fisheries 2018, Queensland Stock Status Assessment Workshop Proceedings 2018. Species Summaries. 19–20 June 2018, Brisbane.
  12. Robins, JB, Halliday, IA, Staunton-Smith, J, Mayer, DG and Sellin, MJ 2005, Freshwater flow requirements of estuarine fisheries in tropical Australia: a review of the state of knowledge and application of a suggested approach, Marine and Freshwater Research, 56: 343–360.
  13. Ryan, KL, Hall, NG, Lai, EK, Smallwood, CB, Taylor, SM, 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. 
  14. Webley, J, McInnes, K, Teixeira, D, Lawson, A and Quinn, R 2015, Statewide Recreational Fishing Survey 2013–14. Department of Agriculture and Fisheries, Brisbane.
  15. Welch, D, Gribble, N and Garrett, R 2002, Assessment of the Threadfin Salmon Fishery in Queensland–2002. Department of Primary Industries, Brisbane.
  16. Welch, DJ, Ballagh, A, Newman, SJ, Lester, RJ, Moore, B, van Herwerden, L, Horne, J, Allsop, Q, Saunders, T, Stapley, J and Gribble, NA 2010, Defining the stock structure of northern Australia’s threadfin salmon species. Draft Final Report to the Fisheries Research and Development Corporation, Project 2007/032. Fishing and Fisheries Research Centre, James Cook University, Townsville, Australia.

Downloadable reports

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