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King Threadfin in the WA and NT jurisdictions, as well as four of the five QLD east coast stocks are classified as sustainable. In contrast, the Gulf of Carpentaria biological stock is classified as a depleted stock. Due to lack of reliable indicators the Far North East Coast stock is undefined.

King Threadfin have numerous populations across northern Australia that are separated by 10 to 100s km or by large, coastal geographical features [Moore et al. 2011; Welch et al. 2010]. Apart from 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. The Queensland stock assessment of King Threadfin was conducted based on six assessment regions; five on the east coast plus one in the Gulf of Carpentaria [Leigh et al. 2021], here they are considered the best approximation of biological stock. 

This assessment of stock status is presented at the jurisdictional level—Western Australia and Northern Territory; and at the biological stock level— Far North East Coast, North East Coast, Mackay East Coast, Central East Coast, South East Coast and Gulf of Carpentaria (Queensland). 

Western Australia

King Threadfin is one of the indicator species [Newman et al. 2018] for the North Coast Nearshore and Estuarine Resource (NCNER) and as such the stock status of King Threadfin contributes to determining the risk-level for the sustainability of the suite of species available for harvest in the NCNER. King Threadfin is currently only landed by the Kimberley Gillnet and Barramundi Managed Fishery (KGBMF). There is currently no formal harvest strategy for King Threadfin, but catches are evaluated against a period of stable catches from 2004–13, which averaged 74.5 t. This assessment of King Threadfin is supported by predictions for biomass and harvest rate from a data-limited Catch-MSY assessment model, with catches compared periodically to a model prediction for maximum sustainable yield (MSY).

In 2022, the commercial King Threadfin catch within the KGBMF of 13.3 t, was well below the average catch of the 2004–13 period and over the past 10 years, catches have been well below the average catch for the period from 2004–13. In recent years, overall commercial effort directed towards this species (and annual catches) have declined, in part due to two commercial gillnet licenses being removed in 2013 from the Broome coast area of the fishery [Trinnie et al. 2023], along with closures to commercial fishing along the Pilbara coast and Eighty-mile beach in the mid-2000s. This large area of the fishery is now only exposed to recreational, charter and indigenous fishing.

Catch levels of King Threadfin across the NCNER over the last 10 years (2013–22) ranged from 11.7–54.8 t, with a mean annual catch of 26.9 t. This is therefore much less than the average catch recorded for the previous 10 years (95.4 t). King Threadfin are mostly caught by commercial fishing, with the recreational and charter components of the total catch averaging approximately 21% in past 10 years. The Catch-MSY model applied to data on annual catches for this species since 1976, indicate that annual catches increased steadily until the mid-1990s, and then exceeded the upper 95% confidence intervals for this MSY prediction from 1997–2004. Since the mid-2000s however, catches have remained at or well below the mean MSY prediction. The trend of catches being higher relative to MSY is also consistent with the predicted values for biomass falling below the limit reference point (0.5BMSY) for several years, before increasing to around BMSY in recent years, and recent fishing mortality remaining well below FMSY. However, it is important to recognise that Catch-MSY is a data-limited technique with relatively strong assumptions, dependent on user inputs. For this assessment, these included specified ranges for initial depletion (0.5–0.975, based on assumed catches pre-1976), final depletion (0.15–0.7, calculated by the program based on recent catches relative to maximum recorded annual catch) and medium resilience (r=0.3–0.8, noting this species has a longevity of approximately 10 years in WA). The above evidence indicates that the current biomass of this stock is unlikely to be depleted and that current level of fishing mortality is unlikely to be sufficiently high to cause the stock to become recruitment overfished. 

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

King Threadfin biology [Welch et al. 2010]

Distribution of reported commercial catch of King Threadfin - note confidential catch not shown.

Western Australia – Recreational (Catch). Boat-based recreational catch is from 1 September 2020–31 August 2021. These data are derived from those reported in Ryan et al. [2022]. 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 (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.

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

Queensland – Commercial (Management Methods). Harvest strategies are available at: https://www.daf.qld.gov.au/business-priorities/fisheries/sustainable/harvest-strategy   

Queensland – Commercial (Catch). Queensland commercial and charter data has 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.

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: “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.”

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

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