*

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). 

Northern Territory

Knowledge of the genetic stock structure of King Threadfin in Northern Territory (NT) waters is limited. Welch et al. [2010] detected two different stocks in the NT from two locations sampled (i.e. Chambers Bay and Blue Mud Bay). Finer-scale sampling conducted in Queensland and Western Australia revealed stocks separated by distances of tens to hundreds of kilometres or by large, coastal geographical features [Welch et al. 2010; Moore et al. 2011]. The existence of multiple biological stocks in these states suggests that the stock structure of King Threadfin in the NT is likely to be more complex than currently described. 

In addition to genetic traits, the year class strength (i.e. productivity) of King Threadfin is affected by freshwater flow and coastal rainfall [Halliday et al. 2008]. Therefore, differences in these environmental drivers between adjacent catchments (as is evident in the NT; BOM 2020) may over-ride genotypic differences in productivity between neighbouring stocks.

Given uncertainties regarding the actual number of biological stocks of King Threadfin in NT waters, and current management arrangements for this species [as a single management unit], the assessment presented here was undertaken at the jurisdictional level.

The most recent assessment of King Threadfin in the Northern Territory (using data to the conclusion of 2019) indicated that the stock was impacted by high fishing pressure in the late 1970s and early 1980s, falling to 47% of the unfished (1950) biomass [Grubert and Saunders, unpublished]. However, there has been a strong recovery since that time, with the annual biomass as a proportion of virgin biomass exceeding 60% for the last two decades, reaching 98% by the end of 2019. In addition, commercial fishing effort and catches have declined significantly in recent years. During the decade from 2001–10, annual catches averaged 323 t. In 2022 (the most recent year of available data), catches were 129 t. The above evidence indicates that the biomass of the stock is unlikely to be depleted and that recruitment is unlikely to be impaired.

The contemporary (2019) fishing mortality rate, as a proportion of fishing mortality at maximum sustainable yield (MSY), was estimated at 16%, roughly one sixth of the rate required to achieve MSY [Grubert and Saunders unpublished]. The standardised catch per unit effort (CPUE) in 2019 was also at a historical high, following a significant increase in this indicator over the last decade (noting that this trend may in part be driven by an increase in targeting of King Threadfin). The above evidence indicates that the current level of fishing pressure is unlikely to cause the stock to become recruitment impaired.

On the basis of the evidence provided above, King Threadfin in the Northern Territory 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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