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Deepwater Flathead (2023)

Platycephalus conatus

  • Andy Moore (Australian Bureau of Agricultural and Resource Economics and Sciences)

Date Published: June 2023

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Summary

Caught only in the Great Australian Bight, in Commonwealth waters, Deepwater Flathead is a sustainable stock.

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Stock Status Overview

Stock status determination
Jurisdiction Stock Stock status Indicators
Commonwealth Great Australian Bight Sustainable

Spawning stock biomass, fishing mortality, size and age structure, fishery independent survey

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Stock Structure

The biological stock structure of Deepwater Flathead is unknown; however, it is treated as a single biological stock for management purposes in the Great Australian Bight Trawl Sector (GABTS) of the Southern and Eastern Scalefish and Shark Fishery (SESSF).

Here, assessment of stock status is presented at the biological stock level—Great Australian Bight.

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Stock Status

Great Australian Bight

This stock is taken in the Great Australian Bight Trawl Sector (GABTS) of the Southern and Eastern Scalefish and Shark Fishery (SESSF) and stock status is assessed based on the outputs of the Commonwealth stock assessment.

The target reference point for Deepwater Flathead of 43 per cent of the unfished spawning stock biomass [Kompas et al. 2012] was derived from a bio-economic model of the fishery [AFMA 2011]. The 2019 tier 1 assessment [Tuck et al. 2019] estimated spawning biomass in 2018 to be 37% of the unfished (1978) level, and above the 20% of unfished limit reference point. Using the 20:35:43 harvest control rule, Tuck et al. [2019] produced a 3-year average recommended biological catch of 1,238 tonnes (t). 

The 2021–22 Deepwater Flathead Total Allowable Catch (TAC) was set at 1,238 t, which is the second year of a three-year TAC. The 2019 stock assessment suggested no change in depletion rate between 2013, 2016 and 2019 [Klaer 2013; Haddon 2016; Tuck et al. 2019], although the estimate of spawning stock biomass decreased to 4,083 t. The tier 1 assessment provided good fits to the catch rate, length and age data, but a poor fit for the fishery-independent trawl data [Tuck et al. 2019]. There is no evidence of a truncation in size or age structure of Deepwater Flathead [Tuck et al. 2019].

Fishery-independent surveys have been undertaken in the GAB since 2005. The estimated relative abundance has been fairly stable since 2015, though these estimates are between 43% and 63% lower than the 2011 estimate [Knuckey et al. 2011, 2015, 2018, 2021].

Commonwealth landed catch in the 2021–22 fishing season was 701 t [Moore et al. 2022], up from 621 t in 2020–21.  The weighted average of the previous 4 calendar years (2017 to 2020) was calculated and used to estimate discards of 1.9 t, with no state catches recorded [Althaus et al. 2021]. 

The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. Furthermore, the 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 Great Australian Bight biological stock is classified as a sustainable stock.

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Biology

Deepwater Flathead biology [Kailola et al. 1993; Stokie and Talman 2003; Stokie and Krusic-Golub 2005; Brown and Sivakumaran 2007]

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
Deepwater Flathead

Females 26 years, 820 mm TL Males 19 years, 590 mm TL

Females 5–6 years, 430 mm TL Males 4–5 years, 430 mm TL
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Distributions

Distribution of reported commercial catch of Deepwater Flathead

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Tables

Fishing methods
Commonwealth
Commercial
Danish Seine
Otter Trawl
Management methods
Method Commonwealth
Commercial
Gear restrictions
Limited entry
Spatial closures
Total allowable catch
Catch
Commonwealth
Commercial 714.65t
Indigenous Unknown
Recreational Unknown

Commonwealth – Commercial (Management Methods/Catch). Data provided for the Commonwealth align with the Commonwealth Southern and Eastern Scalefish and Shark Fishery for the 2021–22 financial year.

Commonwealth – Recreational. The Australian Government does not manage recreational fishing in Commonwealth waters. Recreational fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters, under its management regulations.

Commonwealth – Indigenous. The Australian Government does not manage non-commercial Indigenous fishing in Commonwealth waters, with the exception of the Torres Strait. In general, non-commercial Indigenous fishing in Commonwealth waters is managed by the state or territory immediately adjacent to those waters.

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Catch Chart

Commercial catch of Deepwater Flathead — note confidential catch not shown

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References

  1. AFMA 2011, Southern and Eastern Scalefish and Shark Fishery – Great Australian Bight Resource Assessment Group (GABRAG) meeting, 27–28 October 2011, Australian Fisheries Management Authority, Adelaide.
  2. Althaus, F, Sutton, C and Cannard, T 2022, Southern and Eastern Scalefish and Shark Fishery catches and discards for TAC purposes using data until 2021, Revised after the SESSFRAG data meeting, 23–24 August 2022, CSIRO, Australia.
  3. Brown, LP and Sivakumaran, KP 2007, Spawning and reproductive characteristics of Bight redfish and deepwater flathead in the Great Australian Bight Trawl Fishery. Final report to Fisheries Research and Development Corporation Project No. 2003/003. Primary Industries Research Victoria, Queenscliff.
  4. Castillo-Jordan, C, Althaus, F, Burch, P, Thomson, R, 2018 SESSF catches and discards for TAC purposes, 2018 CSIRO, Hobart.
  5. Haddon, M 2016, Deepwater flathead (Platycephalus conatus) stock assessment using data to 2015/16, draft report, CSIRO Oceans and Atmosphere, Hobart.
  6. Kailola, PJ, Williams, MJ, Stewart, PC, Reichelt, RE, McNee, A and Grieve, C 1993, Australian Fisheries Resources, Bureau of Resource Sciences and Fisheries Research and Development Corporation, Canberra.
  7. Klaer, N, 2013 Deepwater flathead (Neoplatycephalus conatus) stock assessment based on data up to 2012/13 in GN Tuck (ed), Stock assessment for the Southern and eastern Scxalefish and Shark Fishery 2013, part 1, CSIRO, Hobart.
  8. Knuckey, I, Koopman, M and Hudson, R 2011, Resource survey of the Great Australian Bight Trawl Fishery—2011, Report to the Australian Fisheries Management Authority, Canberra.
  9. Knuckey, I, Koopman, M and Hudson, R 2015, Resource Survey of the Great Australian Bight Trawl Sector—2015, Australian Fisheries Management Authority Project 2014/0809, Fishwell Consulting.
  10. Knuckey, I, Koopman, M and Hudson, R 2018, Resource Survey of the Great Australian Bight Trawl Sector – 2018. AFMA Project 2017/0807. Fishwell Consulting.
  11. Knuckey, I, Koopman, M and Hudson, R 2021, Resource survey of the Great Australian Bight Trawl Sector 2021, report to AFMA, Fishwell Consulting, Queenscliff, and Australian Fisheries Management Authority, Canberra.
  12. Kompas, T, Che, N, Chu, L and Klaer, N 2012, Transition to MEY goals for the Great Australian Bight Trawl Fishery, report to FRDC, Australian Centre for Biosecurity and Environmental Economics, Crawford School of Public Policy, Australian National University, Canberra.
  13. Moore, A, Keller, K, Tuynman, H, 2022, Great Australian Bight Trawl Sector, in Patterson, H, Bromhead, D, Galeano, D, Larcombe, J, Timmiss, T, Woodhams, J and Curtotti, R (eds), Fishery status reports 2022, Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra.
  14. Stokie, T and Krusic-Golub, K 2005, Age estimation of Bight Redfish and Deepwater Flathead in the Great Australian Bight Trawl Fishery, 2004–05, Australian Fisheries Management Authority, Canberra.
  15. Stokie, T and Talman, S 2003, Age estimation of Deepwater Flathead (Neoplatycephalus conatus), Report to the Australian Fisheries Management Authority, Canberra.
  16. Tuck, G, Day, J and Burch, P 2019, Deepwater flathead (Neoplatycephalus conatis) stock assessment based on data up to 2018/19, CSIRO Oceans and Atmosphere Flagship, Hobart.

Downloadable reports

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