Deepwater Flathead (2020)
Date Published: June 2021
Caught only in the Great Australian Bight, in Commonwealth waters, Deepwater Flathead is a sustainable stock.
Stock Status Overview
|Commonwealth||Great Australian Bight||Sustainable||Spawning stock biomass, fishing mortality|
The biological stock structure of Deepwater Flathead is unknown; however, it is treated as a single biological stock or management purposes in the Great Australian Bight Trawl Sector (GABTS) of the Southern and Eastern Scalefish and Shark Fishery (SESSF). A stock assessment has been completed for this biological stock [Tuck et al. 2019].
Here, assessment of stock status is presented at the biological stock level—Great Australian Bight.
Great Australian Bight
The most recent quantitative assessment [Tuck et al. 2019] estimated that the spawning biomass at the start of the 2018–19 fishing season was 37 per cent of the unfished (1978) level. This assessment was generally consistent with previous assessments [Haddon 2016] and fishery-independent surveys [Knuckey et al. 2009 and 2011], however the 2015 fishery-independent survey suggested a 45 per cent decrease in Deepwater Flathead catch rates compared to previous surveys [Knuckey et al. 2015]. There were uncertainties around the outputs of the survey due to seismic testing and unintentional changes to the trawl net used. The 2018 fishery-independent survey suggested a decrease in relative biomass of 33 per cent compared to 2015 and 63 per cent compared to 2011 [Knuckey et al. 2018]. This trend is concerning, though these changes may reflect movement of fish rather than changes in abundance.
Previous quantitative stock assessments estimated that the spawning biomass was progressively fished-down in the mid-2000s, but the biological stock had recovered to above the maximum economic yield target of 43 per cent of virgin biomass by the start of 2010, and was 44 per cent in 2016 [Klaer 2013, Haddon 2016]. The recovery was likely a result of lower fishing pressure, combined with at least one substantial recruitment event. As indicated above, the 2019 stock assessment suggests spawning biomass at the start of 2018–19 to be 37 per cent of the unexploited biomass. The quantitative assessment provided good fits to the catch rate, length and age data, but a poor fit for the last two years of fishery-independent trawl data [Tuck et al. 2019]. There is no evidence of a truncation in size or age structure of Deepwater Fathead [Haddon 2016]. The above evidence indicates that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired.
The recommended biological catch (RBC) estimated by Haddon  (1155t) was used to set a total allowable catch (TAC) for the SESSF Great Australian Bight Trawl Sector (Commonwealth) for the 2018–19 fishing season (1128t). Total landed catch of Deepwater Flathead in the 2019-20 fishing season was 693 t (528t for the 2018-19 fishing season) below the RBC. This 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
Deepwater Flathead biology [Kailola et al. 1993, Stokie and Krusic-Golub 2005, Stokie and Talman 2003]
|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|
Distribution of reported commercial catch of Deepwater Flathead
|Total allowable catch|
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.
Commercial catch of Deepwater Flathead — note confidential catch not shown
- Castillo-Jordan, C, Althaus, F, Burch, P, Thomson, R, 2018 SESSF catches and discards for TAC purposes, 2018 CSIRO, Hobart
- Haddon, 2016, Deepwater flathead (Platycephalus conatus) stock assessment using data to 2015/16, draft report, CSIRO Oceans and Atmosphere, Hobart.
- 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.
- 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.
- Knuckey, I, Koopman, M and Hudson, R 2009, Resource survey of the Great Australian Bight Trawl Fishery—2009, AFMA Project 2008/848, Report to the Australian Fisheries Management Authority, Canberra.
- 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.
- 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.
- Knuckey, I, Koopman, M and Hudson, R 2018, Resource Survey of the Great Australian Bight Trawl Sector – 2018. AFMA Project 2017/0807. Fishwell Consulting 39pp.
- Moore, A and Mobsby 2018, Great Australian Bight Trawl Sector, in H Patterson, Larcombe, J, Nicol, S and Curtotti, R (eds), 8, Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra.
- 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.
- Stokie, T and Talman, S 2003, Age estimation of Deepwater Flathead (Neoplatycephalus conatus), Report to the Australian Fisheries Management Authority, Canberra.
- 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.