Greenback Flounder (2020)
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Greenback Flounder occur around Australia's southern coastline (including TAS), from Jervis Bay in NSW to Mandurah in WA. The species is also found in New Zealand. While there is evidence of population structuring in TAS Greenback Flounder, biological stock structure on the mainland coast in unknown, and assessments are consequently presented here at the jurisdictional level. Greenback Flounder are classified as negligible in WA, sustainable in VIC, undefined in TAS, and depleted in SA.
Photo: CSIRO Australian National Fish Collection
Stock Status Overview
|South Australia||South Australia||Depleted||
Catch, targeted effort
Greenback Flounder has a wide distribution in Australia, from Jervis Bay on the central coast of New South Wales, around the south of the continent including Tasmania, and up to Mandurah on the south-eastern coast of Western Australia [Kailola et al. 1993]. They also occur in New Zealand [Sutton et al. 2010].
The broad distribution of Greenback Flounder in Australia is thought to be divisible into a number of separate biological stocks. Genetic studies have demonstrated that the most significant division occurs between Australian and New Zealand populations [van den Enden et al. 2000]. Within Australia, there is strong evidence that populations in western Tasmania are genetically isolated from populations in Victoria, and northern and south-eastern Tasmania. These results are consistent with those of Kurth , who identified distinct western and eastern Tasmania populations on the basis of morphometrics. Biological stock structure along the southern mainland coasts of Australia is not known.
Here, assessment of stock status for Greenback Flounder is presented at the jurisdictional level—Western Australia, Victoria, Tasmania and South Australia.
The Lakes and Coorong Fishery (LCF) has traditionally been the most productive of South Australia's fisheries for Greenback Flounder, consistently accounting for > 95 per cent of the State's commercial catch since the 1970s [Earl and Ye 2016]. Small catches of this species are also taken by the Marine Scalefish Fishery (MSF) in some years. The most recent assessment for Greenback Flounder in the LCF was completed in 2020, and used a weight-of-evidence approach that considered fishery catch and effort data to the end of June 2019 [Earl 2020].
The primary measures of biomass and fishing mortality are total catch and total targeted effort from LCF gillnet fishers. Long-term trends in commercial catches indicate high interannual variability in fishable biomass in the Coorong estuary [Earl and Ye 2016]. Annual catches were highly variable and ranged from 3–65 tonnes (t).yr-1 during the 1980s and 1990s, before declining to historically low levels during the Millennium Drought from 2002 to 2010. In 2011–12, (i.e. the year after drought-breaking Murray River flows reached the Coorong estuary), a large biomass of large Greenback Flounder moved into the estuary from the adjacent marine environment [Earl et al. 2017], and catch sharply increased to 31 t. This sudden increase in biomass was not consistent with a spawning biomass that was in a recruitment overfished state [Earl and Ye 2016]. Low targeted fishing effort and low catches in recent years have been associated with low-moderate freshwater inflows and likely reflect a low fishable biomass in the Coorong estuary.
The high inter-annual variation in Greenback Flounder abundance in the Coorong estuary has been strongly associated with variation in freshwater inflow to the estuary, with a lag of 1–2 years [Earl and Ye 2016]. This is because large areas of estuarine habitat that support high abundances of this species are only available after years of high freshwater inflow (e.g. 1990–91, 1996–97, 2010–11). Alternatively, during periods of low inflow (e.g. from the Millennium Drought), abundance in the estuary is typically very low. It is likely that low flow conditions reduce the favourable habitat for Greenback Flounder in the estuary, during which time, some individuals move from the estuary to the ocean where they remain and can possibly return when estuarine conditions improve [Earl et al. 2017]. This was evidenced by the movement of a large biomass of Greenback Flounder into the estuary in 2011–12, after the most recent high inflow event, as indicated by trends in catch [Earl and Ye 2016]. The current low biomass in the Coorong estuary appears to relate to the below average freshwater inflow to the system in recent years, rather than a depleted spawning stock biomass (i.e. the spawning biomass is not considered to be recruitment overfished). The state-wide recreational catch of Greenback Flounder was estimated at 0.27 t in 2013–14 [Giri and Hall 2015].
Low targeted effort and catches since 2012–13 likely reflect low fishable biomass in the Coorong estuary as a consequence of low recruitment over several recent years due to the low freshwater inflows to the estuary (i.e. non-fishing effects). The above evidence indicates that the biomass of this stock is likely to be depleted and recruitment is likely to be impaired. Furthermore, the evidence indicates that current fishing mortality is constrained by management to a level that should allow the stock to recover from its recruitment impaired state.
On this basis, Greenback Flounder in South Australia is classified as a depleted stock.
[Sutton et al. 2010; Earl 2014]
|Species||Longevity / Maximum Size||Maturity (50 per cent)|
10 years; 500 mm TL
198 mm TL for females; 211 mm TL for males (SA)
Distribution of reported commercial catch of Greenback Flounder.
|Hook and Line|
|Hand held- Implements|
|Hook and Line|
|Hand held- Implements|
|Total allowable effort|
|Bag and boat limits|
|Bag and boat limits|
|Recreational||0.27 t (in 2013–14)|
Victoria – Indigenous (Management Methods) A person who identifies as Aboriginal or Torres Strait Islander is exempt from the need to obtain a Victorian recreational fishing licence, provided they comply with all other rules that apply to recreational fishers, including rules on equipment, catch limits, size limits and restricted areas. Traditional (non-commercial) fishing activities that are carried out by members of a traditional owner group entity under an agreement pursuant to Victoria’s Traditional Owner Settlement Act 2010 are also exempt from the need to hold a recreational fishing licence, subject to any conditions outlined in the agreement. Native title holders are also exempt from the need to obtain a recreational fishing licence under the provisions of the Commonwealth’s Native Title Act 1993.
- Conron S, Green C, Hamer P, Giri K and Hall K (2016). Corner Inlet-Nooramunga Fishery Assessment 2016. Fisheries Victoria Science Report Series No. 11.
- Earl, J 2014, Population biology and ecology of the greenback flounder (Rhombosolea tapirina) in the Coorong estuary, South Australia, PhD Thesis. School of Biological Sciences, Flinders University, Adelaide, Australia.
- Earl, J 2020, Assessment of the South Australian Lakes and Coorong Fishery in 2018/19. Report to PIRSA Fisheries and Aquaculture. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. SARDI Publication No. F2020/000208-01. SARDI Research Report Series No. 1059. 81pp.
- Earl, J and Ye, Q 2016, Greenback Flounder (Rhombosolea tapirina) Stock Assessment Report 2014/15. Report to PIRSA Fisheries and Aquaculture. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. SARDI Publication No. F2007/000315-2. SARDI Research Report Series No. 889. 40pp.
- Earl, J, Fowler, AJ, Ye, Q and Dittmann, S 2017, Complex movement patterns of greenback flounder (Rhombosolea tapirina) in the Murray River estuary and Coorong, Australia. Journal of Sea Research 122, 1-10.
- Giri, K, Hall, K 2015, South Australian Recreational Fishing Survey. Fisheries Victoria Internal Report Series No. 62.
- Kailola, PJ, Williams, MJ, Stewart, PC, Reichelt, RE, McNee, A and Grieve, C 1993, Australian fisheries resources, Bureau of Resource Sciences, Department of Primary Industries and Energy and Fisheries Research and Development Corporation, Canberra.
- Krueck N, Hartmann, K and Lyle J 2020, Tasmanian Scalefish Fishery Assessment 2018/19. Institute for Marine and Antarctic Studies, University of Tasmania.
- Kurth, D 1957, An investigation of the greenback flounder, Rhombosolea tapirina Günther. PhD thesis Thesis, University of Tasmania, Hobart.
- Lyle, JM, Stark, KE, Ewing, GP and Tracey, SR 2019, 2017-18 Survey of recreational fishing in Tasmania. Institute for Marine and Antarctic Studies, Hobart, Tasmania.
- Sutton, CP, MacGibbon, DJ, Stevens, DW 2010, Age and growth of greenback flounder (Rhombosolea tapirina) from southern New Zealand. New Zealand Fisheries Assessment Report 2010/48. Ministry of Fisheries, Wellington. 16pp.
- van den Enden, T, White, RW and Elliott, NG 2000, Genetic variation in the greenback flounder Rhombosolea tapirina Günther (Teleostei, Pleuronectidae) and the implications for aquaculture. Marine and Freshwater Research 51(1), 23-33.
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