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Greenback Flounder (2020)

Rhombosolea tapirina

  • Jason Earl (South Australian Research and Development Institute)
  • Rodney Duffy (Department of Primary Industries and Regional Development, Western Australia)
  • Victorian Fisheries Authority (Victorian Fisheries Authority)
  • Nils Krueck (Institute for Marine and Antarctic Studies, University of Tasmania)

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Summary

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

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Stock Status Overview

Stock status determination
Jurisdiction Stock Stock status Indicators
Victoria Victoria Sustainable

Catch, CPUE

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Stock Structure

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 [1957], 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.

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Stock Status

Victoria

Commercial catches of Greenback Flounder in Victoria have averaged 11 t annually over the past two decades, and ranged between approximately 9–14 t accounting for 73 per cent of the national commercial catch over the past five years. 

Greenback Flounder are mostly taken commercially by haul seine and mesh net from Corner Inlet. Haul seine catch rates have shown an increasing trend in the standardised curve since a trough in the early 1990s, but have been highly variable over time with peaks in the raw data in 1978–79, 1984–85, 1997–98, 2004–05 and 2011–12 [Conron et al. 2016]. In contrast, the trend for mesh net catch-per-unit-effort (CPUE) follows a consistently negative trajectory which levelled out close to zero after the mid-2000s [Conron et al. 2020]. This produces a conflicting impression about stock status, but the mesh net results have much higher uncertainty and hence are considered less reliable. This is because of a past history of commercial operators targeting Greenback Flounder, likely with specifically designed mesh nets (loosely slung with small drop), whereas in recent years, fishers in Corner Inlet have predominantly targeted rock flathead and taken flounder as by-product. Consequently, the low landings of flounder by mesh net during the past two decades should not be interpreted as a reduction in biomass [Conron et al. 2020].  

The increasing trend in haul seine CPUE slowed asymptotically from the mid-2000s reaching its zenith in 2018–19. It is unclear if it has now stabilised, currently at 1.5 times the long-term average (1986–2015) or is at the top of a cycle that will show a decreasing pattern over the next two decades like it did from the late 1970s to early 1990s. Although the CPUE trends from the two different types of nets would indicate an undefined classification if the assumption that CPUE was reflecting biomass in each instance, the uncertainty in this assumption for mesh net CPUE supports exclusive reliance on haul seine CPUE as an indicator of biomass for Greenback Flounder in Victoria. 

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 provide above, Greenback Flounder in Victoria is classified as a sustainable stock.

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Biology

[Sutton et al. 2010; Earl 2014]

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
Greenback Flounder

10 years; 500 mm TL

198 mm TL for females; 211 mm TL for males (SA)

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Distributions

Distribution of reported commercial catch of Greenback Flounder.

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Tables

Fishing methods
Victoria
Commercial
Net
Recreational
Hook and Line
Hand held- Implements
Management methods
Method Victoria
Commercial
Gear restrictions
Limited entry
Size limit
Spatial closures
Temporal closures
Recreational
Bag limits
Gear restrictions
Size limit
Spatial closures
Catch
Victoria
Commercial 11.02t
Indigenous Unknown
Recreational Unknown

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.

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Catch Chart

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References

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. Giri, K, Hall, K 2015, South Australian Recreational Fishing Survey. Fisheries Victoria Internal Report Series No. 62.
  7. 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.
  8. Krueck N, Hartmann, K and Lyle J 2020, Tasmanian Scalefish Fishery Assessment 2018/19. Institute for Marine and Antarctic Studies, University of Tasmania.
  9. Kurth, D 1957, An investigation of the greenback flounder, Rhombosolea tapirina Günther. PhD thesis Thesis, University of Tasmania, Hobart.
  10. 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.
  11. 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.
  12. 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.

Downloadable reports

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