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Southern Bluefin Tuna

Thunnus maccoyii

  • Heather Patterson (Australian Bureau of Agricultural and Resource Economics and Sciences)
  • Ilona Stobutzki (Australian Bureau of Agricultural and Resource Economics and Sciences)
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Stock Status Overview

Stock status determination
Jurisdiction Stock Fisheries Stock status Indicators
Commonwealth Global CCSBT, SBTF Overfished Spawning stock biomass, projections of rebuilding
CCSBT
Commission for the Conservation of Southern Bluefin Tuna (CTH)
SBTF
Southern Bluefin Tuna Fishery (CTH)
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Stock Structure

Southern Bluefin Tuna constitutes a single, highly migratory biological stock that spawns in the north-east Indian Ocean and migrates throughout the temperate southern oceans, supporting a number of international fisheries1.

Here, assessment of stock status is presented at the biological stock level—global.

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Stock Status

Global

The biological stock of Southern Bluefin Tuna is fished by Australian fishers endorsed to fish in the Southern Bluefin Tuna Fishery (Commonwealth) and numerous other international jurisdictions. The species is also caught by recreational fishers in the waters off southern Australia, and there are other sources of unaccounted mortalities, including catches by fleets that are not members of the Commission for the Conservation of Southern Bluefin Tuna (CCSBT)2,3. The total reported global catch peaked in the late 1950s at about 80 000 tonnes (t) before declining substantially; it has been relatively stable at about 12 000 t since the mid-2000s.

In 2011, the CCSBT adopted a management procedure (analogous to a harvest strategy, evaluated fully using management strategy evaluation) to guide the recovery of the biological stock to 20 per cent of unfished biomass by 2035 with 70 per cent probability. Performance of the management procedure is measured using the biomass of fish that are 10 years and older. Since 2012, the agreed management procedure has been used to determine the global total allowable catch, which was set at 14 647 t for 2015–17. In line with this, Australia’s total allowable catch for the 2014–15 fishing season was 5665 t, of which 5519 t was landed. The most recent assessment (2014) undertaken by the CCSBT takes into account reported catch from all international jurisdictions4. It also examines the sensitivity of the results to alternate estimates of unaccounted fishing mortalities. The current level of unaccounted fishing mortality from all sources is uncertain, but there are indications it may be substantial3.

By 2000, the stock was estimated to be overfished, and to have declined to a small fraction of the unfished biomass5. The most recent assessment estimated that the biomass of fish 10 years and older in the Southern Bluefin Tuna biological stock is still low, at six to nine per cent of unfished levels4. The most recent estimate of spawning stock biomass is 8–12 per cent of unfished levels4. Based on this evidence, the stock is considered to be recruitment overfished. There may be substantial unaccounted mortality of Southern Bluefin Tuna4. Projections of the performance of the management procedure under scenarios of different levels of unaccounted mortalities showed that these mortalities reduce the probability of rebuilding to the specified interim management target to below the required 70 per cent within the specified time frame4. Although there has been a slight improvement in the estimated biomass of fish 10 years and older since the last assessment in 20116, the biological stock remains recruitment overfished at a global scale, and is well below the interim target level adopted by the CCSBT2,3,4. The level of fishing pressure, particularly when accounting for the additional sources of mortality, may prevent the stock from recovering from its recruitment overfished state, in line with the management procedure.

On the basis of the evidence provided above, the global biological stock is classified as an overfished stock.

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Biology

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
Southern Bluefin Tuna 40+ years; ~1900 mm FL ~11–12 years; 1580–1630 mm FL

Southern Bluefin Tuna biology7–9

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Distributions

Distribution of reported commercial catch of Southern Bluefin Tuna

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Tables

Fishing methods
Commonwealth
Commercial
Pelagic Longline
Pole and Line
Trolling
Purse Seine
Various
Recreational
Spearfishing
Hand Line, Hand Reel or Powered Reels
Management methods
Method Commonwealth
Commercial
Area restrictions
Catch limits
Individual transferable quota
Recreational
Bag limits
Boat limits
Active vessels
Commonwealth
24, 442 in CCSBT
CCSBT
Commission for the Conservation of Southern Bluefin Tuna (CTH)
Catch
Commonwealth
Commercial 14.35Kt in CCSBT, 5.52Kt in SBTF
Indigenous Unknown
Recreational Tasmania (2007–08): 14 t (~1.8  per cent error), South Australia (2013–14): 150.78 t (47 per cent error), Victoria (2011): 240 t (31 per cent error), Tasmania (2011–12): 75.8 t (error not available), Victoria (2007–08): 29.1 t (error not available)
CCSBT
Commission for the Conservation of Southern Bluefin Tuna (CTH)
SBTF
Southern Bluefin Tuna Fishery (CTH)

Recreationala,b Indigenousc Catchd

a 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. Recreational catches reported here are from state surveys during specific time periods, as noted.

b Recreational and Indigenous fishing sectors reported here are New South Wales, Queensland, South Australia, Tasmania, Victoria and Western Australia. A tick indicates that a measure exists in at least one of these jurisdictions.

c 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.

d Catches reported for the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) are for 2014, the most recent year available.

e Victoria – Recreational (catch) Unpublished data.

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Catch Chart

Commercial catch of Southern Bluefin Tuna

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Effects of fishing on the marine environment

  • Southern Bluefin Tuna was listed as conservation dependent under the Environment Protection and Biodiversity Conservation Act 1999 in 2010.
  • An ecological risk assessment on non-target species in the Australian purse-seine fishery (which caught approximately 90 per cent of Australia’s Southern Bluefin Tuna allocation in the 2014–15 fishing season) found that the risk to the sustainability of non-target species was low14.
  • Australia implements regulations to minimise the environmental impact of fisheries for tuna and tuna-like species on pelagic ecosystems, specifically on seabirds, sea turtles and sharks15,16.
  • Australia has prohibited the practice of shark finning and the use of wire leaders in longline fisheries managed by the Commonwealth, to reduce fishery impacts on sharks15,16.
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Environmental effects on Southern Bluefin Tuna

  • Interannual variation in abundance of Southern Bluefin Tuna in the Great Australian Bight is well documented. Habitat preference models for the Great Australian Bight have been developed using sea surface temperature and chlorophyll data17. These models can predict regions of the Great Australian Bight and Australian south-east coast where the relative abundance of Southern Bluefin Tuna is expected to be the highest.
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References

  1. 1 Proctor, CH, Thresher, RE, Gunn, JS, Mills, DJ, Harrowfield, IR and Sie, SH 1995, Stock structure of the Southern Bluefin Tuna, Thunnus maccoyii: an investigation based on probe micro analysis of otolith composition, Marine Biology, 122(4): 511–526.
  2. 2 Commission for the Conservation of Southern Bluefin Tuna 2015, Report of the twentieth meeting of the Scientific Committee, Incheon, South Korea, 1–5 September 2015.
  3. 3 Patterson, H, Stobutzki, I and Curtotti, R 2016, Southern Bluefin Tuna Fishery, in H Patterson, R Noriega, L Georgeson, I Stobutzki and R Curtotti (eds), Fishery status reports 2016, Australian Bureau of Agricultural and Resource Economics and Sciences, Canberra, 391–403.
  4. 4 Commission for the Conservation of Southern Bluefin Tuna 2014, Report of the nineteenth meeting of the Scientific Committee, Auckland, New Zealand, 1–6 September 2014.
  5. 5 Commission for the Conservation of Southern Bluefin Tuna 2005, Report of the sixth meeting of the Stock Assessment Group, 29 August–3 September 2005, Taipei, Taiwan.
  6. 6 Commission for the Conservation of Southern Bluefin Tuna 2011, Report of the sixteenth meeting of the Scientific Committee, Bali, Indonesia, 19–28 July 2011.
  7. 7 Davis, T, Farley, J and Gunn, J 2001, Size and age at 50% maturity in SBT: an integrated view from published information and new data from the spawning ground, CCSBT-SC/0108/16, Tokyo, Japan, 28–31 August 2001.
  8. 8 Gomon, M, Bray, D and Kuiter, R 2008, Fishes of Australia’s south coast, New Holland Publishers, Sydney.
  9. 9 Laslett, GM, Eveson, JP and Polacheck, T 2002, A flexible maximum likelihood approach for fitting growth curves to tag-recapture data, Canadian Journal of Fisheries and Aquatic Sciences, 59: 976–986.
  10. 10 Forbes, E, Tracey, S and Lyle, L 2009, Assessment of the 2008 recreational gamefish fishery of southeast Tasmania with particular reference to Southern Bluefin Tuna, Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, Hobart.
  11. 11 Green, C, Brown, P, Giri, K, Bell, J and Conron, S 2012, Quantifying the recreational catch of southern bluefin tuna off the Victorian coast, Recreational Fishing Grant Program Research Report, Department of Primary Industries, Victoria.
  12. 12 Tracey, S, Lyle, JM, Ewing, G, Hartmann, K and Mapleston, A 2013, Offshore recreational fishing in Tasmania 2011/12, Institute of Marine and Antarctic Studies, University of Tasmania, Hobart.
  13. 13 Giri, K and Hall, K 2015, South Australian recreational fishing survey 2013–14, Fisheries Victoria Internal Report Series No. 62, Victoria.
  14. 14 Zhou, S, Fuller, M and Smith, T 2009, Rapid quantitative risk assessment for fish species in seven Commonwealth fisheries, report for the Australian Fisheries Management Authority, Canberra.
  15. 15 Australian Fisheries Management Authority 2016, Eastern Tuna and Billfish Fishery Management Arrangements Booklet: 2016 Fishing Season, AFMA, Canberra.
  16. 16 Australian Fisheries Management Authority 2016, Western Tuna and Billfish Fishery Managements Arrangements Booklet: 2016 Fishing Season, AFMA, Canberra.
  17. 17 Eveson, JP, Hobday, AJ, Hartog, JR, Spillman, CM and Rough, K 2014, Forecasting spatial distribution of Southern Bluefin Tuna habitat in the Great Australian Bight, FRDC Project No. 2012/239, CSIRO Oceans and Atmosphere Flagship, Hobart.

Archived reports

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