Details of the latest assessment of southern bluefin tuna (SBT), including updated fishery indicators, are available from the report of the Twenty Seventh meeting of the CCSBT Scientific Committee:
A brief report on the Report on Biology, Stock Status and Management of Southern Bluefin Tuna is available at:
The next full stock assessment for southern bluefin tuna is scheduled to be conducted during 2023.
Summary of the Latest Assessment
The Twenty Fifth Meeting of the Scientific Committee noted from the 2020 full stock assessment that:
- The stock, as indicated by relative Total Reproductive Output (TRO), is estimated to be 20% (16-24%; 80% P.I.) of TRO0;
- The stock remained below the level estimated to produce maximum sustainable yield (MSY);
- Stock status has improved since the previous stock assessments conducted in 2017 which indicated that relative TRO was at 13% (11-17% 80% PI) of TRO0;
- The fishing mortality rate is below the level associated with MSY; and
- The stock has been rebuilding by approximately 5% per year since the low point in 2009.
The 2020 assessment also indicated that the stock has increased from a low of 10% of initial TRO in 2009.
Summary of indicators
The review of indicators by the Extended Scientific Committee in 2022 is summarised below:
- Compared to the previous year, the indicators are mixed (some increased, some decreased, and others were neutral); however, there were no unusual signals nor suggestions of any reasons for concern. Overall, the longer term trends in the indicators are consistent with the most recent assessment that indicated a resource that is expected to continue increasing.
- Two age-1 abundance indices are derived from the trolling survey. The TRG recruitment index shows a low level from the 2016 to 2021 cohort, and the TRP recruitment index recorded zero values in 2018 and 2019, suggesting some concern about potential low recruitment in recent years, although the TRP index increased in 2022.
- The Parent-Offspring-Pairs detections rate decreased for the latest year it was calculated (2018), which is consistent with an increase in population size.
- The gene-tagging age 2 abundance estimate for 2019 increased compared to the estimates for 2017 and 2018 (no estimate for 2020 is available this year due to the impact of COVID-19).
- The Japanese longline nominal CPUE for age 4+ increased in 2021 and was above the 10-year mean. In contrast, the new Japanese standardised CPUE series (GAM) for age 4+ decreased slightly. Both series indicate that CPUE has been increasing since 2007.
- The standardised CPUE for all ages from the New Zealand domestic longline fishery increased.
- The Korean standardised CPUE for all ages in Statistical Areas 8 and 9 showed an increasing trend since the mid-2000s.
- For the standardised Taiwanese CPUE for all ages, the trends remained similar to the past but increased in both areas (central-eastern and western) with updated data in 2021.
Annual Review of implementation of the CCSBT Management Procedure
Following a review of stock or fishery indicators, the Management Procedure input data, population dynamics, fishing, or fishing operations and the OMMP advice on the incorporation of the new CPUE series on performance of the Cape Town Procedure (CTP), the Extended Scientific Committee agreed:
- There was no need to modify the TAC for 2023;
- The CTP can be used to recommend the TAC for 2024-2026; and
- There is a need to consolidate the future operation of the Indonesian catch and biological monitoring program, resolve the current uncertainty in the length frequency distributions between the Catch Documentation Scheme and catch monitoring program, and undertake a more detailed assessment of the implications of the shift in fleet operations between CCSBT Statistical Area 1 and Statistical Area 2 over recent years and its potential implications for stock assessment.
The Extended Scientific Committee recommended that the global TAC in 2023 should remain at 17,647 t., and from operation of the CTP, the Extended Scientific Committee also recommended a global TAC of 20,647 t. for 2024-2026.
