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Latest Stock Assessment
Details of the latest full stock assessment of southern bluefin tuna, including updated fishery indicators, are available from the report of the Nineteenth meeting of the CCSBT Scientific Committee:
An update of the stock status is provided in the report of the Twentieth 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 will be conducted during 2017.
Summary of the Latest Assessment
The 2014 assessment suggested that the SBT spawning biomass is at a very low fraction (9%) of its original biomass as well as below the level that could produce maximum sustainable yield. However, there has been some improvement since the 2011 stock assessment. The current TAC has been set using the management procedure adopted in 2011, which has a 70% probability of rebuilding to the interim target biomass level by 2035.
Summary of indicators
There were mixed signals from the indicators in 2015. The overall results can be summarised as follows:
- No new information on recruitment was collected in 2015. The aerial survey, SAPUE and trolling surveys all ceased in 2015. The indicators information on recruitment from 2014 is unchanged.
- Longline CPUE indices for the Japanese fleet for age 5 to 7 are well above the historically lowest levels observed in the mid-2000s. The index for age 5 shows somewhat decreasing trends in recent years. The CPUE index for ages 8-11 have increased gradually in the most recent four years. The index for age 12+ decreased from 2008 to 2011 and has fluctuated around at a low level after that. Where areas overlapped, Korean CPUE trends were in reasonable agreement with those of Japan.
- Monitoring of length and age of Indonesian catches on the spawning ground indicate a substantial shift towards smaller and younger size and age classes since 2012. Information presented to the meeting indicates that the unusually small size classes have been caught off the spawning ground (areas 2 and 8) and that these fish should be excluded from the monitoring series. Therefore these is no updated trend on the spawning ground indicators at this meeting.
Sensitivity analysis around all sources of unaccounted catch mortality
The 2014 assessment included sensitivity analysis around all sources of unaccounted catch mortality. The Extended Scientific Committee (ESC) noted that it appears that significant levels of unaccounted mortality may have occurred which were not considered in the design of the Management Procedure (MP) and that if these levels are indeed true, they would amount to exceptional circumstances because the probability of rebuilding under the MP will be well below what was intended by the Extended Commission (EC).
The ESC also noted that continuing to follow the MP as proposed does lead to continued rebuilding in the short term even if the circumstances of the hypothesised additional unaccounted mortality are true. Hence, the ESC advised the EC to continue to follow the MP as formulated but, as a matter of urgency, to take steps to quantify all sources of unaccounted SBT mortality. If substantial levels of unaccounted mortality are confirmed, the ESC noted that there will be a need to retune the MP to achieve the EC’s stated rebuilding objective. In addition, the ESC advised that the EC take steps to ensure adherence to its TACs.