Browsing by Author "Itoh, Tomoyuki"

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    A check of operating model predictions from the viewpoint of the management procedure implementation in 2016
    (2016) Takahashi, Norio; Kurota, Hiroyuki; Sakai, Osamu; Itoh, Tomoyuki; Butterworth, Doug S
    Values of the core vessels’ longline CPUE and aerial survey (AS) indices (two required inputs to the Bali management procedure) are compared to projection results obtained from the operating model (OM). Recent observations for the CPUE index fall within the 95% probability envelope predicted by the Base case OM in 2011. The AS index values for 2012, 2014 and 2016, however, are outside the range predicted by this Base case. The 2016 AS index value remains outside the 95% probability envelope predicted even for the Robustness Test which assumes higher variability for the projected AS index, though the index values for 2012 and 2014 fall within this envelope. This constitutes a possible indication of Exceptional Circumstances. Through discussion of the Exceptional Circumstances reflected by the 2016 AS index, together with the other elements contributing to Exceptional Circumstances and consideration of their severities, the ESC needs to formulate management advice for the action required to calculate TAC for 2018-2020 fishing seasons. Regarding the TAC to be recommended for the 2017 season, we consider that no modification of the TAC value is required given that there has been no unexpected change in the fisheries indicators examined and there are no indications of any decline in recruitment indices for 2016.
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    A check of operating model predictions from the viewpoint of the management procedure implementation in 2017
    (2017) Takahashi, Norio; Sakai, Osamu; Kurota, Hiroyuki; Itoh, Tomoyuki; Butterworth, Doug S
    Values of the core vessels’ longline CPUE and aerial survey (AS) indices (two required inputs to the Bali management procedure) are compared to projection results obtained from the SBT operating model (OM). The most recent observations for the CPUE index and the AS index fall within the 95% probability envelopes predicted by the Base case OM in 2011. As regards a decision on implementation of the recommended TAC (calculated by the MP in 2016 for the 2018-2020 fishing seasons) for the 2018 season, it is considered that no modification of the value of this TAC is required because: 1) there is no evidence to support a declaration of Exceptional Circumstances from the viewpoints of a check of the OM predictions, this year’s in-depth stock assessment/projections, and other potential reasons (Indonesian small fish catch, overcatch of reported global TAC, unaccounted catch mortality); 2) no unexpected change has been detected in the fisheries’ indicators examined; and 3) there are no indications of any appreciable decline in recruitment indices for 2017.
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    A scientific alternative to moratoria for rebuilding depleted international tuna stocks
    (Wiley, 2015) Hillary, Richard M; Preece, Ann L; Davies, Campbell R; Kurota, Hiroyuki; Sakai, Osamu; Itoh, Tomoyuki; Parma, Ana M; Butterworth, Doug S; Ianelli, James; Branch, Trevor A
    There is considerable international concern and scientific debate about the current state and future of tuna stocks worldwide and the capacity of Regional Fisheries Management Organisations to manage the associated fisheries effectively. In some cases, this concern has extended to predictions of imminent collapse with minimal chances of recovery, even under a commercial catch moratorium. As a viable alternative to a full fishery closure, the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) has adopted a scientifically tested, adaptive rebuilding strategy for the depleted southern bluefin tuna (Thunnus maccoyii) stock. The management procedure (MP) adopted involves a harvest control rule that fully specifies the total allowable catch as a function of key indicators of stock status, adjusting future harvest levels every three years so as to meet the rebuilding targets agreed by CCSBT. It was chosen from a subset of candidate MPs selected following extensive simulation testing. This involved first selecting a wide range of plausible scenarios for stock status and input data, ranging from pessimistic to optimistic, against which the alternative candidate MPs were tested to ensure that they were robust to important uncertainties. This is the first time that a comprehensively evaluated MP has been adopted for an internationally managed tuna stock. Both the process and the outcomes have broad applicability to other internationallymanaged stocks.