Browsing by Subject "management procedures"

Now showing 1 - 4 of 4
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    The approach recently developed by the IWC Scientific Committee for taking formal account of the results of robustness trials, together with their relative plausibilities, in assessing risk when selecting between alternative candidate management procedures
    (2007) Butterworth, Doug S
    A particular raison d’etre for the management procedure (MP) approach for providing scientific recommendations on management measures such as TACs is that it takes formal account of scientific uncertainties in its assessment of risks (primarily to the resource, but also to the fishery). This is achieved by considering the results of simulation tests which project the resource forward under the MP’s TAC-setting algorithm, not only under a model seen to best reflect the resource’s dynamics, but also under other models consistent with alternative plausible explanations of the data available
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    Candidate management procedures for the South African hake resource: Draft objectives and testing methodology
    (2010) Rademeyer, Rebecca A; Butterworth, Doug S
    Though revised operational objectives should only be finalised through an iterative process as the results of simulation tests of Candidate Management Procedures (CMPs), and hence their trade-off implications, become available, this process merits initiation at the present time.
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    Further candidate management procedures projections for the South African hake resource
    (2014) Rademeyer, Rebecca A; Butterworth, Doug S
    This document reports further developments in the hake OMP revision process. First the requested 150 000t upper cap is placed on the TAC, and tunings to different average TACs over the next 10 years are contrasted, together with options for a prefixed TAC for the next two years. The option of a soft lower cap on the TAC of 125 000t is explored, linked to a metarule for overriding this if the overall abundance index for M. paradoxus falls below a specified threshold. While it seems more likely than not that the introduction of this soft lower cap would make for a more stable fishery, there remains an appreciable chance that it may necessitate larger TAC reductions, and to lower TAC levels, than would otherwise be the case. Options to reduce the “lag” effects between changes in resource trends and in the TAC are explored, but with little success; basing the control rule on abundance index averages over the last two rather than last three years leads to greater interannual TAC variability. Results for an initial exploration of robustness to decreases in carrying capacity (a possible effect of climate change) point to the importance of further development of metarules to override the constraint on the 5% maximum downward TAC adjustment.
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    Generic management procedures for data-poor fisheries: forecasting with few data
    (Oxford University Press, 2015) Geromont, Helena F; Butterworth, Doug S
    The majority of fish stocks worldwide are not managed quantitatively as they lack sufficient data, particularly a direct index of abundance, on which to base an assessment. Often these stocks are relatively “low value”, which renders dedicated scientific management too costly, and a generic solution is therefore desirable. A management procedure (MP) approach is suggested where simple harvest control rules are simulation tested to check robustness to uncertainties. The aim of this analysis is to test some very simple “off-the-shelf” MPs that could be applied to groups of data-poor stocks which share similar key characteristics in terms of status and demographic parameters. For this initial investigation, a selection of empirical MPs is simulation tested over a wide range of operating models (OMs) representing resources of medium productivity classified as severely depleted, to ascertain how well these different MPs perform. While the data-moderate MPs (based on an index of abundance) perform somewhat better than the data-limited ones (which lack such input) as would be expected, the latter nevertheless perform surprisingly well across wide ranges of uncertainty. These simple MPs could well provide the basis to develop candidate MPs to manage data-limited stocks, ensuring if not optimal, at least relatively stable sustainable future catches.