Browsing by Subject "Management Procedure"

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    A commentary on:salvaged pearls:lessons learned from a floundering attempt to develop a management procedure for Southern Bluefin Tuna
    (Elsevier, 2008) Butterworth, Doug S
    Kolody et al. (this issue, hereafter referred to as KPBD), in arguing lessons learnt from the process of attempting to develop a Management Procedure (MP) for Southern Bluefin Tuna (SBT: Thunnus maccoyi) in the Commission for Conservation of Southern Bluefin Tuna (CCSBT), put forward some possibly controversial views and interpretations. Given this, as a participant throughout that same process, I have been afforded the opportunity by Fisheries Research to offer my comments. The nature of this request is such as seeks an emphasis on points of difference, and what follows duly focuses primarily on these. Nevertheless, there is much in this valuable and thought-provoking contribution with which I fully agree, and my criticisms should be seen in the main as seeking to encourage further exchanges on these aspects of the MP approach to fisheries management, which I consider to have considerable merit
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    Does selectivity matter? A fisheries management perspective
    (Elsevier, 2014) Butterworth, Doug S; Rademeyer, Rebecca A; Brandão, Anabela; Geromont, Helena F; Johnston, Susan J
    The authors’ experiences in relation to the estimation of selectivity and its impact on the formulation of management advice are summarised for 14 different resources. These include instances where advice (generally in the form of a catch limit) is based on an assessment, as well as cases where a Management Procedure is developed (applying MSE) for this purpose. Relative paucity of older fish in either or both of catches or surveys is a frequent occurrence which has a number of alternative explanations, including doming in selectivity, and estimates of many biological reference points are not robustto this uncertainty. However, when the impacts of uncertainties in estimating selectivities are considered relative to those of the other uncertainties which also influence the calculation of catch limits, the former usually (although not always) seem to be of somewhat lesser importance.
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    A spatial multi-species operating model of the Antarctic Peninsula krill fishery and its impacts on land-breeding predators
    (2007) Plagányi, Éva E; Butterworth, Doug S
    The west coast rock lobster assessment of 20061 based on data to 2004 is updated to include data up to 2008. Over the last four years the exploitable biomass trend is upwards for Areas 7 and 8 and the resource as a whole, but downwards for Areas 5+6 and almost level for Areas 1+2 and 3+4. The overall increase since 2006 is significant at the 5% level. While better than median projections at the time the current OMP developed, the increase remains within the 95% probability intervals calculated at the time. An updated version of the Spatial Multi-species Operating Model (SMOM) of krillpredator-fishery dynamics is described. This has been developed in response to requests for scientific advice regarding the subdivision of the precautionary catch limit for krill among 15 small-scale management units (SSMUs) in the Scotia Sea, to reduce the potential impact of fishing on land-based predators. 2. The numerous uncertainties regarding the appropriate choice of parameter values in multi-species models is a major impediment. A pragmatic method proposed involves use of an operating model comprising alternative combinations that essentially try to bound the uncertainty in, for example, the choice of survival rate estimates as well as the functional relationships between predators and prey. 3. The operating model is assumed to simulate the “true” dynamics of the resource and is used to test decision rules for adjusting fishing activities (e.g. catch limits) based on field data forthcoming in the future. 4. An illustrative Management Procedure (MP) that includes a feedback structure is shown to perform better in terms of low risk to predators within each SSMU, than an approach lacking the ability to react and self-correct. 5. This modeling framework provides an example of a method for bounding some of the uncertainty associated with multi-species models used for management. Results are presented as probability envelopes rather than in point estimate form, giving a truer reflection of the uncertainty inherent in outcomes predicted on the basis of multi-species models, as well as highlighting how such probability envelopes could be narrowed given improved data on key parameters such as survival. Results are useful for evaluating the relative merits of different spatial allocations of krill catches. An example is given of 2 how such a framework can be used to develop a management scheme which includes feedback through management control rules.