Browsing by Subject "Uncertainty"

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    A Bayesian state-space model for mixed-stock migrations, with application to Northeast Atlantic mackerel Scomber scombrus
    (National Inquiry Services Centre (NISC), 2007) Cunningham, Carryn L; Reid, D G; McAllister, M K; Kirkwood, G P; Darby, C D
    Management of fisheries that exploit mixed-stock populations relies on assumptions made concerning stock structure and mixing in different areas. To address the problems of accounting for uncertainty when formulating scientific advice for the management of highly migratory fish stocks, management decisions need to be based upon assessment models that represent plausible alternative hypotheses for stock structure and migration patterns of the exploited populations. We present a multi-stock, multi-fleet, multi-area, seasonally structured Bayesian state-space model in which different stocks spawn in spatially different areas and the mixing of these stocks is explicitly accounted for in the absence of sufficient tagging data with which to estimate migration rates. The model is applied to the Northeast Atlantic mackerel Scomber scombrus population, accounting for the annual spawning-feeding-overwintering migration patterns of the three spawning components, together with uncertainty in the extent to which the southern component migrates north to feed and overwinter, and consequently the extent to which it mixes with the other components and is subject to exploitation. The model allows the effect of exploitation on the individual components to be assessed, and the results suggest that the fishing mortality of southern spawning adults was insensitive to the extent to which they migrated north.
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    Open Access
    Electricity supply industry modeling for multiple objectives under demand growth uncertainty
    (Elsevier, 2007) Heinrich, G; Howells, M I; Basson, L; Petrie, J G
    Appropriate energy–environment–economic (E3) modelling provides key information for policy makers in the electricity supply industry (ESI) faced with navigating a sustainable development path. Key challenges include engaging with stakeholder values and preferences, and exploring trade-offs between competing objectives in the face of underlying uncertainty. As a case study we represent the South African ESI using a partial equilibrium E3 modelling approach, and extend the approach to include multiple objectives under selected future uncertainties. This extension is achieved by assigning cost penalties to non-cost attributes to force the model's least-cost objective function to better satisfy non-cost criteria. This paper incorporates aspects of flexibility to demand growth uncertainty into each future expansion alternative by introducing stochastic programming with recourse into the model. Technology lead times are taken into account by the inclusion of a decision node along the time horizon where aspects of real options theory are considered within the planning process. Hedging in the recourse programming is automatically translated from being purely financial, to include the other attributes that the cost penalties represent. From a retrospective analysis of the cost penalties, the correct market signals, can be derived to meet policy goal, with due regard to demand uncertainty.
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    Electricity supply industry modeling for multiple objectives under demand growth uncertainty
    (Elsevier, 2007) Heinrich, G; Basson, L; Howells, M; Petrie, J
    Appropriate energy–environment–economic (E3) modelling provides key information for policy makers in the electricity supply industry (ESI) faced with navigating a sustainable development path. Key challenges include engaging with stakeholder values and preferences, and exploring trade-offs between competing objectives in the face of underlying uncertainty. As a case study we represent the South African ESI using a partial equilibrium E3 modelling approach, and extend the approach to include multiple objectives under selected future uncertainties. This extension is achieved by assigning cost penalties to non-cost attributes to force the model's least-cost objective function to better satisfy non-cost criteria. This paper incorporates aspects of flexibility to demand growth uncertainty into each future expansion alternative by introducing stochastic programming with recourse into the model. Technology lead times are taken into account by the inclusion of a decision node along the time horizon where aspects of real options theory are considered within the planning process. Hedging in the recourse programming is automatically translated from being purely financial, to include the other attributes that the cost penalties represent. From a retrospective analysis of the cost penalties, the correct market signals, can be derived to meet policy goal, with due regard to demand uncertainty.
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    Purported flaws in management strategy evaluation:basic problems or misinterpretations?
    (National Inquiry Services Centre (NISC), 2010) Butterworth, Doug S; Bentley, Nokome; De Oliveira, Jose´ A A; Donovan, Gregory P; Kell, Laurence T; Parma, Ana M; Punt, Andre´ E; Sainsbury, Keith J; Smith, Anthony D M; Stokes, Kevin T
    Rochet and Rice, while recognizing management strategy evaluation (MSE) as an important step forward in fisheries management, level a number of criticisms at its implementation. Some of their points are sound, such as the need for care in representing uncertainties and for thorough documentation of the process. However, others evidence important misunderstandings. Although the difficulties in estimating tail probabilities and risks, as discussed by Rochet and Rice, are well known, their arguments that Efron's non-parametric bootstrap re-sampling method underestimates the probabilities of low values are flawed. In any case, though, the focus of MSEs is primarily on comparing performance and robustness across alternative management procedures (MPs), rather than on estimating absolute levels of risk. Qualitative methods can augment MSE, but their limitations also need to be recognized. Intelligence certainly needs to play a role in fisheries management, but not at the level of tinkering in the provision of annual advice, which Rochet and Rice apparently advocate, inter alia because this runs the risk of advice following noise rather than signal. Instead, intelligence should come into play in the exercise of oversight through the process of multiannual reviews of MSE and associated MPs. A number of examples are given of the process of interaction with stakeholders which should characterize MSE.
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    Why a management procedure approach? Some positives and negatives
    (Oxford University Press (OUP), 2007) Butterworth, Doug S
    The origin of the management procedure (MP) approach (sometimes termed management strategy evaluation), with its simulation testing of feedback-control algorithms as a necessary and structured basis for dealing with the inevitable uncertainties associated with fisheries assessments, is briefly reviewed. Also discussed are the advantages that overcome some of the difficulties of the “traditional” approach of coupling an annual “best” assessment to some harvest control rule, such as a failure to consider longer-term trade-offs properly. The MP approach does, however, also have disadvantages, such as the length of time typically required for its development and an argued inflexibility after implementation. Solutions that have been developed to overcome some of these difficulties are discussed.