Model uncertainty in the ecosystem approach to fisheries

Abstract

Fisheries scientists habitually consider uncertainty in parameter values, but often neglect uncertainty about model structure. The importance of this latter source of uncertainty is likely to increase with the greater emphasis on ecosystem models in the move to an ecosystem approach to fisheries (EAF). It is therefore necessary to increase awareness about pragmatic approaches with which fisheries modellers and managers can account for model uncertainty and so we review current ways of dealing with model uncertainty in fisheries and other disciplines. These all involve considering a set of alternative models representing different structural assumptions, but differ in how those models are used. The models can be used to identify bounds on possible outcomes, find management actions that will perform adequately irrespective of the true model, find management actions that best achieve one or more objectives given weights assigned to each model, or formalise hypotheses for evaluation through experimentation. Data availability is likely to limit the use of approaches that involve weighting alternative models in an ecosystem setting, and the cost of experimentation is likely to limit its use. Practical implementation of the EAF should therefore be based on management approaches that acknowledge the uncertainty inherent in model predictions and are robust to it. Model results must be presented in a way that represents the risks and trade-offs associated with alternative actions and the degree of uncertainty in predictions. This presentation should not disguise the fact that, in many cases, estimates of model uncertainty may be based on subjective criteria. The problem of model uncertainty is far from unique to fisheries, 3 and coordination among fisheries modellers and modellers from other communities will therefore be useful.Keywords Bayesian methods, Ecosystem Approach to Fisheries, ecosystem models, fisheries management, model uncertainty, operational management procedures. Abstract

From strategic ambiguity to technical reference points in the Antarctic krill fishery: the worst journey in the world?

“…Evaluation approaches often use models to simulate the effect of management measures on the future state of the ecosystem (Rademeyer et al 2007). Such simulations are inevitably uncertain, and the models should therefore provide probabilistic estimates of future state (Hill et al 2007a). Soft reference points specify both a desirable state and a probability of the ecosystem being in that state.…”

“…It is appropriate to present unaggregated results for the most important components (deYoung et al 2004;Hill et al 2006). Nonetheless, Hill et al (2007a) advise using no more than seven separate pieces of information in decision making. Aggregation might therefore be essential, as might weighting components by importance to ensure that they appropriately influence the average.…”

Up the ante on bioeconomic submodels of marine food webs: A data assimilation-based approach

“…We also think data assimilation methods like the ensemble Kalman lter points to better models that serve towards economic decision analysis. Ultimately and in the broader scope of things, we need to develop methods and frameworks that are appropriate for the dimensionality, nonlinearity and stochasticity inherent in ecosystem-based sheries managemet, all in a holistic view (Hill et al, 2007;Link, 2010;Fulton et al, 2011). In this perspective, our work may be a small step, but nevertheless a step in the right direction.…”

From Ice to Penguins: The Role of Mathematics in Antarctic Research

“…interactions was to use multiple plausible "scenarios" or plausible representations of 27! the system (Hill et al 2007b). The word "scenario" here means a model and its data 28!…”

“…control and characterize the uncertainty that often multiplies as models integrate more 27! processes (Hill et al 2007b Figure 2. The Antarctic continent and the Southern Ocean which surrounds it.…”