Marine ecosystem models, particularly Ecopath with Ecosim (EwE), are pivotal in simulating complex policy scenarios involving diverse species, environmental pressures, and ecosystem services. These models are increasingly indispensable for the practical implementation of ecosystem-based management strategies in natural resource conservation. They provide a framework for conveying evidence and advice, focusing on trade-offs, risks, and uncertainties inherent in ecosystem-based management.
The growing emphasis on ecosystem approaches in decision-making processes, especially in the context of cumulative pressure assessment in rapidly changing marine environments, has led to a heightened reliance on EwE and similar models. These tools are becoming integral for advisors and decision-makers, including organizations like ICES, in shaping management and policy decisions.
The integration of ecosystem approaches into policy and management frameworks is expected to have extensive socio-economic implications for a wide range of stakeholders. Consequently, it is critical to ensure that EwE models adhere to best practices and undergo thorough review processes. Addressing challenges such as data limitations, imprecision in observations, and uncertainties in input parameters is essential. A key aspect that requires careful attention is the process of model calibration. The influence of different calibration strategies on parameter estimation within EwE models is a subject that demands further exploration and understanding, particularly regarding the sensitivity of model outputs to various calibration methods.
In this Editor's Choice article, the authors investigate the principles of parameter estimation in EwE models and the diverse calibration approaches employed over the years. The focus is on the estimation of "vulnerability multipliers", which are critical in determining the consumption rate limits of predators within these models.
The article presents two case studies to illustrate the implications of EwE model calibration. The first employs a conceptual model and simulations to examine the emergence of vulnerability multipliers and their dependence on data quality and calibration strategies. The second case study assesses how alternate calibration approaches affect the ecosystem information derived from two operationally used EwE models, including estimates of Fishing Mortality at Maximum Sustainable Yield (FMSY) and ecosystem indicators.
Throughout the article and within the case study results, the authors demonstrate how judgemental evaluation, ecological reasoning, and hypothesis testing should support the calibration procedure. As EwE approaches its 40-year milestone, this study contributes significantly to the body of knowledge on EwE best practices. It provides valuable recommendations for evaluating the appropriateness of vulnerability multipliers and their impact on the uncertainty of model outputs.
Read the full paper, Calibrating ecosystem models to support ecosystem-based management of marine systems, in ICES Journal of Marine Science.
Components of ecosystem model calibration and recommendations for assessment. Click to enlarge.
Calibrating ecosystem models to support ecosystem-based management of marine systems
Jacob W. Bentley, David Chagaris, Marta Coll, Johanna J. Heymans, Natalia Serpetti, Carl J. Walters, Villy Christensen