Some Observations on the Role of Trophodynamic Models for Ecosystem Approaches to Fisheries

Useful trophodynamic models within an ecosystem approach to fisheries need to be simple enough that we can actually learn from them, but complex enough that we can believe that their results are reliable. Reliability is commonly assessed by comparing model outputs with data, but many food web models grow in complexity very quickly while the sources of information to parameterize and evaluate them do not grow as fast. Within the diversity of modeling frameworks currently available, their adequacy for addressing management issues largely depends on the scope and specific goals of the modeling exercise (e.g., exploration of competing hypotheses, strategic advice, tactical advice). Nonetheless, any management-oriented implementation needs to attain a balance between uncertainty and realism, and optimal model performance is expected to be achieved at some intermediate level of complexity. Furthermore, trophodynamic models can capture key aspects of ecosystem dynamics, but implementing ecosystem approaches to fisheries will also require integrating this dynamics and its uncertainty with all other aspects of the management process. One natural way of doing this is by considering trophody-namic models as operating models within a management strategy evaluation framework. Highly complex ecosystem models can be used to fulfill this role, but simpler models (e.g., “minimum realistic models [MRM]”) are likely to be a better starting point. Recent advances in food web theory can provide useful building blocks and guidance for developing these “minimum realistic models.” Although these models can be good candidates for capturing the joint dynamics of core components of the system, we can never be that we are not missing something important. Due to this fundamental uncertainty, embedding these simple trophodynamic models into management strategy evaluation frameworks and pursuing multiple modeling approaches can provide a sensible venue for assessing the robustness of management strategies to our alternative ways of representing trophodynamic effects. Also, because “minimum realistic models” are focused on a relatively small number of ecosystem components, they are well suited for matching their data requirements with operationally feasible monitoring programs. Despite the specific modeling approaches we choose, developing these operating models in conjunction with field programs that can provide the appropriate data to parameterize them and to assess their performance is fundamental to achieve reliable trophodynamic models for ecosystem approaches to fisheries.