The use of conceptual models to structure stock assessments: A tool for collaboration and for “modelling what to model”

Conceptual models are simplified representations of the main components and processes of a dynamic system, the mechanisms by which they are related, and the ways they are observed (i.e., the data generating processes). Constructing a conceptual model (CM) should be the first step when planning a new stock assessment or updating previous assessments, because it can improve the modelling process by guiding the workflow and “modelling what to model”. CMs should be built by summarizing information about a system while also proposing hypotheses or assumptions about the uncertainties and unknown aspects. Several steps are necessary to build a CM: 1) gather known information about the species and the fisheries that interact with it, 2) state the objectives of the stock assessment, 3) define the spatial scale, 4) define the temporal scale, and 5) outline components and processes of the system (biological, fisheries and observation processes) and what drives them. Initial draft CMs should be based on the best available science and constructed using the fundamental principles of ecology, socioecology, fisheries and other relevant sciences. CMs offer a framework for integrating knowledge across domains, and benefit from an elicitation process. The elicitation process is a set of deliberate activities (e.g., workshops) that allow other experts and relevant parties to contribute with their knowledge to enrich draft CMs. CMs are not static entities but rather dynamic constructs that can identify future research directions and evolve to incorporate new insights and knowledge. Fisheries systems for highly migratory pelagic species in the Pacific Ocean (north Pacific Albacore tuna, eastern Pacific Dorado, and south Pacific Swordfish) are used as examples to illustrate how to develop CMs, and demonstrate improvements to the subsequent assessment models following development of the CMs.