Are multispecies models an improvement on single-species models for measuring fishing impacts on marine ecosystems?

We review the application of multispecies models as tools for evaluating impacts of fishing on marine communities. Four types of model are identified: descriptive multispecies, dynamic multispecies, aggregate system, and dynamic system models. The strengths and weaknesses of multispecies models and their ability to evaluate the causal mechanisms underlying shifts in production are examined. This comparison provides a basis for assessing the benefits of each modelling approach as a tool for evaluating impacts of fishing in marine ecosystems. Benefits of multispecies models include: improved estimates of natural mortality and recruitment; better understanding of spawner-recruit relationships and of variability in growth rates; alternative views on biological reference points; and a framework for evaluating ecosystem properties. Populations are regulated by competition (food limitation), predation, and environmental variability. Each factor may influence different life-history stages, locally or regionally. However, most multispecies models address only a subset of these factors. often aggregated over functionally different species or age groups. Models that incorporate the important interactions at specific stages and scales will be necessary if they are to continue to supplement the information provided by single-species models. (C) 2000 International Council for the Exploration of the Sea.