CCAMLR requires an assessment method for recommending a subdivision of the krill catch limit in Area 48 that will be highly likely to achieve the objectives of the convention despite the uncertainties in knowledge. This will be part of the management procedure governing the krill fishery. The agreed workplan for developing a management procedure includes the evaluation of candidate management procedures in a simulation framework, using plausible models of the Antarctic marine ecosystem. This paper develops a framework for erecting such models. It is divided into three main parts, addressing different aspects of model development. Part 1 outlines the issues to consider in assessing the requirements of plausible models. Part 2 discusses the general model requirements while Part 3 presents a possible framework for developing ecosystem models to evaluate krill management procedures. The first section of this part outlines a conceptual approach to the taxonomic/biological elements of a model and the manner in which linkages between those elements might be considered. The second section details a model framework for characterising (i) the different taxa depending on the status of knowledge and their importance for understanding the ecosystem effects of fishing, (ii) important physical processes that will influence the system and (iii) the fisheries. In developing these parts, the paper highlights areas that may be necessary to be considered by WG-EMM in the development of plausible models.