The present study presents an electronic decision-support tool that uses a fuzzy-logic model of expert knowledge to assist in multi-criteria decision-making in the context of an Ecosystem Approach to Fisheries (EAF). The prototype model integrates the multiple goals and objectives related to the evaluation of the ecosystem performance of the South African sardine Sardinops sagax fishery into a NetWeaver knowledge base and provides intuitive visual outputs to communicate results to managers and stakeholders. The software tool was developed in a consultative process with key experts and follows the hierarchical tree approach recommended in the FAO guidelines for responsible fisheries. Input variables are based both on quantitative data and expert opinion. We evaluated the model in terms of robustness to input changes, influence of system structure, and appropriateness of input scales for parameters based on expert opinion. Results show that the model is robust and conservative. The strength of the approach lies in the ability to include variables that are difficult to measure. It provides a means of rendering value judgements explicit and transparent. The tool synthesises a large amount of information and aims at improving understanding rather than achieving precision. The system has the potential to have wide application in the context of EAF.