AbstractGascuel, D., Guénette, S., and Pauly, D. 2011. The trophic-level-based ecosystem modelling approach: theoretical overview and practical uses. – ICES Journal of Marine Science, 68: 1403–1416. A trophic-level (TL)-based ecosystem modelling approach is presented, where ecosystem functioning is modelled as a flow of biomass up the foodweb through predation and ontogenetic processes. The approach, based on simple equations derived from fluid dynamics, provides insights into ecosystem functioning and the impact of fishing. A virtual ecosystem is simulated and the model shown to be capable of mimicking the effects of various exploitation patterns on ecosystem biomass expected from the theory. It provides the theoretical basis to explain complex patterns, such as cascading effects, maximum sustainable ecosystem yield, and fishing down the foodweb. The utility of the TL-based approach as a practical tool for determining fishing impacts in specific ecosystems is illustrated using the Guinean ecosystem as a case study, showing how current fishing effort levels led to full exploitation of higher TLs, confirming and generalizing previous single-species assessment results. Finally, catch trophic spectrum analysis is presented to show that it provides reliable biomass estimates when catches per TL and primary production are known.