Balancing fishing effort along the tropical tuna abundance-size spectrum Tidd, A. Tolotti, M. T. /Guillotreau, Patrice /Barrier, Nicolas /Dagorn, Laurent Sustainability Balanced harvest Tunas Indian ocean Fishing fleets Fleet-based management The ecosystem approach to fisheries is widely recognised as a key management goal, yet its definition and implementation remain debated. Most fisheries management relies on single-species strategies with technical measures to reduce bycatch. However, selective removals disrupt species composition, affecting ecosystem dynamics and resilience. We present a proof-of-concept model based on balanced harvesting that allocates fishing pressure proportionally across three tuna stocks-yellowfin (Thunnus albacares), skipjack (Katsuwonus pelamis), and bigeye tuna (Thunnus obesus)-in the Indian Ocean according to their size-biomass ratios. The model optimises fishing effort by gear using a predefined objective function based on length-based population dynamics, ensuring a balanced harvest while maintaining each tuna species' biomass within its maximum sustainable yield (BMSY) limit. By assigning fishing mortality (F-multiplier) to each fleet, the model aims to maintain, within the bounds of BMSY for each stock, the ecosystem structure (based on size-abundance relationships) over a 20-year simulation. Results indicate significant reductions in fishing mortality across gears relative to 2020 levels. While some gears, such as purse seine free-school, show increased catches and revenues (146%), others, like purse seine log-school, experience declines (-22%). Overall, fishing at BMSY improves total revenues and catches by 51% and 34%, respectively, compared to 2020. This work demonstrates that it is possible to maintain each tuna stock within BMSY bounds by managing fishing fleets while preserving ecosystem structure, a significant goal of the ecosystem approach to fisheries. 2026 text https://www.documentation.ird.fr/hor/fdi:010096282 fdi:010096282 Tidd A., Tolotti M. T., Guillotreau Patrice, Barrier Nicolas, Dagorn Laurent. Balancing fishing effort along the tropical tuna abundance-size spectrum. 2026, 514, 111495 [10 p.] EN OCEAN INDIEN