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With the development of fisheries research, there has been a gradual shift from a single species management model to an ecosystem based fisheries management model (EBFM). The concept of EBFM is increasingly accepted by researchers and regional fisheries management organizations, but there is little relevant research and application in Indian Ocean tuna fisheries. In this study, a multi species ecological model (LeMaRns) based on body length structure was constructed based on publicly available data and studies from the Indian Ocean Tuna Commission (IOTC) to analyse the effects of different fishing fleets on stock status and ecosystem structure under different fishing effort. The results of the study showed that an increase in fishing effort resulted in a decrease in population biomass and that predatory and competitive relationships between species also influenced changes in population biomass. Two ecosystem indicators, Large Fish Index (LFI) and Mean Maximum Length (MML), may be more sensitive to the longline (LL) fleet, and both LFI and MML showed a decreasing trend with increasing fishing effort, suggesting that the proportion of small and medium sized individuals in the community is increasing, which can have important implications for the stability of ecosystem structure. As fishing effort continued to increase, the number of stocks at risk of collapse began to gradually increase, and the number of stocks at risk of collapse may be more sensitive to the longline (LL) fleet. Therefore, inter species relationships and the impacts of different fishing fleets on stock dynamics and marine ecosystems need to be fully considered in future fisheries management.
