Based on the trophic field overlap of species in the food webs, we propose using the weighted trophic field overlap (WTO) to determine the uniqueness of species in a topological network by considering the food web structure and the proportions of prey in the diets of predators. This proposed method measures uniqueness structurally and mathematically and considers cannibalism and mutual predation between species to overcome the deficiencies of the traditional method (the sum of trophic field overlap, STO), which only relies on the topological structure of the food web. Species with the lowest WTO values have high interaction strengths with other species in the food web weighted by the proportion of prey and play important roles as prey in the initial ecosystem, which are not recognized by the traditional method. The proposed index is sensitive to changes in the diets of predators since slight fluctuations may cause the index to vary considerably. The proposed methodology could be extended to other marine ecosystems to identify unique species from a practical and dynamic perspective and will contribute to the protection of unique species that maintain the trophic diversity of food webs and ecosystem robustness. •A WTO index was proposed for identifying unique species in food webs.•This index considers both the topological network structure and proportion of prey.•Cannibalism and mutual predation between species are also accounted for.