Feeding ecology and trophic interactions of the narrow-barred Spanish Mackerel (Scomberomorus commerson) in the Central Taiwan Strait.

Understanding the foraging ecology of marine predators is essential for ecosystem-based fisheries management. This study examined the diet of the narrow-barred Spanish mackerel (Scomberomorus commerson) in the Central Taiwan Strait using stomach content and stable isotope analyses integrated with an isotopic mixing model. A total of 1,733 specimens were collected between January 2017 and March 2022. Stomach content analysis revealed that 79.8% had empty stomachs, while the remainder mainly contained semi-digested fish remains. Among identifiable prey, composition varied by size and season. Sardinella lemuru, Decapterus spp., and Trichiurus spp. dominated the diet of smaller individuals, while larger fish primarily consumed Decapterus spp. and Mene maculata. Sardinella lemuru and Trichiurus spp. were more abundant in summer and autumn-winter, respectively. In the meanwhile, Decapterus spp. remained important year-round. Isotopic analysis further revealed that Sardinella lemuru, Etrumeus micropus, Decapterus macarellus and Penaeidae (Metapenaeopsis barbata) were dominant prey in smaller size classes, while Encrasicholina punctifer, D. macarellus, Evynnis cardinalis, Trichiurus spp. and Uroteuthis spp. were prevalent in intermediate and larger individuals. The estimated trophic position (3.8-4.3; mean = 4.0) confirms that S. commerson functions as a top predator with opportunistic feeding behavior. These findings improve understanding of regional trophic dynamics and support sustainable fisheries management in the Central Taiwan Strait.