Feeding ecology and trophic interactions of the narrow-barred Spanish Mackerel ( <i>Scomberomorus commerson</i> ) 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 (<i>Scomberomorus commerson</i>) 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. <i>Sardinella lemuru</i>, <i>Decapterus</i> spp., and <i>Trichiurus</i> spp. dominated the diet of smaller individuals, while larger fish primarily consumed <i>Decapterus</i> spp. and <i>Mene maculata</i>. <i>Sardinella lemuru</i> and <i>Trichiurus</i> spp. were more abundant in summer and autumn-winter, respectively. In the meanwhile, <i>Decapterus</i> spp. remained important year-round. Isotopic analysis further revealed that <i>Sardinella lemuru</i>, <i>Etrumeus micropus</i>, <i>Decapterus macarellus</i> and Penaeidae (<i>Metapenaeopsis barbata</i>) were dominant prey in smaller size classes, while <i>Encrasicholina punctifer</i>, <i>D. macarellus</i>, <i>Evynnis cardinalis</i>, <i>Trichiurus</i> spp. and <i>Uroteuthis</i> spp. were prevalent in intermediate and larger individuals. The estimated trophic position (3.8-4.3; mean = 4.0) confirms that <i>S. commerson</i> 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.