Ontogenetic shift in diet and trophic role of Raja clavata inferred by stable isotopes and stomach content analysis in the Sea of Marmara

Abstract

Trophic ecology studies on predator-prey interactions reveal insights into ecological communities and help understand a species' role in the food web by contributing to improved fisheries management and conservation capabilities. Understanding the ecological role of overexploited and endangered predators is essential to deciphering how their feeding behavior influences food web dynamics. Here, we investigated the feeding behavior of the common and IUCN-listed Near Threatened (NT) thornback ray Raja clavata, using carbon and nitrogen stable isotope and stomach content analysis. It has recently suffered an 87 % decline in reported catches from the Sea of Marmara within the last decade. These results show that thornback ray mainly feeds on teleost species, except in summer, with both methods showing this species changes its diet ontogenetically by stomach content analysis. This ontogenetic diet shift was at lengths 40-50 cm by changing group preferences from Crustacea to Teleostei. MixSIAR results showed that both adult and juvenile individuals of R. clavata feed mainly on the crustaceans, but the contribution of teleosts represented by Trachurus sp. was very low (<15%). The trophic position increased total length and was higher than other batoid species in the Sea of Marmara.