Trophic niche partitioning during ontogeny in three skate species, Raja brachyura, Raja clavata, and Raja montagui, in the Northeast Atlantic

Niche partitioning enables ecologically similar species with overlapping resource requirements to coexist. This study examines dietary niche partitioning in three sympatric skate species Raja brachyura , R. clavata and R. montagui in the North Sea and English Channel. Stomach content analysis (SCA) and stable isotope analysis (SIA) were used to compare diets between species, sex, and length class. Stomachs from 111 R. brachyura , 234 R. clavata , and 99 R. montagui were analysed using the prey-specific index of relative importance ( %PSIRI ). SCA showed small individuals (< 35cm L T ) of all species consumed diets dominated by Caridea species (> 63.9 %PSIRI ). As size increased, an ontogenetic diet shift was observed until 55 cm L T for all species, regardless of maturity stage or maximum attainable length. Larger individuals above 55 L T showed significant differences in diet among species. R. brachyura , consumed large amounts of teleost species (> 70.6 %PSIRI ), R. clavata predominantly consumed brachyuran crabs (> 57.2 %PSIRI ), and R. montagui consumed a mix of brachyuran crabs (33.0 %PSIRI ) and teleost species (43.2 %PSIRI ). SIA showed interspecific differences in the isotopic niche space between the three skate species, but no intraspecific differences across length classes. The results from this study are similar to patterns found in diet studies of other sympatric skate species where small individuals primarily consume Caridea species, and niche partitioning is observed for larger individuals. This knowledge is essential for ecosystem-based management approaches, especially in areas such as the North Sea, where these species share habitat areas with fishing operations. • Small individuals (< 55 cm L T ) showed similar diets among the three skate species • Ontogenetic diet shifts occur irrespective of maturity stage or maximum length • Diets of large individuals (≥ 55 cm L T ) differed significantly between all species