Feeding Ecology of Thornback Ray, Raja clavata (Linnaeus 1758) in Gökçeada Island, Northern Aegean Sea, Turkey

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

“…The ontogenetic shift of thornback ray was also revealed by previous studies in line with our results of juveniles preferring crustaceans and the contribution of teleost preys increased by growth (Farias et al, 2006(Farias et al, , 2012Saglam & Bascinar, 2008;Daban et al, 2022). This study detected the ontogenetic shift to occur between 40 and 60 cm L T , and specimens between 40 and 50 cm L T had a more balanced diet according to the IRI % and Levin niche width results.…”

“…Nonetheless, its niche breadth was found to be narrower in Sea of Marmara, compared to the eastern Mediterranean (Levin's index: 0.80). The trophic level TLsca was previously reported between 3.20 and 4.14 (Daban et al, 2022;Ebert & Bizzarro, 2008;Ellis et al, 1996;Morato et al, 2003;Yemis ¸ken et al, 2018) which were lower than the results of this study (TLsca = 4.21). Dietary overlap between relatively smaller size groups (size I and size II with 0.91% Pianka index) is related to similar niche breadths, and prey preferences according to similar depth distribution.…”

“…The SCA results of this study showed the ontogenetic shift in prey groups by size; whereas juveniles feed on mainly crustacean prey items, adults prefer mainly teleosts. Previous studies in the Mediterranean and the Black Sea also reported that their main prey items were primarily crustaceans, followed by teleosts (Daban et al, 2022;Eronat & Özaydn, 2015;Saglam & Bascinar, 2008;Šanti c et al, 2012;Yemis ¸ken et al, 2018). In the southern Black Sea, Demirhan et al (2007) reported that its main prey item was European anchovy (Engraulis encrasicolus), especially in the winter period along with the increase in pelagic fish abundance because of southward migration.…”

“…Many benthic fish species have showed changes in species' diets throughout their ontogeny (Munä Oz & Ojeda, 1998). Previous studies revealed that body size is directly affecting R. clavata's feeding strategies (Daban et al, 2022;Demirhan et al, 2007;Yigin & Ismen, 2010) similar to other fish species. Nonetheless, growing body size, mouth dimension and developed swimming capability could increase the ability of prey capture (Karpouzi & Stergiou, 2003).…”

“…Despite its vulnerable status and the most common batoid species, prior research on this species in the Marmara Sea has only covered stock status and its length-weight relationship with the basic meristic features (Demirel et al, 2020;Demirel & Dalkara, 2012;_ Is ¸men et al, 2018). Nevertheless, trophic ecology and feeding behaviour of species are well described in the predominantly west coast (Barría et al, 2015) and east coast (Saglam & Bascinar, 2008;Yemis ¸ken et al, 2018) parts of the Mediterranean (Daban et al, 2022;Demirhan et al, 2007;Eronat & Özaydn, 2015;Kadri et al, 2014;Šanti c et al, 2012).…”