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

Abstract

The dietary composition and nutritional alteration resulting from time and size of thornback ray, Raja clavata, were investigated in the present research. For this purpose, the individuals were obtained from the commercial bottom trawl vessels operated around Gökçeada Island, North Aegean Sea, Turkey between February 2019 and February 2020. The female:male ratio was found to be 1:0.79. The vacuity index was calculated for males, females and both individuals to be 5.8%, 4.7%, and 5.3%, respectively. The major food item groups were determined to be decapod crustaceans, teleost fish, and cepholopoda with IRI% (Index of Relative Importance) values of 77.72, 7.05, and 0.25, respectively. The best-represented food item was found to be Goneplax rhomboides. The prey types, abundance, and biodiversity were observed to change with the increasing lengths of R. clavata. The trophic level (TLw) of R. clavata was calculated to be 3.27, and it was observed that the TLw values were increased with the increasing individual length. The diet overlap was found to range from 40 to 49 cm and 50 to 59 cm TL in autumn and winter. The highest prey biodiversity was found in the length group of 70–85 cm TL and during spring. This study presents detailed findings on the feeding behaviour of R. clavata. In the future, food competition between the species should be monitored to develop a better understanding of the diet overlap. Thus, more comparisons should be conducted between the studies performed in varied geographical areas.