Feeding habits and trophic levels of elasmobranch species in the Sea of Marmara

Elasmobranch plays an essential role in balancing and sustaining ecosystems through their interactions with various species and with the habitat. In ecosystems that have been subjected to overfishing, it is essential to have information about the trophic ecology of these species. For this reason, in this dissertation, the feeding behavior and trophic levels of Elasmobranchii species obtained on a seasonal basis from the Sea of Marmara between December 2017 and December 2018, was determined using stable carbon and nitrogen isotopes with stomach content analysis. While Crustacea is the main prey item for Mustelus mustelus and Mustelus asterias, Teleostei group was determined as the main prey item for S. acanthias, S. canicula, D. pastinaca, T. marmorata, and R. clavata. M. aquila which mainly feeds on Mollusca has the lowest Levins niche breadth and is determined as a specialist predator species. According to results of stable isotope analysis and stomach content analysis, S. acanthias is a generalist predator species, and feeds on Teleostei among the short and long timescale. The Pianka index was showed that, the high niche overlap between M. mustelus to M. asterias. Also, according to the results of the isotopic niche overlap; the hight niche overlap was found between Scyliorhinus canicula and juvenile Raja clavata and Squalus acanthias species. With the exception of Myliobatis aquila and Mustelus asterias, the Levins niche breadth of the other species were found to be quite similar. Apart from these two species, other species have been determined as generalist predator species. According to the stomach content analysis results, the highest trophic level was S. acanthias, while the lowest one was M. asterias. However, the species with the highest trophic level was determined as Oxynotus centrina by stable isotope analysis.