Spatio-temporal density of the demersal Chondrichthyes assemblage in an upper bathyal of the eastern Mediterranean Sea

Abstract

Chondrichthyans are a very important taxon that plays a top predator role in the trophic level of the food web, and species are particularly vulnerable to exploitation in the marine ecosystem. The deep waters of the eastern Mediterranean Sea have been less studied than the continental shelf, especially for the chondrichthyans. Therefore, the present study was conducted to investigate the spatio-temporal distribution of chondrichthyans collected monthly in eight different (200–900 m) depth strata during different periods (2010–2011 and 2019–2021) using an otter bottom trawl. A total of 17 species were identified in upper bathyal, composed of 6 batoids, 10 sharks, and one chimaera. The constant species (dominance: DO% > 50) in the study area were Galeus melastomus, Scyliorhinus canicula, Etmopterus spinax, and Raja clavata. The most abundant species was E. spinax, followed by G. melastomus. Fourteen and 15 species were caught during the first and the second survey, respectively. Biodiversity characteristics (number of species, abundance, and diversity indices) varied only with bottom depth. Two different depthwise assemblages were estimated along the bottom depth gradient; ≤ 500 m and > 500 m. The discriminator species were R. clavata, S. canicula, G. melastomus, Dipturus oxyrinchus, and Squalus blainville found on the upper slope and E. spinax, G. melastomus, and Centrophorus cf. uyato found on the lower slope. With our results, total number of demersal chondrichthyan species found in the bottom (bathyal and continental shelf) of Antalya Bay was reached to 26 species.