Trophic ecology of the deep-sea skate Dipturus oxyrinchus (Linnaeus, 1758) in the bathyal food web of the central Mediterranean Sea

Abstract

The Mediterranean Sea is a biodiversity hotspot where most elasmobranchs are severely threatened, and there is limited knowledge regarding life history traits and trophic ecology. In this context, our study focuses on the trophic ecology of the longnose skate (Dipturus oxyrinchus) in the Strait of Sicily (central Mediterranean), which is designated as an Important Shark and Ray Area. The objectives of the present study were to investigate the main changes in the feeding habits of the species according to ontogeny and bathymetric distribution. We collected 152 specimens at depths between 200 and 700 m from 2016 to 2019. The combination of stomach content and stable isotope analyses allowed to classify the longnose skate as a generalist feeder, with a diet dominated by crustaceans, and smaller contributions of bony fish and cephalopods. The most consumed crustaceans were decapods (including Parapenaeus longirostris, Iridonida speciosa, Chlorotocus crassicornis) and mysids (Lophogaster typicus). Multivariate analyses indicated that predator total length and collection depth had a significant effect on the prey consumption patterns, which was corroborated by General Additive Models (GAM), allowing determination of the most commonly consumed prey. Significant ontogenetic changes were observed, with smaller individuals primarily preying upon benthic organisms and larger individuals adopting a more benthopelagic diet, reflected by a slight increase in trophic position. This study highlights the role of the longnose skate within the bathyal food web of the Strait of Sicily, providing useful information for ecosystem modelling, which will support effective conservation strategies.