Chondrichthyes in the north-western Ionian Sea (central Mediterranean): Species diversity, abundance and spatio-temporal changes

This study provides an updated list of fish in the Class Chondrichthyes sampled during all research projects conducted in the north-western Ionian Sea from 1985 to 2020. A total of 36 Chondrichthyes species belonging to 8 orders and 19 families were detected, most of them distributed over a wide depth range, between shelf and slope. For species assessed by the International Union for Conservation of Nature (IUCN), 8 species are listed as Critically Endangered, 3 as Endangered, 6 Vulnerable and 5 as Near Threatened species. The distribution of cartilaginous fish was examined exploring the historical series of MEDITS data (1995–2020. Changes in the species diversity and in their abundance with time and space were detected and some environmental and anthropogenic drivers that could have caused these changes were analysed. An increase in the presence, number of species and biomass of Chondrichthyes was detected from 1995 to 2020. The GAM analyses seem to indicate that the observed increase in species number and biomass is due to the decrease in fishing capacity and increase in salinity and temperature on the bottom. Furthermore, for the most abundant species, Galeus melastomus, an increase of biomass, size and a deeper distribution over the last 26 years were detected. Significant changes in biomass were also observed for other abundant species in the study area (Scyliorhinus canicula and Raja miraletus). The increase in biomass over time, different from several Mediterranean observations, is discussed in relation to the presence of refuge areas in the north-western Ionian Sea.