Influence of environmental parameters on the abundance, biodiversity and distribution of demersal elasmobranchs in the eastern Sea of Marmara, with a focus on deoxygenation

This study investigates the influence of environmental parameters on the abundance, biomass, and spatial distribution of demersal elasmobranchs in the eastern Sea of Marmara over a ten-year period (2014–2024). Catch per unit effort (CPUE) data from bottom trawl surveys were combined with in situ measurements of dissolved oxygen, temperature, salinity and depth. Multivariate analyses indicate that dissolved oxygen and temperature are key factors associated with spatial variability of demersal elasmobranchs in the investigated area. Temporal patterns show an increase in their abundance until the late 2010s, followed by a marked decline, which may reflect increasing environmental stress as a cause of the decline. These findings suggest that ongoing deoxygenation, together with other environmental parameters, may play an important role in structuring demersal elasmobranch assemblages in the region.