Monitoring of Elasmobranchs in the Amvrakikos Gulf, Greece: A comparative analysis of Fishery-Dependent and Independent data

Amvrakikos Gulf, an enclosed gulf in western Greece, was delinetaed as an Important Shark and Ray Area (ISRA) in 2023 under the criteria of vulnerability and reproduction for three threatened species: Aetomylaeus bovinus, Gymnura altavela and Mustelus mustelus. The Gulf, a national park and the most extended wetland in Greece, hosts a remarkable diversity of 11 elasmobranch species, of which five are listed as Endangered (EN) and Critically Endangered (CR) by the IUCN Red List of Threatened Species at global level. Considered the importance of data on abundances for conservation purposes, an implementation of an ongoing fishing monitoring activity with fishery-independent data collection was carried out. Surveys took place in summer 2024 and 2025 and consisted in onboard and port surveys for fishery-dependent data collection and the deployment of Baited Remoted Underwater Videos Stations (BRUVS) for fishery-independent data collection. 87 BRUVS deployments, resulting in >94 h of videos, have been carried out, while 158 fishing trips have been surveyed. 67.7%. of the BRUVS deployments were positive for elasmobranchs and the average standardized MaxIND (maximum number of distinct different individuals sighted per deployment) observed was of 1.26 elasmobranchs individuals sighted per hour of deployment. 70.9% of the fishing trips were positive for elasmobranchs and the average standardized CPUE (nr of individuals*1000m-1) was of 2.61 elasmobranchs each 1000 meters of net. The combination of the two methodologies confirmed the presence in the Gulf of 10 species of elasmobranchs, while the previously reported presence of the sandbar shark, Carcharhinus plumbeus, was not confirmed. The analysis carried out for the comparison of the two methodologies showed differences in the composition of the assemblages sampled with BRUVS and with fishing surveys. Dasyatis spp. was the most abundant group in both methodologies, while T. torpedo and T. marmorata have been observed only with fishing surveys and not with BRUVS. 1 For what concerns BRUVS, the study allowed to obtain insights also on the different moments of the day in which the deployments were carried out, the depth, as well as on the different baits used. Results suggest that BRUVS are a successful non-extractive tool to use in Amvrakikos Gulf, particularly when combined with systematic fishery-dependent monitoring, and allowed to obtain insights in abundance and distribution of elasmobranchs inhabiting the gulf.