Abstract:
The overlap of cetacean habitats and fishing grounds leads to inevitable interactions, potentially impacting dolphin populations. Delphinus delphis, classified as “endangered” in the Mediterranean, is among the species affected. This study investigates the resource overlap between various fisheries (trawlers, purse seiners and others) and the D. delphis population in the central Aegean Sea, Greece. It aims to evaluate
coexistence and assess policy effectiveness. Dolphin abundance was estimated from sightings recorded between 2015 and 2023 in the central Aegean Sea, and their diet preferences were established through a systematic review. Data on annual fishery landings was sourced from the Hellenic Statistical Authority. The Pianka Index was used to measure the overlap between the species caught with various fishing gear types
and those preyed upon by D. delphis. The values ranged from 0 (no overlap) to 1 (complete overlap). The encounter rate was 1.158 D. delphis /100km, with each dolphin predicted to consume 1.78 tons of fish annually. Considering the estimated population size, 404.11 tons of targeted species are preyed upon annually by the D. delphis population in the central Aegean Sea. With data from all fisheries, it was estimated that a total of 4,840.17 tons of prey species for D. delphis was landed annually. The Pianka Index revealed an overlap of 0.389 with trawlers, 0.132 with purse seines, and 0.171 with other gear types. This highlights the vulnerability of specific landing groups and the robust overlap between fisheries and dolphins targeting the same species. Moreover, despite Greece’s membership in the General Fisheries Commission for the Mediterranean, the Aegean Sea ranks second in Illegal, Unreported and Unregulated (IUU) fishing due to trawling violations. This signifies the need for policy reinforcement and sustainable solutions, involving fishers and policymakers to integrate an efficient, ecosystem-based management approach.
coexistence and assess policy effectiveness. Dolphin abundance was estimated from sightings recorded between 2015 and 2023 in the central Aegean Sea, and their diet preferences were established through a systematic review. Data on annual fishery landings was sourced from the Hellenic Statistical Authority. The Pianka Index was used to measure the overlap between the species caught with various fishing gear types
and those preyed upon by D. delphis. The values ranged from 0 (no overlap) to 1 (complete overlap). The encounter rate was 1.158 D. delphis /100km, with each dolphin predicted to consume 1.78 tons of fish annually. Considering the estimated population size, 404.11 tons of targeted species are preyed upon annually by the D. delphis population in the central Aegean Sea. With data from all fisheries, it was estimated that a total of 4,840.17 tons of prey species for D. delphis was landed annually. The Pianka Index revealed an overlap of 0.389 with trawlers, 0.132 with purse seines, and 0.171 with other gear types. This highlights the vulnerability of specific landing groups and the robust overlap between fisheries and dolphins targeting the same species. Moreover, despite Greece’s membership in the General Fisheries Commission for the Mediterranean, the Aegean Sea ranks second in Illegal, Unreported and Unregulated (IUU) fishing due to trawling violations. This signifies the need for policy reinforcement and sustainable solutions, involving fishers and policymakers to integrate an efficient, ecosystem-based management approach.
