Prey selection patterns of bottlenose dolphins depredating bottom-set gillnets in the northern Aegean Sea

Abstract

Understanding the foraging strategies of marine megafauna that interact with fisheries is key to conflict mitigation. Bottlenose dolphins Tursiops truncatus in the northern Aegean Sea frequently depredate bottom-set nets, but whether they exhibit prey selection within depredation events remains unknown. We conducted 80 fishing trials over 2 seasons (2020 and 2021) using gillnets in the Thermaikos Gulf, and investigated patterns in the catch and gear damage to determine whether bottlenose dolphins target certain genera over others. A high preference index was calculated for demersal fish like Mullus and Trachurus, as well as less frequently occurring pelagic fishes like Sphyraena. We also found a strong indication that dolphins target certain sizes of fish in certain genera, namely the shorter specimens of larger fishes and the larger specimens of shorter fishes. In conjunction with the patterns in the vertical position of holes torn in the nets, our findings suggest that bottlenose dolphins take advantage of whichever fish are seasonally prevalent.