Dolphin depredation and damage accumulation on different set nets in the northeastern Mediterranean Sea

Abstract

Small-scale fisheries represent an economically marginalized sector, that struggles to balance operational costs and profit from catches. Economic revenues from catches have declined due to overfishing, and additional costs may jeopardise the sustainability of the sector. In Greece, reported net damage from interaction with marine megafauna, especially the bottlenose dolphin (Tursiops truncatus) is a common occurrence for many coastal areas, where small-scale fisheries operate. A seasonal experimental trial took place during 2016–2017 in the northern Aegean Sea, in an area where large actively swimming marine organisms other than dolphins were lacking. Three gangs of different panels of net (mixed gill nets and trammel nets) were deployed in three different depth zones. For each gang, we recorded the number, size, and position of holes on each net, and assessed overall damage. Multifactor analysis was used to identify possible links between fishing practices and damage intensity. Results showed a correlation between reduced net damage by dolphins with larger mesh sizes and increasing depth. In the case of small mesh sizes, one should seek a combination of solutions, as changes in deployment depths alone, do not seem to be adequate for the depth ranges studied. The adoption of larger than 22 mm mesh size is proposed for all set nets, to increase net selectivity and decrease accumulated damage. Fishers should focus on adjusting, substituting or even ceasing specific fishing tactics to have the lowest possible economic loss, whereas fisheries scientists, managers and policy makers must monitor and offer guidance for this transition.