Conservation actions to reduce Tursiops truncatus depredation on static net small-scale fisheries in the Mediterranean Sea

Depredation by bottlenose dolphins (Tursiops truncatus) on static-net small-scale fisheries poses significant challenges for both marine conservation and the fishing community in the Mediterranean Sea. This study explores two mitigation actions aimed at reducing depredation and to promote sustainable fisheries and dolphin population conservation. Acoustic and catch data were collected across two Sardinian sites to assess practical implementation and fishermen's acceptance of these measures. Thus the aim of this study was to determine the effectiveness of an acoustic deterrent device (pinger) to reduce depredation on trammel and gill nets and of using a small trap in place of traditional trammel nets as a mitigation tool. For each fishing operation (net with pinger vs. control net; traps vs. trammel net), catch data were collected and the catch per unit effort (CPUE) and species’ richness were obtained and analyzed using Generalized Linear Models. The presence of bottlenose dolphins decreased the CPUE on nets by 50 to 70 kilograms. The CPUE was higher for gillnets in comparison to trammel nets and on nets with pingers in comparison to nets without. The presence of the pinger and the type of net used did not influence species richness; the latter was only influenced by the presence of bottlenose dolphins. Regarding traps versus trammel nets, the average species richness was significantly higher in trammel nets but average CPUE was significantly higher in traps. While no single solution was proven to be universally effective, a combination of tailored approaches can potentially reduce depredation incidents. Our results underscore the need for an adaptive management framework that integrates scientific research, technological innovations, and socio-economic considerations to achieve long-term sustainability for both marine biodiversity and small-scale fisheries in the Mediterranean Sea. This study also highlights the importance of continuing to involve local fishing communities in the design and implementation of conservation strategies to enhance compliance and efficacy.