Using a visual deterrent to reduce seabird interactions with gillnets

Bycatch is one of the main threats to seabird conservation. In Portugal, there are alarming estimates of seabirds bycaught per year in bottom gillnet fisheries, which get entangled during fishing operations, when the gear is close to the surface. In this study, a visual deterrent (scarybird) was tested in a fishing vessel operating bottom gillnets near and within Berlengas Islands SPA (Special Protection Area). Trials were conducted between 2019 and 2020, with 18 control and experimental fishing trips monitored by a trained observer. The scarybird proved to be an effective bird deterrent measure, affecting both the numbers and distribution of seabirds and keeping a large portion of birds away from the vessel during fishing operations, making them potentially less vulnerable to bycatch. The deterrent device was more effective in the closest area to the vessel (0–20 m) where there was a significant reduction in the number of gulls (Larus michahellis/fuscus, −56 %) and northern gannets (Morus bassanus, −72 %) close to the vessel, by comparison to control fishing trips. The use of this aerial deterrent device had no impact on the fishery's target catches and revenue, which contributed to a good acceptance by fishermen. This simple and “easy to implement” deterrent device has potential to be further tested as a bycatch mitigation measure in bottom gillnets but also in other gears, whenever interactions with birds occur mainly close to the surface.