Unravelling seabird-fishery dynamics through bird-borne technologies

Abstract

[eng] Seabirds and fisheries share the same fishing resources and grounds, resulting in their inevitable interaction, with significant conservation implications for the firsts. Seabirds scavenging on fishery waste modify their foraging ecology, behaviour and diet with potential consequences on their health. In addition, these interactions often result in the incidental capture of seabirds by fisheries, known as bycatch and thought to drive the decline of a hundred seabird species. While the dynamics of seabird- fishery interactions have been assessed through onboard observations and, more recently, by using tracking technologies at large spatiotemporal scales, studies at fine spatiotemporal scales are still scarce and with uneven results. This thesis aims to enhance the understanding of the dynamics of seabird-fishing interactions with industrial fisheries, with two parallel objectives: (1) unravel fine-scale seabird-fishery dynamics by identifying which, where and when seabird species interact with specific fisheries, uncovering the drivers behind these dynamics, and assessing the legal and political status of the fisheries involved; (2) explore methods for examining seabird-fishery interactions when vessel tracking is unavailable, which is often difficult to obtain and may have gaps due to faulty equipment, illicit manipulation (e.g., Illegal, Unreported, and Unregulated fishing activity; IUU), or lack of adoption in some fleets. To pursue these objectives, we generally used bird-borne GPS data and, in some specific cases, in combination with accelerometers, wet-dry, pressure and radar detectors sensors (capable of scanning seabird surroundings to identify vessels) and coupled it with gridded or raw Automatic Identification System (AIS) data from vessels. The thesis focused on NW Africa and the NW Mediterranean regions. The first is recognised as one of the most important seabird hotspots and upwelling systems worldwide, with intensive fishing activity and a significant presence of IUU fishing. The second holds high marine traffic activity by fishing, merchant, and recreational vessels. Unlike western Africa, where seabird-fishing interactions are poorly studied, it is well known that in this NW Mediterranean region, bycatch is the primary driver of population decline for endemic sea- bird species. The combination of bird-borne GPS and AIS data showed only three out of the nine seabird species in NW Africa, and the only species examined in NW Mediterranean frequently attended industrial fishing vessels: Cory’s shearwaters (Calonectris borealis), Cape Verde shearwaters (Calonectris edwardsii), Audouin’s gulls (Ichthyaetus audouinii) in NW African waters, and Scopoli’s shear- waters (Calonectris diomedea) in NW Mediterranean. All of them primarily attended trawlers, indicating these species feed on fishing discards but are also at risk of bycatch. The drivers of seabird-fishery interactions encompassed environmental factors (e.g., coastline distance) and vessel characteristics (e.g., vessel length or gear type). In NW Africa, seabirds traversed boundaries, foraging on up to five Exclusive Economic Zones and interacted with fishing vessels holding flags from 24 countrie By combining GPS, accelerometers, and wet-dry sensors, alongside machine learning techniques, we showed that seabird-vessel interactions can be inferred through movement analysis. In addition, when combined with radar detectors, this method demonstrated effectiveness in monitoring vessel activity when vessel tracking may be lacking. This thesis provided new approaches to the study of the dynamics of seabird-fishery interactions and to monitoring vessel activity through the use of bird-borne technologies. We showed that these approaches can be beneficial when applied to largely understudied regions where onboard observation and fishing surveillance are scarce or when vessel tracking data is unavailable, establishing an evidence-based framework that can help focus conservation efforts.