Seabirds, set-nets, and conservation management: assessment of conflict potential and vulnerability of birds to bycatch in gillnets

We addressed the issue of bird bycatch in set-nets in the southern Baltic Sea by (i) assessing the vulnerability of diving birds to drowning by developing a vulnerability index based on weighted bird abundance, (ii) providing information on set-net fishing activities, and (iii) using a spatial overlap approach to indicate the potential conflicts between diving birds and fishing activities. Birds and fisheries concentrated in the same areas. Vulnerability and potential conflict were highest during winter and spring in coastal waters and around shallow offshore grounds. Local bycatch studies validated the usefulness of our approach, which can provide a valuable tool for conservation purposes. Although the conflict analysis outlined the current extent of overlap between birds and fisheries, the vulnerability index indicated important areas and periods in terms of diving bird abundance, irrespective of fisheries, and enabled the development of appropriate conservation and management options. A suite of measures including temporal or spatial restrictions can be derived, despite a scarcity of real data for bycatch rates. This approach is particularly useful for assessing impacts that are difficult to monitor and where mortality cannot be properly addressed, as in artisanal gillnet fisheries. It is also generally applicable to any marine area or species worldwide.