Factors of bycatch of birds and mammals in Danish gillnets

Incidental captures (bycatch) in fishing gears exert an important pressure on some fragile populations of megafauna species worldwide. Solutions to reduce or mitigate bycatches of endangered, threatened, and protected species (ETP) exist but are not widely applicable across species and across fisheries. Because of the inadequate monitoring effort in many fisheries, a precise knowledge of the ecological and operational drivers of bycatch is often missing. Here, we exploit 15 years of electronic monitoring (EM) data from the Danish gillnet fishery to dig out the most influential determinants of ETP species bycatch for several species of marine mammals and seabirds subjected to bycatch in our seas. We use a generalised linear mixed model (GLMM) to improve our understanding of the mechanistic relations that exist between observed bycatch rates, and operational and ecological factors in gillnet fisheries. Within the parameters considered in our analysis, we show that some factors are more influential than others to explain species-specific bycatch rates. These results are important for fisheries and conservation managers to design effective and appropriate mitigation measures and ensure the sustainability of the ETP species populations affected by bycatch in gillnets.