Assessing seabird bycatch in gillnet fisheries using electronic monitoring

The unintentional capture (bycatch) of seabirds in gillnet fisheries kills hundreds of thousands of individuals annually and is thought to threaten the conservation of entire populations. However, data from commercial fisheries is often lacking to confirm these suspicions. In Denmark, sparse or incomplete catch data from small-scale gillnetters prevent managers from gaining a comprehensive overview of the importance of seabird bycatch in coastal waters. In this study, electronic monitoring (EM) with video is used to identify and quantify seabird bycatch in a Danish coastal gillnet fishery. Three gillnetters were monitored over a period of 9 years, resulting in 2118 fishing trips and 10,964 hauls; 700 birds from six families were identified. Three species composed >90% of the incidental captures, the common eider (Somateria mollissima), the great cormorant (Phalacrocorax carbo) and the common guillemot (Uria aalge), respectively qualifying regionally as endangered, least concerned and near threatened. There was a clear species-specific spatial and seasonal variability in bycatch per unit effort (BPUE) estimates, highlighting areas of high risk of seabird bycatch. Approximately 40% of all bycatch events were observed in 0.2% of the hauls, suggesting that the full fishing activity should be analysed to obtain accurate seabird bycatch estimates.