Light-level geolocators reveal spatial variations in interactions between northern fulmars and fisheries

Seabird-fishery interactions are a known and common phenomenon of conservation concern. Here, we highlight how light-level geolocators provide promising opportunities to study these interactions. By examining raw light data, it is possible to detect encounters with artificial lights at night, while conductivity data give insight on seabird behaviour during encounters. We used geolocator data from 336 northern fulmars tracked from 12 colonies in the North-East Atlantic and Barents Sea during the non-breeding season to (1) confirm that detections of artificial lights correspond to encounters with fishing vessels by comparing overlap between fishing effort and both the position of detections and the activity of birds during encounters, (2) assess spatial differences in the number of encounters between wintering areas, and (3) test whether some individuals are more often foraging around fishing vessels than others. 88.1% of the tracks encountered artificial light at least once, with 9.5 ± 0.4 detections on average per 6-month non-breeding season. Encounters occurred more frequently where fishing effort is high, and some colonies had higher probabilities of encountering lights at night. During encounters, fulmars spent more time foraging and less time resting, strongly suggesting that artificial lights reflect the activity of birds around fishing vessels. Inter-individual variability in the probability of encountering light was high (range: 0-68 encounters/6-month), meaning that some individuals were more often associated with fishing vessels than others, independently of their colony of origin. Our study highlights the potential of geolocators to study seabird-fishery interactions at a large scale and a low cost.