Decadal increase in vessel interactions by a scavenging pelagic seabird across the North Atlantic

Abstract

Fisheries waste is used by many seabirds as a supplementary source of food,¹ but interacting with fishing vessels to obtain this resource puts birds at risk of entanglement in fishing gear and mortality.² As a result, bycatch is one of the leading contributors to seabird decline worldwide,³ and this risk may increase over time as birds increasingly associate fishing vessels with food. Light-level geolocators mounted on seabirds can detect light emitted from vessels at night year-round.⁴ We used a 16-year time series of geolocator data from 296 northern fulmars (Fulmarus glacialis) breeding at temperate and arctic colonies to investigate trends of nocturnal vessel interactions in this scavenging pelagic seabird. Vessel attendance has progressively increased over the study period despite no corresponding increase in the number of vessels or availability of discards over the same time frame. Fulmars are highly mobile generalist surface feeders,⁵ so this may signal a reduction in available prey biomass in the upper water column, leading to increased reliance on anthropogenic food subsidies⁶ and increased risk of bycatch mortality in already threatened seabird populations. Individuals were consistent in the extent to which they interacted with vessels, as shown in other species,⁷ suggesting that population-level increases may be due to a higher proportion of fulmars following vessels rather than changes at an individual level. Higher encounter rates were correlated with lower time spent foraging and a geographically restricted overwintering distribution, suggesting an energetic advantage for these scavenging strategists compared with foraging for natural prey.

Keywords: Fulmarus glacialis; biologging; bycatch risk; discards; ecosystem effects; fisheries interactions; migration strategies; northern fulmar; prey reduction; seabird behavior.