MEPS 605:49-59 (2018)  -  DOI: https://doi.org/10.3354/meps12757

ABSTRACT: Human fisheries inadvertently attract and provide food for a range of wild organisms worldwide with important ecological consequences. Some animals directly feed on human catch (‘depredators’, e.g. killer whales), causing economical losses and calling for wildlife management. However the impact of depredation (and its potential management) on the behaviour of the other scavengers attracted to vessels (e.g. seabirds) is unknown. We examined how the fine-scale behavioural response of wandering albatrosses to a toothfish longline fleet was influenced by the presence of depredating killer and/or sperm whales. We hypothesized that the presence of depredating whales might facilitate detection of and/or access to food at fishing vessels for surface-feeding albatrosses. We used seabird GPS tracking together with a vessel monitoring system (GPS vessel tracking) coupled with systematic onboard records of depredator numbers during 3 fishing seasons. We found that when albatrosses ‘encountered’ vessels (n = 254), they had the same probability to start attending vessels whether or not cetaceans were present. However, once attracted, they attended the vessel longer when depredators were present. We conclude that birds are attracted to vessels independently of the presence of cetaceans, but that depredating whales probably facilitate access to food for surface-feeding birds such as the wandering albatross. Scavenging behaviour of seabirds does not appear to be strongly dependent on the presence of depredating cetaceans and is likely minimally affected by changes in cetacean behaviour. This type of data is rare and we discuss how these results for wandering albatrosses could be generalized for other seabird species.

KEY WORDS: Fisheries interactions · Seabird foraging · Depredation · Longliners · Trophic interactions · GPS tracking · Sub-Antarctic · Toothed whales