Seabird behaviour influenced by fishing vessels

A team of scientists led by the University of Exeter tracked the movement and behaviour of seabirds using GPS devices, and discovered that northern gannets change their behaviour in response to the presence of large vessels such as trawlers, suggesting each boat can significantly influence the distribution and foraging patterns of these and other marine predators.

Northern gannets are known to feed on discards from fishing vessels as well as diving for fish, and their population has been steadily increasing for decades. Studies have confirmed their use of fisheries waste by showing that the birds are eating fish that have come from far deeper than they are able to dive.

Scientists analysed GPS tracking data from 74 gannets from six breeding colonies around Ireland, and combined these with similar GPS tracking data from fishing vessels.

The information gathered revealed that gannet behaviour is influenced by fishing vessels at distances of up to 11km – the first estimate of the distance at which vessels start to affect these birds' behaviour.

Dr Thomas Bodey of the University of Exeter, who led the study, said: "Our work suggests each fishing vessel has a substantial footprint, with the behaviour of seabirds affected within a 22km diameter circle surrounding it, much larger than we expected."

By studying bird-boat interactions, the team also discovered that individual gannets can adjust their behaviour depending on whether the vessel is actively fishing or not, and also based on the type of fishing gear carried.

The findings help to understand the spatial influence of fisheries, which is critical to marine planning and policy – including shipping, offshore development, bycatch and fisheries themselves.