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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13549

Low spatial overlap between foraging shearwaters during the breeding season and industrial fisheries off the west coast of Portugal

Jorge M. Pereira*, Jaime A. Ramos, Ana M. Marques, Filipe R. Ceia, Lucas Kr├╝ger, Stephen C. Votier, Vitor H. Paiva

*Corresponding author:

ABSTRACT: Fisheries have impacted seabird populations worldwide, either via bycatch mortality or resource depletion. Understanding the overlap between seabird distribution and fisheries is an important element for bycatch risk assessment, though the drivers of variation are not well understood for some seabird populations. Here, we quantified the spatial overlap between foraging Cory’s shearwaters Calonectris borealis during the breeding season and commercial fisheries operating within the Portuguese Exclusive Economic Zone. In addition, we evaluated whether the overlap varied as a function of boldness, sex and breeding stage. For this, we GPS-tracked 361 foraging trips from 72 shearwaters nesting at Berlenga Island, Portugal over five consecutive breeding seasons (2012–2016). Simultaneously, we used fishing effort from Global Fishing Watch detailing the distribution of industrial fisheries within the temporal and spatial range of shearwaters’ tracking. Despite fishing vessels were present during 88.1% of foraging trips, shearwaters spent only on average 13.3% of the time foraging in the same areas as fisheries. Such low spatial overlap is likely driven by high prey availability near the colony and suggests reduced direct competition for fishery-related resources. We also found variations in the overlap with fisheries along the breeding period, with shearwaters spending approximately 11% more time foraging in the same areas as fixed gear and purse seine vessels during pre-laying than during chick-rearing. Surprisingly, no sex or boldness-related differences were found in the overlap with any fishing gear. Our findings have implications for understanding within population variations in the overlap between fisheries and seabirds and in-turn bycatch risk.