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Abstract
Human fishing activities are negatively altering marine ecosystems in many ways [1,
2], but scavenging animals such as seabirds are taking advantage of such activities
by exploiting fishery discards [3-5]. Despite the well-known impact of fisheries on
seabird population dynamics [6-10], little is known about how discard availability
affects seabird movement patterns. Using scenarios with and without trawling activity,
we present evidence that fisheries modify the natural way in which two Mediterranean
seabirds explore the seascape to look for resources during the breeding season. Based
on satellite tracking data and a mathematical framework to quantify anomalous diffusion
phenomena, we show how the interplay between traveling distances and pause periods
contributes to the spatial spreading of the seabirds at regional scales (i.e., 10-250
km). When trawlers operate, seabirds show exponentially distributed traveling distances
and a strong site fidelity to certain foraging areas, the whole foraging process being
subdiffusive. In the absence of trawling activity, the site fidelity increases, but
the whole movement pattern appears dominated by rare but very large traveling distances,
making foraging a superdiffusive process. Our results demonstrate human involvement
on landscape-level behavioral ecology and provide a new ecosystemic approach in the
study of fishery-seabird interactions.