Looking for trawlers: the new seabird’s lifestyle

Fisheries can affect seabird movements and behaviour. This
is the result of a recent study conducted in the Balearic islands, south of Spain.

Researchers analysed and modelled satellite tracking data of 10 foraging trips of breeding Balearic shearwaters (Puffinus mauretanicus) and 26 trips of breeding Cory’s shearwaters (Calonectris diomedea). By relating the birds movements with trawling activities, an interesting link was found.

When trawlers were active, the birds tended to concentrate in certain high-resource density area where the fishing boats were operating. When trawlers were inactive - during weekends, holidays or trawling moratorium days - the birds engaged in more widely spread and long flights.

Birds were probably attracted to the fish discarded by trawlers, as this represents an easy meal which does not require spending too much time and energy. Availability of discards may improve the breeding performance of Mediterranean seabirds but it may also decrease their fidelity to certain areas.

It’s unclear whether this may be good or bad for the birds in the long run, but it’s obvious how human activities are continuously impacting on nature.

SB

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Photo:
trawler and pelagic seabirds http://www.twooceanssportfishing.com/pelagic-birding

For more information:
http://www.cell.com/current-biology/abstract/S0960-9822(09)02160-5

Bartumeus F., Giuggioli L., Louzao M., Bretagnolle V., Oro D., Levin S.A. 2010. Fishery discards impact on seabird movement patterns at regional scales. Current Biology 20:215–222.
Summary - Human fishing activities are negatively altering marine ecosystems in many ways, but scavenging animals such as seabirds are taking advantage of such activities by exploiting fishery discards. Despite the well-known impact of fisheries on seabird population dynamics, 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.