Use of natural and anthropogenic resources by Olrog's Gull Larus atlanticus:: implications for the conservation of the species in non-breeding habitats

We studied the exploitation of crab-beds and fishing grounds by Olrog's Gulls Larus atlanticus in non-breeding areas along the coast of Buenos Aires province, Argentina. During 2004 and 2005, censuses were performed in different areas of Mar Chiquita coastal lagoon and Mar del Plata harbour. Additionally, from April to August 2005 the movements of five non-breeding individuals were studied by means of radio-telemetry. At both study sites the highest numbers of Olrog's Gulls were observed between June and August. A total of 278 radio-tracked locations (from 407 samples) were registered. All the tracked individuals showed strong site fidelity, with 96% of the radio signals registered in the vicinity of the lagoon's mouth, associated with both crab-beds and areas where sport-fishing activities took place. Conservation issues in non-breeding areas should be tackled in the near future, given the conservation status of this species (Vulnerable) and the fact that each year several Olrog's Gulls are being killed because of their interaction with sport-fishing activities.