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

Abstract

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.

Resumo

Se estudió la utilización de cangrejales y áreas de pesca por la Gaviota de Olrog durante el periodo no reproductivo. Durante los aãos 2004 y 2005 se realizaron censos en diferentes áreas de la Laguna Costera Mar Chiquita y el Puerto Mar del Plata, Provincia de Buenos Aires, Argentina. En ambos sitios de estudio el mayor número de individuos se observó entre los meses de junio y agosto. Adicionalmente entre los meses de abril y agosto de 2005 se estudiaron los movimientos de cinco individuos no reproductores mediante el uso de radio-transmisores. De un total de 407 muestras se obtuvieron 278 localizaciones. Todos los individuos instrumentados mostraron una alta fidelidad al sitio. El 96% de las localizaciones se registraron en cercanías de la desembocadura de la laguna, asociadas a cangrejales y areas de pesca deportiva. Considerando el estatus de conservación de la Gaviota de Olrog (‘Vulnerable’) y los efectos negativos de su interacción con la pesca deportiva, programas de conservación en áreas no reproductivas deben ser implementados.