Spatio-temporal variation in mortality rates of White-chinned Petrels Procellaria aequinoctialis interacting with longliners in the south-west Atlantic

Abstract

The White-chinned Petrel Procellaria aequinoctialis is the second most commonly captured species by Argentinean longliners. The severe declines that this species has experienced in some of its populations (e.g. South Georgia Islands) have been principally attributed to incidental mortality associated with longliners. In this study we analyse the spatio-temporal variability in the mortality rates of White-chinned Petrels on the Patagonian Shelf and the effects that environmental and operational variability have on such mortality. The average capture rate (¡ 1 SD) for the period 1999–2003 was 0.014 ¡ 0.090 White-chinned Petrels for every 1,000 hooks deployed. Higher capture rates were observed when short longlines were deployed. Capture rates were not affected by the wind speed or by the time to the full moon. The distribution of the captures differed throughout the year. During autumn–winter most captures took place in the north of the Patagonian Shelf, whereas during spring–summer incidental captures occurred principally to the south between 45uS and 50uS.El Petrel Barba Blanca Procellaria aequinoctialis constituye la segunda especie ma´s frecuentemente capturada por la flota palangrera Argentina. Los importantes decrecimientos poblacionales observados en algunas poblaciones de esta especie (e.g. Islas Georgias del Sur) han sido principalmente atribuidos a la mortalidad incidental asociada a embarcaciones palangreras. En este trabajo se analizo´ la variacio´n espacio- temporal en las tasas de captura incidental del Petrel Barba Blanca a lo largo de la Plataforma Continental Argentina y se estudio´ el efecto que diferentes variables ambientales y operacionales tienen sobre la mortalidad incidental de esta especie. La tasa de captura promedio (¡ d.s) durante el periodo 1999–2003 fue de 0.014 ¡ 0.090 Petreles Barba Blanca cada 1.000 anzuelos. Mayores tasas de captura fueron registradas al utilizar palangres cortos. No se observo´ un efecto de la intensidad del viento ni de la distancia a la luna llena sobre las tasas de captura. La distribucio´n de las capturas difirio´ a lo largo del an˜ o. Durante el oton˜ o-invierno la mayorı´a de las capturas estuvieron localizadas al norte de la Plataforma Continental Argentina, mientras que durante los meses de primavera-verano las capturas estuvieron localizadas principalmente entre los 45uS y 50uS.