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

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 (+/- 1SD) 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 45 degrees S and 50 degrees S.