Year-round distribution of white-chinned petrels from South Georgia: relationships with oceanography and fisheries
The white-chinned petrel Procellaria aequinoctialis is a medium-sized procellariiform with a circumpolar subAntarctic breeding distribution. Feeding during both day and night, and often competing aggressively for bait, offal and discards, it has the highest incidental mortality rate of any seabird in Southern Ocean longline fisheries. Although still abundant, the limited census data suggest rapid population declines. Using geolocators, the movements of 10 white-chinned petrels from South Georgia were tracked for 226–664 days, which in combination with previous satellite-tracking provided the first comprehensive description of migration routes and year-round distribution of this species from any site. All birds migrated to Patagonian Shelf and shelf-break waters, concentrating in highly productive areas east of the River Plate estuary and to a lesser extent on the open shelf off central Argentina. Two birds traveled initially to the southern Patagonian Shelf but then moved in mid-winter to the Humboldt Current (Chile), before returning directly to South Georgia. One bird adopted this strategy in two winters, and was consistent in timing of return migration to South Georgia, but not of arrival off Chile. Despite the distance (>2000 km), birds returned to feeding sites on the Patagonian Shelf for all pre-laying exodus, and most incubation, trips. In contrast, most chick-rearing trips were to the local shelf, central Scotia Sea or South Orkney Islands, on average only 610 km from the colony. The distribution of white-chinned petrels overlapped with several major fisheries, many of which are known or suspected to have high rates of seabird bycatch. Until this issue is addressed, the status of the white-chinned petrel population at South Georgia should be viewed with considerable concern.
Authors: Phillips, Richard A., Silk, Janet R.D., Croxall, John P., Afanasyev, Vsevolod