The influence of commercial fisheries in daily activity of Audouin's Gulls Larus audouinii in the Ebro Delta, NE Spain

Abstract

The arrivals and departures of Audouin's Gulls Larus audouinii from the breeding colony in different commercial fishery situations were studied to assess changes in their daily activity pattern. Gulls arriving to the colony were assumed to show arrivals from the foraging grounds, while those departing from the colony were assumed to show departures to forage . The activity pattern of Audouin's Gulls in the Ebro Delta seemed to depend especially on trawler activity, irrespective of whether night fisheries occurred at the same time. Indeed, gulls seemed to fit their arrivals and departures to the trawler timetable. Audouin's Gull departures from the colony at sunset were always recorded, those being most intense when only night fishing occurred and slightly lower when no fishing vessels were working in the area . These departures were probably related to nocturnal foraging activity, and suggested that this nocturnal activity occurred under any fishing fleet activity situation. When trawlers did not operate, diurnal activity was also recorded, probably associated with foraging trips to rice fields . Any changes in fishery activity, such as the trawler moratorium established in 1991 during the breeding season of Audouin's Gull may affect the feeding ecology of the species and its conservation .