THE INFLUENCE OF COMMERCIAL FISHERIES IN DAILY ACTIVITY OF AUDOUINS GULL LARUS-AUDOUINII IN THE EBRO DELTA, NE SPAIN

The arrivals and departures of Audouin's Gulls Larus audouinii from th e breeding colony in different commercial fishery situations were stud ied 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 wheth er 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 we re probably related to nocturnal foraging activity, and suggested that this nocturnal activity occurred under any fishing fleet activity sit uation. When trawlers did not operate. diurnal activity wan also recor ded probably associated with foraging trips to rice fields. Any change s in fishery activity, such as the trawler moratorium established in 1 991 during the breeding season of Audouin's Gull may affect the feedin g ecology of the species and its conservation.