ships or aircraft, weather conditions and availability of observers. The Marine IBA LIFE Project based its marine surveys on a modified version of Tasker's et al. (1984) methodology, recommended by the European Seabirds at Sea Group (Camphuysen & Garthe, 2004). Data are collected in transects defined by a period of time (normally 5 to 10 minutes) and 2 are expressed in density (birds/km ). All birds in contact with the water inside the pre-defined transect are counted. Birds in flight are counted by 11 carrying out regular snapshots , so as not to over-estimate the density. In addition, data from bird sightings carried out by the Program for Observation of Fisheries in the Azores (POPA) were also used. These are based on counts carried out at regular intervals. In order to make proper use of the ESAS methodology, the presence of the seabirds must not be influenced by the presence of the observer's vessel. Therefore, the use of fishing boats must be avoided, as they attract some species of bird due to discarded fish. In spite of the ESAS and POPA data being different (the POPA method is based on point counts and not transects) subsequent analysis was carried out in a similar way, applying the same statistical procedure.
a. ESAS methodology
11
A snapshot is an instant point count of the birds present in a certain area at a given moment. The name snapshot comes from the similarity of this method to taking a photograph of the count area at a precise moment
132
The ESAS methodology was the more widely used and was applied to all surveys carried out on oceanographic and/or marine-tourism ships in the regions of the Azores, Madeira and the Mainland. Information collected was incorporated into an European database in a format pre-defined by the ESAS group. This database was created in the 1980s and gathers data from most marine and airborne surveys carried out in Northeast Europe. Its main advantages are being able to study associations between seabirds and mammals, and the introduction of specific behavioural codes (allowing a more detailed analysis of the data from the point of view of marine IBAs.) This database allows access to records obtained by other researchers and that may be useful for a certain geographical area or ecological study, and not just own data. The ESAS methodology is also used by other countries in Southern Europe, such as Malta, Italy and Greece. Therefore, in future, most surveys carried out in the Mediterranean will be comparable to those carried out in Portugal, which will allow cross-referencing of data and better study of common seabird species. On the mainland, the annual cruises organized by IPIMAR were the main platform used for marine surveys. These surveys were complemented with voyages carried out with other cooperating bodies, such as the Hydrographic Institute or the Small Cetaceans in the European Atlantic and North Sea (SCANSII) project. This was in addition to surveys in the Ria of Aveiro, the Berlengas Archipelago and in the Algarve carried out by the University of Aveiro.
Important Areas for Seabirds in Portugal