Replicate springtime (May - June) vessel-based surveys in the western Mediterranean during standardized trawl surveys of the Spanish continental shelf and slope over three years (1999, 2000, 2002), provide broad-scale information on seabird distributions from the Strait of Gibraltar to Cape Creus. All observations were made by the same observer (Jose Maria Arcos) during 1999, 2000, and 2002 using standardized strip-transect techniques (Tasker et al. 1984) with specific adaptations to the study area. A 300 m strip-width transect band was used, counting at both sides of the vessel (i.e., surveying a 600 m band) when the conditions (light and wind) were appropriate. Snap-shot counts for flying birds were used. All birds observed during the surveys were recorded and aggregated into 10-minute bins. To study the distribution and oceanographic habitat of seabirds in the Western Mediterranean during the spring (May - June) of multiple years. Surveys were conducted onboard B/O Cornide de Saavedra research vessel, as part of the annual MEDITS trawl surveys, extending along the Mediterranean coast of the Iberian Peninsula, from the Strait of Gibraltar in the southwest to Cape Creus in the northeast. Maite Louzao processed the at-sea data, as part of her Ph.D. dissertation, in the laboratory of Dr. Daniel Oro, at the Mediterranean Institute for Advanced Studies (IMEDEA), in Mallorca, Spain.