AbstractThe distribution of seabirds west of Scotland was studied relative to water masses in August 1988. Surface salinity was used to indicate the ship's position relative to the water masses described in the literature. Comparisons were made between seabird densities in Inshore Water, the Northern Coastal Current, the Southern Coastal Current and Atlantic/Hebridean Water.Seabird density varied with water mass; some species distributions suggested strong habitat associations. Water masses represent marine habitats, with different physical regimes supporting different marine life; patterns in bird distribution are likely to reflect prey distribution and availability.Manx shearwatersPuffinus puffinus, razorbillsAlca torda, guillemotsUria aalge, and kittiwakesRissa tridactylawere found mostly in Inshore Water, with lower densities in the Northern and Southern Coastal Current water. Only trace numbers of these species occurred in Atlantic/Hebridean Water.Storm petrelsHydrobates pelagicus, fulmarsFulmarus glacialisand puffinsFratercula arcticawere found in very low densities in Inshore Water, and were dispersed in higher densities throughout the more oceanic areas.These data suggest that in late summer the Inshore Water of southwestern Scotland has the highest densities of seabirds potentially vulnerable in the event of an oil incident.