Abstract As the western stock of Steller sea lions continues to decline, government managers may place additional controls on commercial fisheries as protective measures. Currently, management decisions regarding rookeries are based largely on the geographic location of a site, and little effort has been made to describe sea lion rookeries in an ecosystem context. We provide a broad ecological characterization of rookeries for the western stock of Steller sea lions, which can be used in making management decisions to facilitate their recovery. We gathered data on habitat (bathymetry, sea surface temperature, substrate type, and orientation), diet and population trends from available literature and National Marine Fisheries Service databases (1990–98), and we used a Geographic Information System to group sea lion rookeries into ecologically related regions. Ecological attributes were assigned to rookeries within a 10-nm radius of land. Regions were determined using cluster analysis. Five distinct classes of rookeries (i.e. potential management regions) were identified based on their relatedness to the ecological factors we defined. Several of the regional breaks occur at major oceanic passes including Amchitka, Samalga, and Unimak Passes and are associated with ocean currents.