Skull Morphology of California and Steller Sea Lions in the Pacific Northwest: Evidence for Potential Hybridization

ABSTRACT Eumetopias jubatus (Steller sea lions) that breed on the Oregon coast are generally smaller than those found in Alaska. During the breeding season, male Zalophus californianus (California sea lions) move past E. jubatus rookeries in Oregon on their way to breeding rookeries in Southern California. Introgression by male Z. californianus could potentially explain the difference in size of Oregon E. jubatus relative to other E. jubatus populations. To assess whether morphologically detectable hybrids occur between Z. californianus and E. jubatus in Oregon, we used traditional skull morphometrics and Principal Component Analysis to identify individuals with intermediate morphological characteristics. Multiple range comparisons were used to determine which groups differed significantly. The comparisons revealed significant cranial morphological variation within each species' clusters and identified two male Z. californianus that overlapped with the male E. jubatus cluster, as well as two female E. jubatus that overlapped with the male Z. californianus cluster, suggesting potential hybrid status. These results support the possibility that long‐term introgression between these two species may account for the observed size difference of the Oregon and Alaskan E. jubatus .