Although most think of the California sea lion, Zalophus califorianus, as the delightful circus animal balancing a ball on its nose, many dislike these abundant mammals for eating their fish and messing up docks. The United States stock of California sea lions has experienced an annual average growth rate of 6.2% since 1983 (Carretta et al. 2000). Currently, the NOAA - Fisheries divides the California sea lion population into three stocks (United States, western Baja California, and Gulf of California) based on the location of major rookeries and the international border. Our research is designed to improve stock definition of within the species using molecular markers.
Sea lion studies are a collaborative effort involving samples from the major rookeries in the Channel Islands collected by Mark Lowry of the Coastal Marine Mammal Program, samples from rookeries along the Baja California coast and Gulf of California collected by Yolanda Schramm Urrutia (Universidad de Baja California) and samples collected from Z. wollebaeki in the Galapagos Islands by Daniel Palacios and Heidi Snell (Pacific Grove lab, SWFSC, and Charles Darwin Research Station, in the Galapagos Islands, Ecuador).
Our most recent knowledge of genetic subdivision within the species is based on the PhD dissertation of Yolanda Schramm Urrutia (2001). Results support the identification of two clades, corresponding to Z. californianus and Z. wollebaeki and show strong phylogeographic signal within Z. californianus. Interestingly, haplotypes from the outgroups and from the Galapagos islands are connected to California sea lion haplotypes through haplotypes found in the central and northern Gulf of California. A number of unique haplotypes were found only in the upper Gulf of California. These data are consistent with results based on morphological data in which it was found that skulls collected in the Galapagos and Gulf of California share primitive characters and that skulls from the Pacific coast show derived characters (Aurioles et al., 2000). Lastly, we found statistically significant population structure throughout the range of the species suggesting four demographically distinct areas: "Pacific", "southern Gulf of California", "central Gulf of California" and "northern Gulf of California". We are currently investigating patterns of population structure among the Pacific coast rookeries. The large number of samples collected from the southern California rookeries also provides the opportunity to look at haplotype diversity as a function of sample size and of rookery size, thus refining our ability to assess the use of genetic markers to estimate stock boundaries. These studies are on-going.
Aurioles G., D., S. Castillo F., I. Contreras A., and L.G. Barnes. 2000. Latitudinal patterns in tooth characters of the North American California sea lion population (Zalophus californianus californianus). Abstract. XXV ReuniA?n Internacional para el Estudio de los MamAferos Marinos. La Paz, B.C.S., May 7-11. 77 pp.
Carretta, J., K. Forney, M. Muto, J. Barlow, J. Baker, B. Hanson, and M. Lowry. 2004. US Marine Mammal Stock Assessments: 2004. NOAA-TM-NMFS-SWFSC-375.
Schramm Urrutia, Y. 2002. Genetic Structure and Phylogeography of California Sea Lions (Zalophus californianus californianus ) along the Baja California Peninsula, Mexico. PhD Dissertation. Universidad de Baja Califrornia.