California sea lions (Zalophus californianus californianus) have lower chlorinated hydrocarbon contents in northern Baja California, México, than in California, USA

Chlorinated hydrocarbons (CHs) were determined in blubber samples of 18 California sea lions (Zalophus californianus californianus) that stranded dead along Todos Santos Bay, Ensenada, Baja California, México, January 2000–November 2001. ∑DDTs were the dominant group (geometric mean 3.8 μg/g lipid weight), followed by polychlorinated biphenyls (∑PCBs, 2.96 μg/g), chlordanes (0.12 μg/g) and hexachlorocyclohexanes (0.06 μg/g). The ∑DDTs/∑PCBs ratio was 1.3. We found CH levels more than one order of magnitude lower than those reported for California sea lion samples collected along the California coast, USA, during the same period as our study. This sharp north–south gradient suggests that Z. californianus stranded in Ensenada (most of them males) would probably have foraged during the summer near rookeries 500–1000 km south of Ensenada and the rest of the year migrate northwards, foraging along the Baja California peninsula, including Ensenada, and probably farther north.