Changes in California sea lion diet during a period of substantial climate variability

Abstract

The California Current Ecosystem (CCE) is a productive eastern boundary upwelling system that supports a wide variety of forage stocks. Decadal and interannual variability in the environment influence forage species, which in turn affects predators. The recent diet of California sea lions (Zalophus californianus; CSL) from Central California was determined using identification of hard parts from scat samples (n = 785) collected on Ano Nuevo Island (37.1083°N 122.3378°W) in 2010 and 2012–2016. Comparisons were made with previously reported data from the late 1990’s and with prey availability as measured by fishery-independent surveys. A significant shift in diet was seen between the two decades where diet from the 1990’s was dominated by Pacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax). By 2010, diet was more diverse, characterized by rockfishes, Pacific hake, and market squid. There were also strong interannual differences in diet during the most recent decade, a time of substantial climate variability in the North Pacific Ocean. In general, prey were consumed in relation to what was available in the environment.