Effects of the El Niño 1982–83 on California Sea Lions in Mexico

Abstract

Before, during, and after El Niño (EN) 1982–83, several aspects of California sea lion biology were being studied in the Gulf of California (Sea of Cortéz) and the Pacific coast of Baja California, Mexico, as part of a long-term program initiated by representatives of Centro de Investigaciones Biológicas in 1978 (Aurioles et al. 1983; Le Boeuf et al. 1983; Aurioles and Sinsel 1988). The program involved monitoring the population distribution and abundance, estimating annual pup mortality rates, and estimating winter immigration rates of subadult males at major rookeries and resting sites. During winter, a large number of subadult males move into rookeries and resting sites on both coasts of the southern Baja California peninsula (Aurioles et al. 1983). These movements may be analogous to the northward movements of sea lions inhabiting southern California waters (Fry 1939; Mate 1975) which are associated with fluctuations in the distribution of Pacific hake (Merluccius productus; Ainley et al. 1982). Subadult males from the central Gulf may follow the southward fall-winter migration of the Monterey sardine (Sardinops sagax), the threadfin herrings (Ophistonema libertate, O. bulleri, and O. medirastre) and the mackerel (Scomber japonicus) which are the basis for sardine fishery in the Gulf (Aurioles, in press).