Fish prey of the sympatric Galapagos fur seals and sea lions: seasonal variation and niche separation

Analysis of fish otoliths in scats and vomits of Galapagos fur seals (Arcto cephalus galapagoensis) and Galapagos sea lions (Zalophus californianus wol lebaeki) was used to determine the numerical composition of the diets for t he post-El Nino year 1983, the cold seasons in 1984 and 1985, and the warm season in 1986. Between 84 and 99% of all otoliths in fur seal scats were f rom myctophids and bathylagids. The fur seals' diet included 26 species. On ly 3 species contributed more than 1% of otoliths. No seasonal differences in diet were found. Sea lion samples contained a mean of 14 otoliths. Sardi nes (Sardinops sagax) contributed 75-85% of otoliths. Sea lions preyed on 2 4 species, but only 3 surpassed 1% abundance. Seasonality was not reflected in the sea lions' diet. After the 1982-1983 El Nino, the diets of both spe cies deviated from those in all other years of the study. Food-niche overla p between the two sympatric species was almost non-existent. This is hard t o understand, based on our knowledge of the diving capabilities of the two species, but reflects the fact that Galapagos fur seals are nighttime forag ers and sea lions are daytime foragers.