UPPER TROPHIC LEVEL PREDATORS INDICATE INTERANNUAL NEGATIVE AND POSITIVE ANOMALIES IN THE CALIFORNIA CURRENT FOOD-WEB

We used a 21 yr time series of productivity for 6 seabird species nest ing in large numbers at the Farallon Islands, 40 km offshore of San Fr ancisco, California, USA, to assess proximate and remote factors leadi ng to variation in the food supplies available to these predators. The latter sampled prey throughout a 3200 km(2) area. Depending on foragi ng ecology and reproductive capacity, some species were more sensitive to food web perturbation than others. A serious lack of food was indi cated by negative reproductive anomalies during all warm-water events, some of which were classified as tropical El Nino and others which we re not. Equally spectacular but positive anomalies occurred during yea rs adjacent to the negative ones, particularly evident among the most sensitive species. Much of the annual variation, positive or negative, in seabird reproductive success was explained by variation in the Sou thern Oscillation and/or the Aleutian low pressure system, both of whi ch affect sea-surface temperature and thermocline depth off California . Results indicate that perturbations in the marine food web of the Ca lifornia eastern boundary current system, as indicated by the availabi lity of food to seabirds, are much more complex than is generally appr eciated, and are not confined only to negative excursions from normalc y. ENSO is important, but other global atmosphere-ocean phenomena affe ct the California Current just as dramatically.