Rockfish response to low-frequency ocean climate change as revealed by the diet of a marine bird over multiple time scales

We examined the effects of ocean climate variability on juvenile rockfish Sebastes spp. from 1975-2002 in the central California Current by examining the diet of a local marine bird, the common murre Uria aalge, on multiple temporal scales. Responses to higher-frequency climate change (interannual El Nino and La Nina events) were strong, with declines in rockfish take in warm-water years. Responses to low-frequency climate events (e.g. shifts of the Pacific Decadal Oscillation, PDO) were less obvious. Inter-annual patterns showed no response to the 1976-1977 regime shift to warmer PDO conditions. Instead, rockfish use declined beginning in 1989, corresponding to another suggested regime change, then rebounded shortly after the hypothesized return to a cool phase of the PDO in the late 1990s. Intra-annual diet patterns, however, revealed changes in rockfish use well before 1989. These signals indicate that declines may have corresponded to the 1976-1977 regime shift but were lagged, possibly due to the long lifespan and intermittent recruitment of rockfish. This interpretation is supported by local upwelling patterns that show a lagged correlation between upwelling and juvenile rockfish abundance in the marine bird diet.