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 rockfishSebastesspp. from 1975–2002 in the central California Current by examining the diet of a local marine bird, the common murreUria aalge, on multiple temporal scales. Responses to higher-frequency climate change (interannual El Niño and La Niña 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.