Linking Otoliths and Oceanography: Environment-Growth Relationships for Early Life History Stages of Rockfishes off Central California

Recruitment strength in most marine fishes is strongly influenced by environmental conditions encountered during early life history (ELH), which has motivated research to develop recruitment indices based on environmental predictors of larval growth and survival. In this study, we quantify variability in growth during early life history for several species of rockfish, and develop quantitative models relating inferred growth rates to measures of physical forcing which serve as a proxy of environmental conditions experienced by individual fish.  Individual growth trajectories are based on micro-increment analysis of sagittal otoliths from over 500 individual rockfish captured as pelagic juveniles off central California from 1983 to 2008.  We link observed growth patterns to time series of environmental variables using a simulation-based state-space model that explicitly accommodates changes in growth patterns related to developmental stage and autocorrelation in growth rate within individual fish.  Initial analysis of otolith growth patterns indicates that sensitivity to environmental conditions is consistently highest between ages roughly corresponding to exhaustion of maternal provisions and the development of robust foraging capabilities and lipid reserves.  Our analysis also evaluates whether proxies of local environmental condition (e.g.wind forcing, coastal upwelling and downwelling, sea surface temperature, and sea level anomaly) have instantaneous, lagged or cumulative effects on individuals’ growth rates, and whether cumulative variability of environmental parameters better explain variability in ELH growth rates.  Results from this work represent a significant advance over previous analyses of environment-growth relationships in rockfishes, and in particular, partition the contribution of extrinsic processes (e.g., food web responses to cumulative environmental forcing) and intrinsic state (energy reserves, size, and foraging history) to observed autocorrelation in otolith growth rates.  We also compare our results to simulations of the coastal plankton ecosystem off central California derived from a simple coupled bio-physical model which provides a regional comparison of the integrated effects of environmental variability on ecosystem productivity.  Moreover, assuming that conditions favoring larval growth translate into increased survival, our results provide a basis for environment-recruitment indices that may reduce uncertainty and improve performance of existing stock assessment frameworks, while also providing insight to mechanisms central to how rockfish populations will respond to climate change.