UC Santa Cruz

Marine fish population fluctuations are pervasive. A primary driver of marine fish population fluctuation is annual recruitment variability. For over a century, fisheries oceanographers have tried to attribute cause to observed recruitment variability with varying degrees of success. While several hypotheses of recruitment variability can be found in the literature, most can be grouped into either food web- or transport-dependent mechanisms. The mechanistic basis of food web-dependent drivers is that larval survival, and eventual recruitment, is determined by starvation or predation mortality. Transport-dependent drivers are related to advective processes that disperse larvae into or out of habitat favorable for recruitment. In this dissertation I address these two mechanisms of recruitment variability for Shortbelly Rockfish, a highly abundant and ecologically important fish species of the California Current System. In Chapter 1, I develop and apply a bioenergetics growth model to understand how spatial variation in ocean conditions determines growth potential. I find that spatial patterns of early life stage-specific growth potential correspond with important early life history events. In Chapter 2, I introduce interannual variability in ocean conditions to the growth model and find that hotspots of spatial growth potential explain 78.6% of Shortbelly recruitment variability. This result supports the hypothesis that food web-dependent processes are important for recruitment strength. In Chapter 3, I introduce transport-dependent processes to the model framework and find that the relative importance of food limitation and transport on recruitment are dependent on interannual climate cycles (El Niño Southern Oscillation). The preponderance of recruitment drivers being context dependent amongst a backdrop of differing climate conditions may explain why understanding recruitment mechanisms has been so challenging.