Reconstructing the population dynamics of southern California Paralabrax spp. in the face of a changing ocean

Fishery managers are tasked with preparing our fisheries for climate change, but doing so requires data to assess population status and environmental drivers, both of which are typically limited. Many small-scale fisheries, like recreational-only fisheries, have a paucity of information and resources to perform robust assessments, which results in data-limited management measures that can inadvertently increase the vulnerability of the resource to detrimental harvest and climate change impacts. Here I focus on the popular and overexploited southern California recreational saltwater bass fishery, which despite its economic and cultural significance to the state, lacks long-term species-specific data and formal population assessments. By leveraging a variety of disparate data sets, taxonomy methods, and advanced quantitative methods, I reconstruct the population dynamics of the two focal species, Barred Sand Bass (Paralabrax nebulifer) and Kelp Bass (P. clathratus), over most of the last century and across rapidly changing ocean conditions. I begin with Barred Sand Bass and build a bespoke Bayesian capture-mark-reencounter model to estimate demographic rates over three historical periods spanning 54 years. Using these rates, I generate, for the first time, estimates of abundance, and along with other data sources (juvenile recruitment, adult densities, harvest, and sea surface temperature) and historical accounts in the literature, I demonstrate how the environment and harvest have contributed to long-term fluctuations in productivity. I then develop a robust method to construct and validate a taxonomic key for distinguishing southern California Paralabrax spp. larvae and use this key to unlock a larval abundance data set with high spatial and temporal resolution. Using these larval data within a geostatistical modeling framework, I generate species-specific standardized indices of larval abundance, quantify the influence of environmental covariates on their long-term spatiotemporal patterns, and explore the predictive power of the larval time series to anticipate future catches. Based on these modeling efforts, I contribute improved fishery management tools for monitoring status and trends and demonstrate species-specific population dynamics, highlighting the species’ different susceptibilities to harvest and climate change impacts. Taken together, these studies pave the way toward an ecosystem and climate-ready approach to fisheries management for this important group of fishes