Nonstationary Productivity in Global Fish Stocks
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Environmental change in the ocean has raised significant concern over the continued productivity of global fisheries resources. In this thesis, I investigate time-varying rates of population growth and biomass production (i.e. `nonstationary productivity') in global fish stocks by analyzing a new global database of fisheries time series. Using Bayesian population models, I describe nonstationary productivity in individual stocks, and then synthesize results at regional, taxonomic, and global scales. I demonstrate significant regional and global trends in two aspects of stock productivity: juvenile recruitment (the production of individual fish) and total productivity (the production of stock biomass). Importantly, these declines can be explained by changes in temperature, phytoplankton, and the intensity of historical overfishing. Further, observed trends are shown to significantly alter rebuilding timelines for depleted stocks. These results help track the historical trends and current status of stock productivity and reveal key environmental drivers at the regional and global scale.