Project: Mechanisms for low-frequency variability of forage fish: A comparative analysis of North Pacific sardine systems

The low-frequency variability of small pelagic fish is one of the most emblematic and best-documented cases of fish population fluctuations not explained wholly by fishing effort. Over the last 25 years, diverse observations have been integrated into several hypotheses; however, due to the multi-decadal nature of the variability, hypothesis testing of time series observations has proven difficult. This proposal aims to incorporate state-of-the-art modeling tools to tackle this scientific problem. The modeling will enable the synthesis and extrapolation of the piece-wise process-level data on the physics, lower trophic levels, and fish ecology and behavior that is rapidly accumulating. The models we will use are a well-known physical circulation model (ROMS) already implemented in some of the systems (Curchitser et al. 2005; Veneziani et al. 2008a), a recently developed Nitrogen-Phytoplankton- Zooplankton (NPZ) model (NEMURO; Kishi et al. 2007), and its extension in NEMURO.SAN (Rose et al. 2006) to include individual-based simulation of small pelagic fish populations (sardine and anchovies) and their predators and fishing pressure. Physics to fish to fishers models will be developed for the California Current as part of this project, and for the Oyashio/Kuroshio Current System (developed by our Japanese collaborators under a separate funded project). In this 2-year effort, short-term (one year) and long-term (decadal) simulations of sardine dynamics will be performed for the two systems to demonstrate the utility of physics to fish to fishers modeling and the power of the comparative approach for understanding how bottom-up (climate and physics) and top-down (predation and harvest) factors can affect small pelagic fish populations. Future efforts beyond this initial 2-year proposal will use the combined models in a more rigorous and systematic evaluation of alternative hypotheses about mechanisms underlying the low-frequency variability in sardine, anchovy, and other small pelagic species in a variety of systems. Results of this initial 2-year effort, and of subsequent efforts, will contribute to the mechanistic understanding and management of small pelagic fish stocks in the context of climate change.