Identifying physical drivers of predator-prey hotspots in the California Current Ecosystem

Understanding the influence of physical ocean conditions including temperature, currents, and primary productivity on predator-prey relationships in the California Current Ecosystem (CCE) is a significant component of ecosystem-based management. Euphausiids (krill) are key prey items for a wide range of seabirds, marine mammals, and commercially important fish, including Pacific hake (Merluccius productus). Variation in krill distribution and abundance can influence hake growth, abundance, and recruitment to the fishery. Thus, identifying the presence and persistence of krill hotspots, and their physical drivers, will inform predictions of hake abundance and distribution under variable prey conditions. We present a CCE-wide analysis of krill and hake distribution using a recently developed coast-wide time-series (2003-2017, n=9 surveys) of krill biomass from the biennial joint US-Canada acoustic-trawl survey for Pacific hake. The simultaneous collection of krill and hake data allows us to directly evaluate relationships between an important prey item in the CCE and an abundant predator. We used kernel density estimation to first visualize and identify krill and hake hotspots separately, and then evaluated the spatial correlations of the hotspots. We also assessed the influence of physical conditions including bathymetry, temperature, and chlorophyll-a on the presence, persistence, and correlations of krill-hake hotspots. Both krill and hake hotspots were located along the 200-m isobath in water depths of 100-300 meters between Monterey Bay, CA and Haida Gwaii, BC, indicating that krill are available to hake and other predators throughout the CCE. However, spatial correlations between krill and hake hotspots were stronger in the southern part of the CCE compared to the northern CCE, and varied annually. This suggests that the physical drivers influencing predator-prey hotspots are different, and vary along the coast. The results of this study will inform research on the formation and persistence of prey hotspots for shifting predator distributions under climate change.