UC San Diego

In marine ecosystems, cetaceans are top predators that mostly exploit low- to mid-trophic level organisms. The presence and type of behavior displayed by cetaceans within a habitat is thus strongly driven by the physical oceanographic conditions that modulate the local prey. However, our understanding of how physical oceanography shapes foraging resources for cetaceans is still lacking due to the difficulty of simultaneously and continuously collecting prey and cetacean presence data. This study used passive acoustic, active acoustic, and in situ physical oceanographic observations collected from moorings located within the San Diego Trough, along with satellite-derived and ocean general circulation model measurements, to characterize the local ecosystem and generate generalized additive models to examine how physics influences the relationships between lower and higher trophic levels. Here, I show how seasonal changes in oceanography and mesoscale variability modulate prey availability and thus cetacean presence and behavior within the San Diego Trough. Specifically, I found that surface prey was modulated by changes in mesoscale activity, diel vertically migrating mesopelagic species were modulated by wind-driven upwelling and primary productivity, and krill in the mid-water column were modulated by wind-driven upwelling, salinity at ~300 m depth, and primary productivity. These relationships were then reflected in the cetacean models, where the presence and type of behavior displayed by a group of cetaceans was influenced either by both the presence of their prey and the physical oceanographic conditions that modulate their prey, or by just the physical oceanographic conditions that modulate their prey. These results describe the predator-prey dynamics of some of the cetaceans found within the San Diego Trough and may aid in developing more accurate spatially explicit management actions to better manage and conserve these species in similar ecosystems.