Linking predator and prey through ocean dynamics in a submarine canyon

Submarine canyons are ecosystem hotspots in the deep sea. Here, we present data investigating how the environmental forcing in a submarine canyon mediates both predator and prey distribution. From March to July 2018, we deployed a mooring with a combination of passive and active acoustic instruments as well as a bottom-mounted Acoustic Doppler Current Profiler (ADCP) in the Southern California Bight at Tanner Basin (32° 39.5'N and 119° 28.6'W). This location is a known foraging hotspot for a pelagic top predator of management concern, Cuvier’s beaked whale (Ziphius cavirostris). We found a scattering layer located between 1040 and 1130 m deep, consistent with Z. cavirostris foraging depth in the region. Fluctuations in the backscatter intensity of this scattering layer occurred over multiple temporal scales. The most predominant fluctuations occurred at tidal frequencies, but large, low-frequency fluctuations over weekly time scales were also observed. These fluctuations in the prey field are linked to both the flows interacting with the topography of Tanner Basin and the overlying mesoscale flows. Our data demonstrate how dynamic the prey field of large marine predators is, even in the deep sea. The combination of tidal and mesoscale forcing drives a spatially and temporally patchy prey environment for predators foraging in the deep scattering layer.