Fine-scale Oceanographic Drivers of Foraging in California Blue Whales

Animals integrate information from their environment to find food, but the environmental cues that drive this process are difficult to study and remain less understood. At broad spatial scales (e.g. the California Current), blue whale (Balaenoptera musculus) movement may be driven by memory, yet blue whales are known to target highly dynamic prey patches at fine spatial scales. To better understand how movement and sensory processes connect across different temporal and spatial scales, we analyzed surface location, diving, temperature and feeding data from 9 high-resolution multi-sensor tags (mean duration 14.34 days) from 2016-2018 to quantify blue whale foraging in relation to fine-scale oceanographic features measured by concurrently sampled high frequency radar (2-6 km, hourly resolution) along the California Coast. We show that blue whale feeding bouts were associated with anticyclonic oceanographic features (i.e. negative sea surface vorticity) at the scale of sub-daily movements. Tag-derived dive-temperature profiles revealed that the water columns associated with negative sea surface vorticity exhibited a substantially deeper thermocline than areas of positive vorticity, implying that localized downwelling may be an important foraging cue for blue whales. This approach will now be applied to a larger dataset that includes 64 individual tag deployments from 2014-2018 to validate these findings and test other variables. These results give insight into the drivers of animal movement at sub-daily scales and may have important implications for spatial ecology and conservation of endangered marine species.