An air-breathing marine mammal optimises foraging by decreasing dive effort with increasing resource quality

Understanding how air-breathing diving animals respond to resource quality is foundational to studying their foraging ecology. We quantified relationships between southern elephant seal dive effort and resource quality – informed by estimates of at-sea body condition – across sexes, habitats, and temporal scales. After accounting for buoyancy effects, we found seals responded consistently to changes in resource quality. Irrespective of sex and foraging habitat, seals increased transit (ascent, descent) rates and decreased depth-offset dive durations when resource quality was high. Our work reconciles conflicting predictions of both increasing and decreasing dive effort with increasing resource quality. This emphasises the importance of scale, showing that while seals may spend relatively more time in high quality food patches for a given resource quality, they spend less time on average per patch when resource quality is high. This is important for inferences of foraging habitat quality drawn from dive behaviour alone.This repository holds the supporting datasets and code used to generate the results of this study. Please refer to the README.docx for a description of each file, and the definition of variables within the test dataset.