Estimating resource acquisition and at-sea body condition of a marine predator

1. Body condition plays a fundamental role in many ecological and evolutionary processes at a variety of scales and across a broad range of animal taxa. An understanding of how body condition changes at fine spatial and temporal scales as a result of interaction with the envi-ronment provides necessary information about how animals acquire resources. 2. However, comparatively little is known about intra- and interindividual variation of condi-tion in marine systems. Where condition has been studied, changes typically are recorded at relatively coarse time-scales. By quantifying how fine-scale interaction with the environment influences condition, we can broaden our understanding of how animals acquire resources and allocate them to body stores. 3. Here we used a hierarchical Bayesian state-space model to estimate the body condition as measured by the size of an animal’s lipid store in two closely related species of marine preda-tor that occupy different hemispheres: northern elephant seals (Mirounga angustirostris) and southern elephant seals (Mirounga leonina). The observation model linked drift dives to lipi