Southern elephant seals replenish their lipid reserves at different rates according to foraging habitat

Assessing energy gain and expenditure in free ranging marine predators is difficult. However,
such measurements are critical if we are to understand how variation in foraging efficiency,
and in turn individual body condition, is impacted by environmentally driven changes
in prey abundance and/or accessibility. To investigate the influence of oceanographic habitat
type on foraging efficiency, ten post-breeding female southern elephant seals Mirounga
leonina (SES) were equipped and tracked with bio-loggers to give continuous information of
prey catch attempts, body density and body activity. Variations in these indices of foraging
efficiency were then compared between three different oceanographic habitats, delineated
by the main frontal structures of the Southern Ocean. Results show that changes in body
density are related not only to the number of previous prey catch attempts and to the body
activity (at a 6 day lag), but also foraging habitat type. For example, despite a lower daily
prey catch attempt rate, SESs foraging north of the sub-Antarctic front improve their body
density at a higher rate than individuals foraging south of the sub-Antarctic and polar fronts,
suggesting that they may forage on easier to catch and/or more energetically rich prey in
this area. Our study highlights a need to understand the influence of habitat type on top
predator foraging behaviour and efficiency when attempting a better comprehension of
marine ecosystems.