Bottom time does not always predict prey encounter rate in Antarctic fur seals

Optimal foraging models applied to breath-holding divers predict that diving predators should optimize the time spent foraging at the bottom of dives depending on prey encounter rate, distance to prey patch (depth) and physiological constraints.
We tested this hypothesis on a free-ranging diving marine predator, the Antarctic fur seal Arctocephalus gazella, equipped with accelerometers or Hall sensors (n = 11) that recorded mouth-opening events, a proxy for prey capture attempts and thus feeding events. Over the 5896 dives analysed (>15 m depth), the mean number of mouth-opening events per dive was 1·21 ± 1·69 (mean ± SD). Overall, 82% of mouth-openings occurred at the bottom of dives.
As predicted, fur seals increased their inferred foraging time at the bottom of dives with increasing patch distance (depth), irrespective of the number of mouth-openings.
For dives shallower than 55 m, the mean bottom duration of dives without mouth-openings was shorter than for dives with mouth-op...