DOI: 10.5061/dryad.ct511
title: Data from: Bottom time does not always predict prey encounter rate in Antarctic fur seals

description: 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 (&gt;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-opening
 events. However, this difference was only due to the occurrence of
 V-shaped dives with short bottom durations (0 or 1 s). When removing those
 V-shaped dives, bottom duration was not related to the presence of
 mouth-openings anymore. Thus, the decision to abandon foraging is likely
 related to other information about prey availability than prey capture
 attempts (i.e. sensory cues) that seals collect during the descent phase.
 We did not observe V-shaped dives for dives deeper than 55 m, threshold
 beyond which the mean dive duration exceeded the apparent aerobic dive
 limit. For dives deeper than 55 m, seals kept on foraging at bottom
 irrespective of the number of mouth-openings performed. Most dives
 occurred at shallower depths (30–55 m) than the 60 m depth of highest
 foraging efficiency (i.e. of greatest number of mouth-opening events per
 dive). This is likely related to physiological constraints during deeper
 dives. We suggest that foraging decisions are more complex than predicted
 by current theory and highlight the importance of the information
 collected by the predator during the descent as well as its physiological
 constraints. Ultimately, this will help establishing reliable predictive
 foraging models for marine predators based on diving patterns only.
description: Fur_seal_dive_capture_dataThis file is an excel data files regrouping the complete dive data set used in this paper. each column are clearly labbelled Campain: field season; fur seal pup ID use to identify the female; female size in cm; female mass in kg; night index, form 0 (first night spent at sea, to a maximal value corresponding to the last night recorded); Dive_ID: an incremental dive number for a given female form the first dive to the last dive available for that female. Start_time_dt : date and time at the beginning of the dive,Max_Depth:_m : maximun diving depth for the corresponding dive, surf_before: time spent at surface prior to the dive; desc_time_s : duration in second of the descent phase of the dive, Bottom_time_s: duration in seconds of the bottom phase of the dive; asc_time_s: duraction in seconds of the ascent phase of the dive; depth_end_desc_m: depth in meter at the end of the decent phase of the dive; depth_start_asc_m: depth in meters at the begining of the ascent phase of the dive; desc_speed_ms-1: descent speed during the descent phase of the dive in meter per seconds; Asc_speed_ms-1: ascent speed during the ascent phase of the dive in meter per seconds; Prey_Capture _Attempts : total number of prey capture attempts during the complete dive; capture_mean_depth_m : mean depth of the capture attempts for the dive; nb_captures_desc : number of prey capture attempts during the descent phase of the dive; nb_captures_bottom : number of prey capture attempts during the bottom phase of the dive; nb_captures_asc: number of prey capture attempts during the ascent phase of the dive