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

• Published in: Functional Ecology
• Main Authors: Viviant, Morgane, Jeanniard-Du-Dot, Tiphaine, Monestiez, Pascal, Authier, Matthieu, Guinet, Christophe
• Other Authors: Centre d'Études Biologiques de Chizé - UMR 7372 (CEBC), Institut National de la Recherche Agronomique (INRA)-La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS), Fisheries Centre (Marine Mammal Research Unit), University of British Columbia (UBC), Biostatistique et Processus Spatiaux (BioSP), Institut National de la Recherche Agronomique (INRA)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: foraging strategies; diving behaviour; aerobic diving limit; foraging depth; Antarctic fur seals; [SDE]Environmental Sciences; Antarctic; The Antarctic; Antarc*; Antarctic Fur Seal; Antarctic Fur Seals; Arctocephalus gazella
• Online Access: https://hal.science/hal-01324015; https://doi.org/10.1111/1365-2435.12675

Ministère de la Recherche, Université Pierre et Marie Curie International audience 1. 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.2. 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 analyzed (>15m 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.3. 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.4. For dives shallower than 55m, 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 1s). 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 55m, threshold beyond which the mean dive duration exceeded the apparent aerobic dive limit. For dives deeper than 55mAccepted Article This article is protected by copyright. All rights reserved.seals kept on foraging at bottom irrespective of the number of mouth-openings performed.5. Most dives occurred at shallower depths (30-55m) than the 60m depth of highest foraging efficiency (i.e. of greatest number of mouth-opening events per dive). This is likely related ...