Identification of prey captures in Australian Fur Seals (Arctocephalus pusillus doriferus) using head-mounted accelerometers: field validation with animal-borne video cameras

This study investigated prey captures in free-ranging adult female Australian fur seals (Arctocephalus pusillus doriferus) using head-mounted 3-axis accelerometers and animal-borne video cameras. Acceleration data was used to identify individual attempted prey captures (APC), and video data were used to independently verify APC and prey types. Results demonstrated that head-mounted accelerometers could detect individual APC but were unable to distinguish among prey types (fish, cephalopod, stingray) or between successful captures and unsuccessful capture attempts. Mean detection rate (true positive rate) on individual animals in the testing subset ranged from 67-100%, and mean detection on the testing subset averaged across 4 animals ranged from 82-97%. Mean False positive (FP) rate ranged from 15-67% individually in the testing subset, and 26-59% averaged across 4 animals. Surge and sway had significantly greater detection rates, but also conversely greater FP rates compared to heave. Video data also indicated that some head movements recorded by the accelerometers were unrelated to APC and that a peak in acceleration variance did not always equate to an individual prey item. The results of the present study indicate that head-mounted accelerometers provide a complementary tool for investigating foraging behaviour in pinnipeds, but that detection and FP correction factors need to be applied for reliable field application

Optimisation du comportement d'acquisition des ressources au cours de la plongée (cas de l'otarie à fourrure antartique)

Prédire la réponse des prédateurs marins aux changements climatiques nécessite de comprendre leur écologie alimentaire. L objectif de la thèse était d étudier les stratégies de chasse de l otarie à fourrure Antarctique dans le cadre des théories de l approvisionnement optimal. Comment les otaries ajustent-elles leur comportement de plongée selon la qualité de l environnement (abondance et accessibilité des proies en profondeur) et leurs contraintes physiologiques (limite de plongée aérobie, ADL) ? Une méthodologie basée sur les accéléromètres fut développée afin de détecter les tentatives de capture (i.e. rencontres) de proies de ces animaux. Notre étude montre que les otaries concentrent leurs plongées à des profondeurs inférieures aux profondeurs de densité maximale de proies. Au-delà de 55-60 mètres, elles sont physiologiquement contraintes (dépassent leur ADL en moyenne) et font face à un compromis entre la disponibilité et l accessibilité des proies. Cette contrainte affecte leurs stratégies de chasse : des plongées d exploration ne sont utilisées qu à faible profondeur. Contrairement aux prédictions, elles augmentent leur effort de recherche alimentaire dans les parcelles de proies de mauvaise qualité, à l échelle des nuits. La prise en compte des contraintes physiologiques et des échelles temporelles est donc cruciale pour prédire le succès de pêche des prédateurs marins. Avec le réchauffement climatique, les scientifiques prédisent un approfondissement de la thermocline, et donc des proies. Les otaries à fourrure étant rapidement contraintes avec la profondeur, cela est susceptible d affecter négativement leur succès alimentaire et in fine leur succès reproducteurPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Estimation indirecte d'un champ de ressources à partir d'un ensemble de trajectoires d'animaux qui l'exploitent

National audienc

Can We Predict Foraging Success in a Marine Predator from Dive Patterns Only? Validation with Prey Capture Attempt Data

<div><p>Predicting how climatic variations will affect marine predator populations relies on our ability to assess foraging success, but evaluating foraging success in a marine predator at sea is particularly difficult. Dive metrics are commonly available for marine mammals, diving birds and some species of fish. Bottom duration or dive duration are usually used as proxies for foraging success. However, few studies have tried to validate these assumptions and identify the set of behavioral variables that best predict foraging success at a given time scale. The objective of this study was to assess if foraging success in Antarctic fur seals could be accurately predicted from dive parameters only, at different temporal scales. For this study, 11 individuals were equipped with either Hall sensors or accelerometers to record dive profiles and detect mouth-opening events, which were considered prey capture attempts. The number of prey capture attempts was best predicted by descent and ascent rates at the dive scale; bottom duration and descent rates at 30-min, 1-h, and 2-h scales; and ascent rates and maximum dive depths at the all-night scale. Model performances increased with temporal scales, but rank and sign of the factors varied according to the time scale considered, suggesting that behavioral adjustment in response to prey distribution could occur at certain scales only. The models predicted the foraging intensity of new individuals with good accuracy despite high inter-individual differences. Dive metrics that predict foraging success depend on the species and the scale considered, as verified by the literature and this study. The methodology used in our study is easy to implement, enables an assessment of model performance, and could be applied to any other marine predator.</p></div

Observations versus predicted values of prey capture attempts for “leave-one-out” cross-validations.

<p>These relationships are presented for the dive (A), dive bout (B), night (C), 30 min (D), 1 h (E) and 2 h (F) scales. Generalized linear mixed models were used for all time scales except the night scale, where a generalized linear model was used. Each color represents a different individual (ID).</p

Dive profiles.

<p>Descent, bottom, and ascent phases are in dark green, cream, and light green, respectively. Steps in the descent phase and descending steps in the bottom phase are in light purple. Steps in the ascent and ascending steps in the bottom phase are in dark purple. Wiggles are in blue.</p

Dive profile with several steps descending in the bottom phase (light purple).

<p>These successive steps generally lead to a high variation of depth in the bottom phase. Prey capture attempts are symbolized by pink dots.</p

Results of model averaging based on the best predictive models for number of prey capture attempts at different temporal scales.

<p>Coefficient of predictive models developed at each time scale (mean ± standard error). All models used for model averaging are generalized linear mixed models except at the night scale where generalized linear models were used. The concordance index (C-index) is shown for final averaged models on complete data sets and for cross-validations. NI: nonincluded predictor; NS: nonselected predictors. Explanatory variables correspond to raw values for the dive scale and to mean values for greater scales, except the number of dives and percent of time (cumulated dive cycle duration) for dives greater than 15 m.</p

Observations versus fitted values of prey capture attempts on the entire data set.

<p>This relationship is shown at the dive (A), dive bout (B), night (C), 30 min (D), 1 h (E) and 2 h (F) scales. Final averaged generalized linear mixed models were used to estimate fitted values at every time scale with the exception of the night scale, where a generalized linear model was used.</p

Foraging in the darkness of the Southern Ocean: influence of bioluminescence on a deep diving predator.

How non-echolocating deep diving marine predators locate their prey while foraging remains mostly unknown. Female southern elephant seals (SES) (Mirounga leonina) have vision adapted to low intensity light with a peak sensitivity at 485 nm. This matches the wavelength of bioluminescence produced by a large range of marine organisms including myctophid fish, SES's main prey. In this study, we investigated whether bioluminescence provides an accurate estimate of prey occurrence for SES. To do so, four SES were satellite-tracked during their post-breeding foraging trip and were equipped with Time-Depth-Recorders that also recorded light levels every two seconds. A total of 3386 dives were processed through a light-treatment model that detected light events higher than ambient level, i.e. bioluminescence events. The number of bioluminescence events was related to an index of foraging intensity for SES dives deep enough to avoid the influence of natural ambient light. The occurrence of bioluminescence was found to be negatively related to depth both at night and day. Foraging intensity was also positively related to bioluminescence both during day and night. This result suggests that bioluminescence likely provides SES with valuable indications of prey occurrence and might be a key element in predator-prey interactions in deep-dark marine environments