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

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

Distribution of surface oxygen in the physical context of the Southern Ocean.

<p>a) In 2010, the more oxygenated waters were mainly located south to the Fawn Through Current (FTC), also called the surface expression of the Polar Front and here symbolized by the 0.5°C isotherm. b) In 2011, the surface waters North to the Subantarctic Front (SAF) were low oxygenated compared to surface waters located South to the Polar Front. Within the Polar Frontal Zone (PFZ), no clear pattern appears in the distribution of dissolved oxygen regarding to the main physical structures.</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

Zoomed location of seal and Keops profiles that have been compared.

<p>The selected profiles are in red (large dots = Keops; small dots = Seals). The letters a,b & c correspond to the profiles presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132681#pone.0132681.g003" target="_blank">Fig 3</a>.</p

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

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

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

Location of oxygen profiles recorded by Kerguelen elephant seals and the ship survey Keops2.

<p>The seal profiles were obtained during the post-breeding foraging trip of 5 females. The individual #1 was equipped in October 2010. The 4 other females (#2 to #5) were equipped in October 2011. Blue dots correspond to the Keops2 stations (Keops St). The Keops survey was conducted in October and November 2011. Isobaths are illustrated in light gray.</p

Temperature-Salinity diagram from seal data.

<p>Points are coloured by oxygen values. SAZ = Sub-Antarctic Zone, PFZ = Polar Frontal Zone, AZ = Antarctic Zone.</p