MEPS 573:255-268 (2017)  -  DOI: https://doi.org/10.3354/meps12191

ABSTRACT: Few studies have examined the foraging ecology of top marine predators by taking into account the vertical and horizontal dimensions simultaneously. In this study, using 3-dimensional reconstruction of underwater animal paths, we investigated the relationship between area restricted search (ARS) and foraging behaviors in the southern elephant seal Mirounga leonina. We equipped 6 post-breeding females on the Kerguelen Islands with an Acousonde™ recording simultaneously sounds, pressure, acceleration and magnetic field-strength in 3-dimensions (n = 879 dives). Using the spherical first passage time analysis, we identified ARS in 46.4% of the dives. They represented 36.9% of the bottom time, but due to a higher prey encounter rate, 67.6% of catch attempts took place in ARS. These areas, occurring within a sphere of 48.2 ± 25.7 m radius, were characterized by an increase in energy expenditure and a strong variability in the roll and heading compared to non-ARS regions. While within an ARS, we identified 3 hunting modes from unsupervised classification based on acceleration properties previous to captures. We found that 32.8% of attempts matched a passive-gliding approach from above the target. The other 2 modes corresponded to an actively swimming approach associated with increases of variance in heading and/or rolling movements for the first one (56.6% of captures), and to a much larger swimming effort for the second one (10.6% of captures). These data revealed a strong link between seals’ fine-scale movements and feeding activity, suggesting that seals fed mainly on patchily distributed resources, with different hunting strategies that may be indicative of several prey species targeted.

KEY WORDS: Area restricted search · Foraging · Accelerometer · Acousonde™ · Data mining · Unsupervised classification · Machine learning · Spherical first passage time