Sealing the deal - Antarctic fur seals' active hunting tactics to capture small evasive prey revealed by miniature sonar tags

Abstract

Fine-scale interactions between predators and their prey are key factors determining both predators hunting efficiency and prey survival. The ability to adopt hunting tactics that minimise the risk of triggering an escape reaction from the prey is crucial for an efficient foraging, and is contingent to detection capabilities and locomotor performances of both predators and prey. In this study, we aimed at describing fine-scale predator-prey interactions in female Antarctic fur seals (Arctocephalus gazella, AFS hereafter), a small pinniped foraging on evasive prey. Our objectives were (1) to describe characteristics of prey targeted by female AFS to assess prey selection in this species; (2) to estimate the timing of prey detection by AFS and prey reaction to the AFS approach, and (3) to describe AFS hunting tactics, i.e. fine-scale AFS posture and swimming activity during prey capture events. In fine, we seek to better understand AFSs efficiency at exploiting their small prey. To do so, we used data recorded by a newly developed sonar tag that combines active acoustics with ultra-high resolution movement sensors to study simultaneously the fine-scale behaviour of both AFS and prey during predator-prey interactions. We analysed more than 1200 prey capture events in eight female AFS and showed that AFS and their prey detect each other at the same time, i.e. 1-2 seconds before the strike, forcing AFS to display reactive fast-moving chases to capture their prey. Prey detection was consistently followed by bursts of accelerations from AFS, which lasted longer for evasive prey. We suggest that the ability of AFS to perform bursts of accelerations may allow them to target evasive prey. This active hunting tactics is likely very energy-consuming but might be compensated by the consumption of highly nutritious prey.