Should I stay or should I go? Behavioral adjustments of fur seals related to foraging success

Abstract

Understanding foraging strategies and decision-making processes of predators provide crucial insights into how they might respond to changes in prey availability and in their environment to maximize their net energy input. In this work, foraging strategies of Antarctic fur seals (Arctocephalus gazella, AFS) and Northern fur seals (Callorhinus ursinus, NFS) were studied to determine how they adjust their foraging behavior according to their past prey capture experiences. AFS on Kerguelen Islands are exclusively oceanic divers, while NFS population of St Paul Island shows both oceanic and neritic divers. We thus hypothesized that the two species would respond differently to a change in prey capture success depending on their foraging strategy. To test this, 40 females were equipped with tags that measured tri-axial acceleration, dive depth, and GPS coordinates, from which we derived prey capture attempts and behavioral metrics. Influence of prey capture success on horizontal and vertical movements of seals was investigated at different time scales: multi-dive, night, and trip. Both AFS and NFS traveled further during the day if they encountered low prey capture periods during the previous night. However, at the multi-dive scale, neritic NFS differed from oceanic NFS and AFS in terms of decision-making processes, e.g., both AFS and oceanic NFS dived deeper in response to low prey capture rate periods, while neritic NFS did not. Similarities in decision-making processes between NFS and AFS foraging on pelagic prey suggest that pelagic vs. neritic prey type is a key factor in defining foraging decisions of diving marine predators.

Underwater vocalizations in foraging female Antarctic fur seals (Arctocephalus gazella) in the Kerguelen Islands

“…While we cannot test this hypothesis, we were able to study the fine‐scale hunting behavior of AFS to infer information on prey behavior. In particular, a previous study using sonar and movement tags showed that evasive prey were associated with higher swimming efforts and longer prey capture events (Chevallay et al, 2023). Here we compared these two behavioral parameters between the female that consistently produced calls (ind.…”

“…Prey capture attempts (PrCAs hereafter) were detected from the 250 Hz tri‐axial acceleration data recorded by tags, by computing the norm of the differential of the tri‐axial acceleration (norm‐jerk hereafter), as described in (Chevallay et al, 2023). Spikes in the norm‐jerk signal higher than 3,000 m/s 2 were classified as prey strikes (Chevallay et al, 2023).…”

“…Prey capture attempts (PrCAs hereafter) were detected from the 250 Hz tri‐axial acceleration data recorded by tags, by computing the norm of the differential of the tri‐axial acceleration (norm‐jerk hereafter), as described in (Chevallay et al, 2023). Spikes in the norm‐jerk signal higher than 3,000 m/s 2 were classified as prey strikes (Chevallay et al, 2023). As prey may be encountered in patches or may elude capture, leading to a bout structure in prey strikes, strikes occurring less than 15 s from the previous strike were grouped in the same PrCA bout according to the distribution of interstrike intervals (Chevallay et al, 2023).…”

“…Spikes in the norm‐jerk signal higher than 3,000 m/s 2 were classified as prey strikes (Chevallay et al, 2023). As prey may be encountered in patches or may elude capture, leading to a bout structure in prey strikes, strikes occurring less than 15 s from the previous strike were grouped in the same PrCA bout according to the distribution of interstrike intervals (Chevallay et al, 2023). Dives where at least one strike was detected were classified as hunting dives.…”

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

“…These plots showed a bimodal distribution with a minimum at 3000 m.s -2 for all individuals, and was set as a threshold to identify strikes in the full norm-jerk series. As prey may be encountered in patches or may elude capture, leading to a bout structure in prey strikes, strikes occurring less than 15 s from the previous strike were grouped in the same PrCA bout (referred as bout hereafter) according to the distribution of inter-strike interval (Chevallay et al, in revision).…”