The hunter or the hunted? Inferring benthic meso-predator behavior from swim velocity data.

Abstract

Background: Air-breathing benthic predators must balance foraging with exposure risk under strict oxygen constraints. Animal-borne video data from Australian fur seals (Arctocephalus pusillus doriferus; AUFS) has documented prolonged immobility on the sea-floor, but the prevalence, organization, and functional significance of this behavior remain unclear.

Methods: Swim velocity and dive-behavior data from adult female AUFS were analyzed to identify Sea-floor Stationary Dives (SFSD), defined as dives in which ≥50% of the bottom phase occurred at zero swim speed. Temporal variation was assessed using Generalized Additive Models with individual identity as a random effect. Sequential organization was evaluated using run-length distributions and permutation tests (10,000 randomizations preserving each individual's dive-type totals). Spatial recurrence was examined qualitatively using locations from two GPS-instrumented females. Dive-cycle characteristics associated with SFSD were compared with other benthic dive types.

Results: SFSD comprised ∼2% of all benthic dives and showed pronounced crepuscular peaks with substantial individual heterogeneity. Sequential analyses revealed multi-dive SFSD bouts in a subset of individuals, with significant clustering relative to random expectations. SFSD were associated with intermediate bottom times and short surface intervals, indicating compressed dive cycles. Qualitative spatial patterns from two Global Positioning System (GPS)-instrumented females suggested recurrence of SFSD within localized areas across multiple foraging trips.

Conclusions: The timing, clustering, and dive-cycle characteristics of SFSD suggest this behavior is not associated primarily with ambush predation or resting. Instead, they are most consistent with a predator-avoidance response by air-breathing divers vulnerable in an open sea-scape. These findings highlight the importance of predation risk in shaping dive organization and habitat use in benthic marine predators.