Identification of Prey Captures in Australian Fur Seals (Arctocephalus pusillus doriferus) Using Head-Mounted Accelerometers: Field Validation with Animal-Borne Video Cameras

Abstract

This study investigated prey captures in free-ranging adult female Australian fur seals (Arctocephalus pusillus doriferus) using head-mounted 3-axis accelerometers and animal-borne video cameras. Acceleration data was used to identify individual attempted prey captures (APC), and video data were used to independently verify APC and prey types. Results demonstrated that head-mounted accelerometers could detect individual APC but were unable to distinguish among prey types (fish, cephalopod, stingray) or between successful captures and unsuccessful capture attempts. Mean detection rate (true positive rate) on individual animals in the testing subset ranged from 67-100%, and mean detection on the testing subset averaged across 4 animals ranged from 82-97%. Mean False positive (FP) rate ranged from 15-67% individually in the testing subset, and 26-59% averaged across 4 animals. Surge and sway had significantly greater detection rates, but also conversely greater FP rates compared to heave. Video data also indicated that some head movements recorded by the accelerometers were unrelated to APC and that a peak in acceleration variance did not always equate to an individual prey item. The results of the present study indicate that head-mounted accelerometers provide a complementary tool for investigating foraging behaviour in pinnipeds, but that detection and FP correction factors need to be applied for reliable field application.

Reproductive success is energetically linked to foraging efficiency in Antarctic fur seals

“…We are aware that PrCA represent attempts and not confirmed prey captures, but we assumed that unsuccessful PrCA were minor compared to successful ones (93% of attempts were successful in Australian fur seals [44], and that proportion of unsuccessful attempts were consistent between seals.…”

“…Detection rate of PrCA (true positive rate) is known to range from 68 to 97% (underestimation of true PrCA) and the false positive rate from 6 to 48% (overestimation of true PrCA) in Steller sea lions and Australian fur seals [28, 44]. Mean ± SD of FE i was calculated over the 1000 generated PrCA i , EE i and EC p using Eq 1.…”

Navigating uncertain waters: a critical review of inferring foraging behaviour from location and dive data in pinnipeds

“…Triaxial accelerometers can be particularly helpful to improve our understanding of 3D movement underwater. Head-mounted accelerometers have been used to identify prey-capture attempts in multiple species [12, 71, 77]. However, they can also be used to determine body position and horizontal displacement, and potentially elucidate the particular behaviours associated with individual dives [78].…”

“…Devices allow us to collect an increasing range of data that can be either archived and later retrieved, or autonomously transmitted via acoustic or satellite telemetry, or mobile phone technology (biotelemetry; see [3]). Such data include empirical observations of feeding attempts from fine-scale body movements such as jaw opening [9–11] and lunges measured using accelerometers [12–14], and even physiological measurements of feeding, such as changes in stomach temperature [15–17]. Animal-mounted cameras have complemented such information and contributed substantially to our understanding of how diving predators (both captive and in the wild) search for, capture and handle prey [9, 18–20].…”

Processing of acceleration and dive data on‐board satellite relay tags to investigate diving and foraging behaviour in free‐ranging marine predators

“…In particular, such information has revolutionised our ability to study the behaviours of diving predators, which often spend extended periods of time underwater and are thus hard to monitor. For example, prey catch attempt (PrCA) behaviours can be identified from peaks in acceleration indicative of rapid head movements (Gallon et al., ; Naito, Bornemann, Takahashi, McIntyre, & Plotz, ; Suzuki, Naito, Folkow, Miyazaki, & Blix, ; Viviant et al., ; Volpov, Hoskins, et al., ), whilst proxies of energetic expenditure (e.g. swimming effort) can be calculated by isolating dynamic movement rates (Jeanniard‐du‐Dot, Guinet, Arnould, Speakman, & Trites, ; Sato, Mitani, Cameron, Siniff, & Naito, ; Volpov, Rosen, Trites, & Arnould, ).…”