Searching for prey in a three‐dimensional environment: hierarchical movements enhance foraging success in northern elephant seals

• Published in: Functional Ecology
• Main Authors: Adachi, Taiki, Costa, Daniel P., Robinson, Patrick W., Peterson, Sarah H., Yamamichi, Masato, Naito, Yasuhiko, Takahashi, Akinori
• Other Authors: Goldbogen, Jeremy, Japan Society for the Promotion of Science
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2016
• Subjects: Elephant Seal; Elephant Seals
• Online Access: http://dx.doi.org/10.1111/1365-2435.12686; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2F1365-2435.12686; https://onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2435.12686; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/1365-2435.12686; https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2435.12686

Summary Foraging theory predicts that predators adjust their movements according to the spatial distribution of prey. Since prey is often patchily distributed, area‐restricted search ( ARS ) behaviour, characterized by sinuous search paths of predators with increased turning frequency, should be effective in foraging. However, it remains unclear whether ARS behaviour actually enhances foraging success in free‐ranging animals, especially in marine animals that forage in a three‐dimensional (3D) environment. Here, we reconstructed 3D dive paths of a highly pelagic marine predator, the northern elephant seal ( n = 3), with multisensor data loggers that recorded depth, tri‐axis acceleration, tri‐axis magnetism and swim speed. We identified spatial scales of volume‐restricted search ( VRS , termed for 3D ARS ) behaviour using spherical first‐passage time analysis on 3D dive paths, accompanied with quantifying feeding rates in VRS by using mandible accelerometers that recorded feeding events. Seals exhibited VRS behaviour at two spatial scales (radius of spheres): small‐ VRS (8–10 m) and large‐ VRS (17–19 m). Most feeding events occurred in VRS zones (78 and 86% for small and large‐ VRS , respectively), although VRS accounted for a small proportion of bottom phase of dives in distance travelled. This suggests a strong link between VRS behaviour and foraging success. There was a hierarchical structure to the VRS most small‐ VRS (95%) were nested within large‐ VRS (i.e. nested VRS ). Importantly, nested VRS had significantly higher feeding rates than non‐nested VRS , because nested VRS contained small‐ and large‐ VRS with higher and lower feeding rates, respectively. These results suggest that seals forage on mesopelagic prey in a hierarchical patch system where high‐density patches at small scales are nested within low‐density patches at larger scales. We demonstrated that seals employed scale‐dependent, hierarchical 3D movements and that underwater fine‐scale sinuous movements (i.e. VRS ) were strongly linked to ...