In situ measures of foraging success and prey encounter reveal marine habitat-dependent search strategies

• Published in: Ecology
• Main Authors: Thums, M., Bradshaw, C., Hindell, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Ecological Soc Amer 2011
• Subjects: area-restricted search; first-passage time; foraging success; Macquarie Island; Australia; Mirounga leonina; movement patterns; predictability; profitability; southern elephant seal; Antarctic; Antarc*; Elephant Seal; Elephant Seals; Southern Elephant Seal; Southern Elephant Seals
• Online Access: http://hdl.handle.net/2440/67040; https://doi.org/10.1890/09-1299.1

Predators are thought to reduce travel speed and increase turning rate in areas where resources are relatively more abundant, a behavior termed ‘‘area-restricted search.’’ However, evidence for this is rare, and few empirical data exist for large predators. Animals exhibiting foraging site fidelity could also be spatially aware of suitable feeding areas based on prior experience; changes in movement patterns might therefore arise from the anticipation of higher prey density. We tested the hypothesis that regions of area-restricted search were associated with a higher number of daily speed spikes (a proxy for potential prey encounter rate) and foraging success in southern elephant seals (Mirounga leonina), a species exhibiting both area-restricted searches and high interannual foraging site fidelity. We used onshore morphological measurements and diving data from archival tags deployed during winter foraging trips. Foraging success was inferred from in situ changes in relative lipid content derived from measured changes in buoyancy, and first-passage time analysis was used to identify area-restricted search behavior. Seals exhibited relatively direct southerly movement on average, with intensive search behavior predominantly located at the distal end of tracks. The probability of being in search mode was positively related to changes in relative lipid content; thus, intensively searched areas were associated with the highest foraging success. However, there was high foraging success during the outward transit even though seals moved through quickly without slowing down and increasing turning rate to exploit these areas. In addition, the probability of being in search mode was negatively related to the number of daily speed spikes. These results suggest that movement patterns represent a response to prior expectation of the location of predictable and profitable resources. Shelf habitat was 4–9 times more profitable than the other habitats, emphasizing the importance of the East Antarctic shelf for this and other ...