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

• Published in: Ecology
• Main Authors: Thums, M, Bradshaw, CJA, Hindell, MA
• Format: Article in Journal/Newspaper
• Language: English
• Published: Ecological Soc Amer 2011
• Subjects: Biological Sciences; Ecology; Marine and Estuarine Ecology (incl. Marine Ichthyology); Antarc*; Elephant Seals; Mirounga leonina; Southern Elephant Seals
• Online Access: https://doi.org/10.1890/09-1299.1; http://www.ncbi.nlm.nih.gov/pubmed/21797154; http://ecite.utas.edu.au/76846

Predators are thought to reduce travel speed and increase turning rate in areaswhere 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. Animalsexhibiting foraging site fidelity could also be spatially aware of suitable feeding areas based onprior experience; changes in movement patterns might therefore arise from the anticipation ofhigher prey density. We tested the hypothesis that regions of area-restricted search wereassociated with a higher number of daily speed spikes (a proxy for potential prey encounterrate) and foraging success in southern elephant seals ( Mirounga leonina ), a species exhibitingboth area-restricted searches and high interannual foraging site fidelity. We used onshoremorphological measurements and diving data from archival tags deployed during winterforaging trips. Foraging success was inferred from in situ changes in relative lipid contentderived from measured changes in buoyancy, and first-passage time analysis was used toidentify area-restricted search behavior. Seals exhibited relatively direct southerly movementon 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 lipidcontent; thus, intensively searched areas were associated with the highest foraging success.However, there was high foraging success during the outward transit even though seals movedthrough quickly without slowing down and increasing turning rate to exploit these areas. Inaddition, the probability of being in search mode was negatively related to the number of dailyspeed spikes. These results suggest that movement patterns represent a response to priorexpectation of the location of predictable and profitable resources. Shelf habitat was 49 timesmore profitable than the other habitats, emphasizing the importance of the East Antarcticshelf for this and other predators in the region. We have provided rare empirical data withwhich to investigate the relationship between predator foraging strategy and prey encounter/foraging success, underlining the importance of inferring the timing and spatial arrangementof successful food acquisition for interpreting foraging strategies correctly.