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Marine Ecology Progress Series

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MEPS 479:283-302 (2013)  -  DOI:

Foraging behavior of northern fur seals closely matches the hierarchical patch scales of prey

Kelly J. Benoit-Bird1,*, Brian C. Battaile2, Chad A. Nordstrom2, Andrew W. Trites2

1College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, 104 CEOAS Administration Building, Corvallis, Oregon 97331, USA
2Marine Mammal Research Unit, University of British Columbia, Room 247, AERL, 2202 Main Mall, Vancouver, British Columbia V6T 1Z4, Canada

ABSTRACT: Marine prey often occur in hierarchical mosaics whereby small, high-density patches are nested inside of larger, lower density aggregations. We tested the extent to which the foraging behavior of a marine predator (northern fur seal Callorhinus ursinus) could be explained by the hierarchical patch structure of a dominant prey species (juvenile walleye pollock Theragra chalcogramma) in the eastern Bering Sea. Comparing the movements of satellite-tracked fur seals with ship-based acoustic surveys of prey revealed that fur seals did not randomly search for prey, but instead showed deviations in the distribution of step-lengths (distances between their foraging patches) corresponding to the distances between aggregations of prey. Scales of prey distribution varied between Bering Sea shelf and deep-water slope habitats, while spatial scale distributions of fur seals showed corresponding changes, indicating that their search strategies were not innate patterns decoupled from the environment. Fur seals tended to avoid the smallest prey patches in both shelf and slope habitats. They also avoided prey patches that were separated by large distances. Fur seals responded to several levels of prey patchiness simultaneously, resulting in strong correlations between predator and prey over the entire range of aggregation scales observed in juvenile pollock. Our results indicate that, despite having a varied diet, fur seal foraging paths were defined by juvenile pollock aggregations. The presence of hierarchical, scale-dependent aggregation in both predator and prey provides new insights into fur seal behavior and a means to predict the dynamics of their interactions with prey.

KEY WORDS: Patchiness · Spatial scale · Predator?prey · Foraging behavior · Hierarchical · Northern fur seal · Juvenile walleye pollock

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Cite this article as: Benoit-Bird KJ, Battaile BC, Nordstrom CA, Trites AW (2013) Foraging behavior of northern fur seals closely matches the hierarchical patch scales of prey. Mar Ecol Prog Ser 479:283-302.

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