Temporal scales of foraging in a marine predator: implications for interpreting the distribution of prey

The pattern of prey distribution can profoundly affect the foraging behavior and success of a predator. In pelagic marine ecosystems, where prey is often patchily distributed, predators must be able to adapt quickly to changes in the spatial patterning of prey. Antarctic fur seals feed primarily on krill, which is patchily distributed. When combined with information about swimming speed on the surface, the time taken for a fur seal to locate a new patch after leaving an old one is an indication of the distance between patches. The frequency distribution of intervals between bouts of foraging showed that fur seals foraged at two spatial distributions: (1) a fine-scale (median distance 0.18 - 0.27 km) represented by short (<5 min) travel durations between patches; and (2) a courser or meso-scale (median distance 1.3 - 1.6 km) represented by longer (>5 rain) travel durations. In a study lasting 5 years, the distributions of travel durations between bouts of feeding changed between years. These changes suggested either that the structure and/or the spatial distribution of krill swarms varied between years. The behavior of fur seals suggested that there was overall clumping of prey at the fine-scale but there was a more even spacing of prey patches at the meso-scale level. Only in one year of the study (1990/91) were there indications that fur seals had difficulty in finding enough food. Fur seal behavior suggested that there was no reduction in the number of prey patches available in that year but that prey patches were of poorer quality. The study showed how predator behavior can provide valuable information about the functional relationship between prey dispersion and predator performance.