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Marine Ecology Progress Series

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MEPS 404:275-287 (2010)  -  DOI:

Influence of prey behaviour and other predators on the foraging activities of a marine avian predator in a Low Arctic ecosystem

Gail K. Davoren1,*, Stefan Garthe2, William A. Montevecchi3, Silvano Benvenuti4

1Department of Biological Sciences, Duff Roblin Building, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
2Research and Technology Centre (FTZ), University of Kiel, Hafentörn 1, 25761 Büsum, Germany
3Departments of Psychology and Biology, Ocean Science Centre, Memorial University of Newfoundland, St. Johns, Newfoundland A1B 3X9, Canada
4Dipartimento di Etologia, Ecologia ed Evoluzione, University of Pisa, Via A. Volta 6, 56126 Pisa, Italy

ABSTRACT: Air-breathing marine predators can expend considerable time and energy searching for patchily distributed prey and, thus, likely employ varying foraging strategies to minimize these costs. We studied the diurnal foraging patterns of the northern gannet Sula bassana along with the distributional patterns of its main prey, capelin Mallotus villosus, off the NE Newfoundland coast from 1999 to 2005. We explored whether gannets minimize searching costs for near-surface (<30 m) capelin by (1) aggregating in shallow waters (<30 m) where capelin are accessible throughout the day, (2) aggregating in deeper waters where they concentrate foraging effort at dawn and dusk, when diel vertical migrations make capelin accessible, or (3) associating with other marine predators that increase the accessibility of capelin. We integrated continuous recordings of gannet foraging activities with vessel-based survey data on the density and distributional patterns of capelin, gannets and whales. Capelin typically comprised >70% of gannet diets. Gannets aggregated in shallow areas (<30 m) where spatially and temporally persistent shoals of capelin were accessible through daylight, but were also found in deeper water where capelin were inaccessible. Gannet diving activity was only recorded during daylight, and although activity peaked at the start and end of daylight, most dives occurred when capelin had migrated to inaccessible depths. Gannets were more tightly associated with whales than with near-surface capelin shoals, suggesting that they may successfully track capelin by cueing to the foraging activities of whales. A mixed strategy of memory-based and local enhancement foraging tactics appear to play important roles in minimizing the effort required to access prey.

KEY WORDS: Diet · Diel vertical migration · Whale-seabird associations · Memory-based foraging · Local enhancement · Capelin

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Cite this article as: Davoren GK, Garthe S, Montevecchi WA, Benvenuti S (2010) Influence of prey behaviour and other predators on the foraging activities of a marine avian predator in a Low Arctic ecosystem. Mar Ecol Prog Ser 404:275-287.

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