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Marine Ecology Progress Series

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MEPS 431:267-279 (2011)  -  DOI:

Development of foraging strategies with age in a long-lived marine predator

Greg A. Breed1,3,*, W. Don Bowen2, Marty L. Leonard1

1Department of Biology, Dalhousie University, 1355 Oxford Street, Halifax, Nova Scotia B3H 4J1, Canada
2Bedford Institute of Oceanography, 1 Challenger Drive, Dartmouth, Nova Scotia, B2Y 4A2, Canada
3Present address: Harvard Forest, Harvard University, 324 North Main Street, Petersham, Massachusetts 01366, USA

ABSTRACT: The development of foraging strategies as animals mature depends upon experience, stage-specific physiology, the onset of reproductive maturity and the reproductive costs incurred by each sex. To understand the ontogeny of foraging behaviour, we compared movement behaviour of 24 young-of-year (YOY) juveniles (12 male, 12 female) with 6 subadult (4 male, 2 female) and 81 adult (43 male, 38 female) grey seals Halichoerus grypus. We used a behaviour discriminating state-space model followed by a series of mixed-effects models to examine trip structure and habitat use in these age classes. In foraging trips, tortuosity and speed of outbound travel were not different in YOY, subadults and adults, suggesting that YOY navigate as well as older animals. On average, however, YOY trips lasted 1.2 to 3.5 d longer and required up to twice as much transit time to reach foraging areas that were 1.5 to 3 times farther from haul-out sites than those of subadults and adults. This suggests an overall apparent higher foraging effort for YOY. Differences, however, were highly seasonally dependent. In all groups, apparent foraging effort decreased in the summer and increased in the winter, which is consistent with seasonal changes in prey distribution and energy content. Adult foraging patterns showed complex seasonal patterns influenced by both reproductive cycles and seasonal environmental variation, whereas annual foraging patterns of YOY and subadults, neither of which invest in reproduction, were simpler and appeared more closely tied to seasonal changes in prey availability and condition. Although foraging in the same habitats, male and female YOY showed small but significant differences in movement behaviour and trip structure. These ­differences are unlikely to be due to size difference, which is minimal at this age, and suggest that sex-related differences in foraging develop early before sexual size dimorphism is significantly expressed.

KEY WORDS: Animal movement · Ontogeny · Juvenile foraging · Foraging strategy · Optimal annual routine · Sexual segregation · Marine mammal

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Cite this article as: Breed GA, Bowen WD, Leonard ML (2011) Development of foraging strategies with age in a long-lived marine predator. Mar Ecol Prog Ser 431:267-279.

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