Linking movement, diving, and habitat to foraging success in a large marine predator
Date
2006-12
Authors
Austin, Deborah
Bowen, W. Don
McMillan, Jim I.
Iverson, Sara J.
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Abstract
Establishing where and when predators forage is essential to understanding trophic interactions,
yet foraging behavior remains poorly understood in large marine carnivores. We investigated the
factors leading to foraging success in gray seals (Halichoerus grypus) in the Northwest Atlantic in
the first study to use simultaneous deployments of satellite transmitters, time depth recorders, and
stomach-temperature loggers on a free-ranging marine mammal. Thirty-two seals were each fitted with
the three types of instrumentation; however, complete records from all three instruments were
obtained from only 13 individuals, underscoring the difficulty of such a multi-instrument approach.
Our goal was to determine the characteristics of diving, habitat, and movement that predict feeding.
We linked diving behavior to foraging success at two temporal scales: trips ( days) and bouts (
hours) to test models of optimal diving, which indicate that feeding can be predicted by time spent
at the bottom of a dive. Using an information-theoretic approach, a Generalized Linear Mixed Model
with trip duration and accumulated bottom time per day best explained the number of feeding events
per trip, whereas the best predictor of the number of feeding events per bout was accumulated bottom
time. We then tested whether characteristics of movement were predictive of feeding. Significant
predictors of the number of feeding events per trip were angular variance (i.e., path tortuosity)
and distance traveled per day. Finally, we integrated measures of diving, movement, and habitat at
four temporal scales to determine overall predictors of feeding. At the 3-h scale, mean bottom time
and distance traveled were the most important predictors of feeding frequency, whereas at the 6-h
and 24-h time scales, distance traveled alone was most important. Bathymetry was the most
significant predictor of feeding at the 12-h interval, with feeding more likely to occur at deeper
depths. Our findings indicate that several factors predict feeding in gray seals, but predictor
variables differ across temporal scales such that environmental variation becomes important at some
scales and not others. Overall, our results illustrate the value of simultaneously recording and
integrating multiple types of information to better understand the circumstances leading to foraging
success.
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Citation
Austin, Deborah, W. Don Bowen, Jim I. McMillan, and Sara J. Iverson. 2006. "Linking movement, diving, and habitat to foraging success in a large marine predator." Ecology 87(12): 3095-3108. Copyright by the Ecological Society of America.