Animal-Borne Acoustic Transceivers Reveal Patterns of at-Sea Associations in an Upper-Trophic Level Predator
Date
2012-11
Authors
Lidgard, Damian C.
Bowen, W. Don
Jonsen, Ian D.
Iverson, Sara J.
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Abstract
Satellite telemetry data have substantially increased our understanding of habitat use and
foraging behaviour of upper-trophic marine predators, but fall short of providing an understanding
of their social behaviour. We sought to determine whether novel acoustic and archival GPS data could
be used to examine at-sea associations among grey seals (Halichoerus grypus) during the fall
foraging period. Fifteen grey seals from Sable Island, Canada were deployed with Vemco Mobile
Transceivers and Satellite-GPS transmitters in October 2009, 13 of which were recaptured and units
retrieved 79 +/- 2.3 days later during the following breeding season, December 2009-January 2010. An
association between two individuals was defined as a cluster of acoustic detections where the time
between detections was <30 min. Bathymetry, travel rate, and behavioural state (slow and fast
movement) were determined for each GPS archival point (3.7 +/- 0.1 locations recorded per hour).
Behavioural state was estimated using a hidden Markov model. All seals had been involved in
associations with other instrumented seals while at sea, with a total of 1,872 acoustic detections
recorded in 201 associations. The median number of detections per association was 3 (range: 1-151)
and the median duration of an association was 0.17 h (range: <0.1-11.3 h). Linear mixed-effects
models showed that associations occurred when seals were exhibiting slow movement (0.24 +/- 0.01
ms(-1)) on shallow (53.4 +/- 3.7 m) offshore banks where dominant prey is known to occur. These
results suggest the occurrence of short-term associations among multiple individuals at foraging
grounds and provide new insights into the foraging ecology of this upper-trophic marine
predator.
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Citation
Lidgard, Damian C., W. Don Bowen, Ian D. Jonsen, and Sara J. Iverson. 2012. "Animal-Borne Acoustic Transceivers Reveal Patterns of at-Sea Associations in an Upper-Trophic
Level Predator." Plos One 7(11): 48962-e48962.