Do crabeater seals forage cooperatively?
Nicholas J. Gales1, William R. Fraser2, Daniel P. Costa3 and Colin Southwell1
1Australian Antarctic Division,
2Polar Oceans Research Group,
Crabeater seals are an abundant pack-ice predator which feed almost exclusively on krill. They have a circumpolar distribution and are generally sighted hauled out on ice flows alone or in pairs. Here we report our observations of a sighting of 150-200 of crabeater seals which were synchronised in their diving and surfacing behaviour. We report on the low frequency of the sighting of such large aggregations of seals during pack-ice seal surveys. We present a summary of unpublished, similar observations of large groups of crabeater seals in synchronous dive cycles, and suggest the most plausible explanation of this behaviour is some form of cooperative foraging behaviour. We suggest that either the crabeater seals cooperate by herding krill into a denser and more contained aggregation, or they synchronise their independent foraging dives to sufficiently disrupt the krill aggregation to improve prey capture rates. Either strategy would need to confer a net advantage in the energy intake rate to each seal for it to represent a cooperative foraging mechanism. Current research on crabeater seal foraging using satellite linked dive recorders is unlikely to provide sufficiently fine-scale data to examine this hypothesis. Nor will this approach indicate if a seal is foraging with conspecifics. The use of remote or animal-borne camera systems is more likely to provide an insight into fine-scale foraging tactics, as well as the possible, occasional use of cooperative foraging strategies.
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