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Northern elephant seals (Mirounga angustirostris) do not rest on land and spend little time on the sea surface during their long migration. When do they rest then? This question was investigated by a research group led by Assistant Prof. Yoko Mitani of the Field Science Center for Northern Biosphere. Unlike dolphins and sea lions that sleep while remaining alert to their surroundings by shutting down half of their brains, the rest cycle of elephant seals during their long two to eight month migration is a great mystery. In order to shed light on their resting behavior, several juvenile elephant seals were fitted with 3D data loggers and their behavior was monitored. By measuring both their body angles and diving paths in three dimensions, the researchers discovered that the elephant seals wobble periodically as they descend on their backs and their bodies follow a downward spiral not unlike falling leaves. This diving pattern is believed to have the benefit of preventing a too rapid descent to the sea floor while they sleep and thus prevents them from unnecessarily expending energy to return to the surface to breathe. Diving deep also allows them to rest where they are less susceptible to predators. Research into the relationship between the evolution of sleep and diving behavior and how marine mammals such as dolphins and sea lions exhibit unihemispheric slow-wave sleep—sleep in which half of their brain is at rest while the other half remains alert-as compared to the bihemispheric sleep of elephant seals using data loggers is sure to demystify the lives of marine organisms in the future. Contact information:
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