Data for: Brain activity of diving seals reveals short sleep cycles at depth

Sleep is a crucial part of the daily activity patterns of mammals. However, in marine species that spend months or entire lifetimes at sea, the location, timing, and duration of sleep may be constrained. To understand how marine mammals satisfy their daily sleep requirements while at sea, we monitored electroencephalographic (EEG) activity in wild northern elephant seals (Mirounga angustirostris) diving in Monterey Bay, California, USA. In this study, we characterized the sleep patterns of northern elephant seals from land to sea. Periods of electrophysiological sleep (slow wave sleep and rapid-eye-movement sleep) were recorded in seals on land, floating in shallow water, on the ocean floor in shallow water and the continental shelf, and during open ocean drift dives. While there was considerable variation in sleep patterns across individuals, total sleep time was lowest while sleeping at sea (<2 h/day) and highest while sleeping on land (~10 h/day). We linked sleep patterns to accelerometry and the time-depth profiles of 334 free-ranging seals (514,406 sleeping dives) to reveal a North Pacific sleepscape where seals averaged only 2 hours of sleep per day. This rivals the record for the least sleep among all mammals, currently held by the African elephant (~ 2 hours per day). This integrative study of sleep in wild northern elephant seals can help identify critical resting habitats and set the stage for comparative and translational studies of sleep. This repository contains raw electrophysiological data, processed hypnograms with identified sleep states, and integrated three-dimensional motion and electrophysiology data (“hypnotracks”). We also include data related to our sleep estimation algorithm for time-depth records of adult female northern elephant seals. All animal procedures were approved at the federal and institutional levels under National Marine Fisheries Permits 496, 836, 786–1463, 87-1743, 19108, 14636, and 23188, and by the Institutional Animal Care and Use Committee (IACUC) of the University of California Santa Cruz.

Methods
See the associated code repository and manuscript (links in the Related Works section) for additional information on the methods for data collection and processing.