Brain activity of diving seals reveals short sleep cycles at depth

Abstract

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 activity in wild northern elephant seals ( Mirounga angustirostris ) diving in Monterey Bay, California. Brain-wave patterns showed that seals took short (less than 20 minutes) naps while diving (maximum depth 377 meters; 104 sleeping dives). Linking these patterns to accelerometry and the time-depth profiles of 334 free-ranging seals (514,406 sleeping dives) revealed a North Pacific sleepscape in which seals averaged only 2 hours of sleep per day for 7 months, rivaling the record for the least sleep among all mammals, which is currently held by the African elephant (about 2 hours per day).

Foraging behaviour and ecology of transient killer whales within a deep submarine canyon system

“…This might be due to seasonal differences in their occurrence and spatial distribution patterns, with males primarily occurring in Monterey Bay in the summer moulting period, and then again during the winter breeding period when transient killer whale occurrence is lowest [ 16 , 26 ]. Male elephant seals are also proficient deep divers that can dive to greater depths for longer periods of time than juvenile and adult female seals, potentially making them more difficult for killer whales and white sharks to capture [ 16 , 54 ]. However, we did receive one anecdotal report from a fisher of a group of 5 killer whales feeding on the carcass of an adult male elephant seal during the month of August in waters offshore of Año Nuevo Island, California (J. McInnes unpublished data).…”

Biologging for the future: how biologgers can help solve fundamental questions, from individuals to ecosystems

“…At the same time, inertial measurements of drifting seals provided further support for hypotheses about the functions of drift dives for resting and food processing 20 . Finally, biologgers were used to confirm that seals sleep during drift dives 21 and derive body composition estimates and ethograms at a daily scale throughout months-long migrations to test predictions from state-dependent risk aversion theory about when animals should rest and forage 22 . This three-decade research arc examining whether behavior is state-dependent throughout oceanic migrations suggests that seals in superior body condition sacrifice more profitable nocturnal foraging hours to sleep in the safety of darkness (Figure 2) 22 .…”

Time is of the essence: The importance of considering biological rhythms in an increasingly polluted world

“…These techniques can be implemented at large spatial and temporal scales, allowing the measurement of long-term biological rhythms (e.g., seasonal variation or migration) that cannot be quantified easily, or at all, in the laboratory. Similarly, biologging devices are increasingly available to record biological rhythms in suborganismal physiological traits in wild animals, as was recently shown in the measurement of brain activity and heart rate during sleep cycles in wild northern elephant seals (Mirounga angustirostris) [77]. Although these effects have been largely unexplored in chemical pollution research, key insights can be gained from the light pollution literature, in which researchers have taken advantage of remote-sensing technologies to investigate the influence of artificial light on the timing and characteristics of long-range migratory patterns [78][79][80] (Fig 2).…”