SLEEP IN THE HARP SEAL (PAGOPHILUS-GROENLANDICA) - COMPARISON OF SLEEP ON LAND AND IN WATER

Four young harp seals (aged three to five months) were implanted with electrodes for recording electrocorticograms (ECoG) of the two hemisph eres, and electrocardiogram, electroculogram, and electromyogram of th e neck muscles. In all the seals ECoG slow waves developed simultaneou sly in both hemispheres, irrespective of whether they slept on land, o n the water surface or submerged. Slow-wave sleep (SWS) was present in animals on the water surface and submerged, while paradoxical sleep ( PS) occurred only when the animals were submerged. Breathing in SWS co uld be both regular (pauses less than twenty seconds) and intermittent (pauses lasting up to three minutes alternating with hyperventilation periods). All the PS episodes occurred during single respiratory paus es and ended by waking while the seal ascended to the water surface to breathe. Flipper movements were sometimes observed in SWS, but never in PS. The ability of harp seals to cease respiration during sleep and to sleep under water could be an adaptation to living conditons in th e freezing seas.