Characteristics of resting behavior in a one year old gray whale (Eschrichtius robustus) in captivity
O.I. Lyamin¹,², L.M. Mukhametov¹, P.R. Manger², J.M. Siegel², and O.V. Shpak¹
¹ Severtsov Inst. of Ecol. and Evol., Moscow, 117071, Russia.
² Dept. of Psychiatry, UCLA and Sepulveda VAMC, CA 91343.
We carried out the first visual observations of the resting (sleeping) behavior of a one year old female of the gray whale (Eschrichtius robustus) at "Sea World" in San Diego. The behavior of the whale was recorded continuously on a video recorder using underwater and aerial TV cameras for 9 days and then was scored visually in real time. The whale rested lying on the bottom of the pool at the depths of 3-5 m (on average 13.2±1.7% of 24-h for the first 6 days) or hanging on the surface (28.1±1.7%). In both cases, the whale was immobile most of the time, moving only during surfacing for respiration. During rest both eyes were rarely fully closed and usually at least one eye was partly open. The pattern of respiration during rest consisted of alternating respiratory pauses and periods of ventilation. 96% of all episodes of rest on the bottom were shorter than 3 min and the longest lasted 7 min. Characteristic jerks of the head, neck, and whole body, as well as eyelid movements, were documented in the whale during behavioral rest. Some of the serial jerks could be features of paradoxical (or rapid eye movement) sleep, which has been found in all studied terrestrial mammals and birds; however, the presence of this stage is still under question in Cetaceans. This data suggest that gray whales can sleep in the ocean while motionless at the surface, submerged in the depth and even lying on the seabed.
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