Rest and activity states in a gray whale

Abstract

The behaviour of a female gray whale (Eschrichtius robustus) that had been rescued 14 months previously was recorded continuously on a video-recorder for 9 days at 'Sea World' in San Diego. On average, during the first six recording days, active wakefulness accounted for 37.9 +/- 1.7% of each 24 h; transitional stage for 17.4 +/- 1.4% and rest for 41.2 +/- 1.7%. In the rest stage the whale was lying on the bottom of the pool (13.2 +/- 1.7%) or hanging on the surface (28. 0 +/- 1.7%). During the rest stage, it was immobile most of the time and moved only for respiration. In the rest stage both eyes could be open, one eye could be open while the other was closed or, more rarely, both eyes could be closed. Characteristic jerks of the head, neck and sometimes of the whole body were observed in the whale during the rest stage. Most jerks were single and only 10% of all jerks were serial (occurring within 10 s of a prior jerk). Eyelid movements accompanied 40% of jerks. In two episodes, intense jerks followed each other continuously for 3 and 4 s and were accompanied by eyelid movements. These jerks resembled the twitches characteristic of paradoxical sleep in terrestrial mammals. During these episodes the whale was falling slowly onto its side and subsequently started to swim in the pool.

Figure 1.

Two typical rest postures in the gray whale. The animal floated motionless on the surface with its fluke resting on the bottom of the pool or lay on the bottom of the pool on its belly. In both cases the fins were clasped to the whale’s body.

Figure 2.

All transitions among stages 1, 2 and 3 (as a percentage of the total number of all transitions between stages for 6 consecutive days).

Figure 3.

Distribution of active wakefulness and rest stage in the gray whale over the 24-h period. Average for 6 days. The thick lines link the mean hourly values representing the amount of time spent in a given stage as percentage of each hour. The standard error (SE) is marked with a thin line.

Figure 4.

Distribution of two rest stages in the gray whale over the 24-h period. Average for 6 days. The thick lines link the mean hourly values representing the amount of time spent in a given stage as percentage of each hour. The standard error (SE) is marked with a thin line.

Figure 5.

Distribution of respiratory pauses in different behavioural stages in the gray whale (as a percentage of the total number of pauses documented in a given stage during two consecutive days).

Figure 6.

The states of eyes during one rest episode in the gray whale. y-Axis represents the state of each eye: 1, opened; 2, intermediate; 3, closed; 0, not seen.