Resting behavior in a rehabilitating gray whale calf

We studied the behavior of a one-year old gray whale calf (Eschrichtius robustus) during its rehabilitation at SeaWorld of San Diego. Several behaviors in this whale were grouped into 3 stages: (1) active wakefulness (mean 37.9 ± 1.7% of 24 hr during 6 consecutive days) included episodes of swimming in the main pool and in the shallow channel; (2) transitional stage (mean 17.4 ±1.4%) was composed of quiescent at the surface or near the bottom and episodes of submerging and emerging to the surface; (3) rest on the bottom of the pool (mean 13.2 ±1.7%) or at the surface (mean 28.0 ± 1.7%) during which the whale was almost completely immobile. Most apneas in this calf were <3 min. The mean respiratory pauses were 29.1±0.5s (n=1615) in active wakefulness; 21.8 ± 0.5s (n=407) during series of submergings and emergings; 26.9 ± 1,4s (n=136) during quiescence at the surface, 92.5 ± 2.5 s (n = 236) near the bottom, 63.2 ± 0.9s (n=1030) during rest at the surface, and 147.4 ± 5.0s (n = 377) on the bottom. In the rest stage, one eye could be open, tightly closed, or partially open. Characteristic muscle jerks and eyelid movements were documented in this whale during the rest stage. Most jerks were single, but in several cases jerks and eyelid movements followed each other resembling twitches characteristic of paradoxical sleep in terrestrial mammals. Our data suggested that large whales might have unihemispheric, slow-wave sleep and a low amount of paradoxical sleep, which occurs without muscle hypotonia, intensive jerks, and twitches.