In order to specify resting behaviors of dolphins in captured
condition, intensive observations were carried out at SINAGAWA
Aquarium and Minami-Chita Beach Land. Seven adult bottlenose dolphins
(_Tursiops truncatus_) and three hybrid infants were observed.
Daily activity pattern presented with breath interval and an activity index calculated from swimming speed was analyzed. In most cases, high activity was observed from 12:00 p.m. to 16:00 p.m. and low activity was observed from 0:00 a.m. to 3:00 a.m. Behavior patterns characteristic in the low activity time could be categorized into following 3 types: "Surface Rest" characterized by long immobile stay at the water surface, "Bottom Rest" characterized by long immobile stay at the bottom, and "Swim Rest" characterized by circular slow swimming near the bottom in a fixed direction. Breath interval in these behaviors was significantly longer than other behaviors. These three behaviors occupied 90 % of the low activity time (0:00 a.m.-3:00 a.m.). Though Swim Rest was most frequently observed both in the low activity time and the high activity time, Surface Rest and Bottom Rest was not observed in the high activity time. Swim Rest occupied the most part of their resting behavior and was often made in a group. In this behavior, frequency of sound emission (both pulse and whistle) was significantly lower than that of other behaviors with high-speed swimming, and the eyes, especially the eye facing inner side of the swimming circle, tended to be closed.
The mean breath interval in these behaviors decreased in the following order: Swim Rest > Surface Rest > Bottom Rest, suggesting that deepness of the rest or sleep increase in this order. Our results suggested that the dolphins flexibly change their daily activity pattern and type of resting behavior according to the situation.