第46回 DO DOLPHINS SLEEP?
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Yes they do, but not in the way that land mammals, including humans sleep. The bottlenose dolphins (Tursiops truncatus) and finless porpoise (Neophocaena phocaenoides) at Kaikyokan, all display resting and sleep behaviour. Late at night when the Aquarium is closed, the dolphins and porpoise can be watched resting on the surface of the water and some of the dolphins in the Aqua-theatre also rest on the pool bottom. Exactly how dolphins sleep has been a mystery until recent studies of their brain and behaviour in Aquariums and at sea, led scientists to believe that bottlenose dolphins are capable of resting half of their brain during sleep while the other half remains conscious and alert to the environment around them. This sleep behaviour may have evolved partly in response to the need for keeping alert for predators such as sharks, for staying close to the group while resting and of course to continue breathing while at the surface. The ability for dolphins to rest part of the brain while other parts function normally is unique to cetaceans (Whales, Dolphins and Porpoises). While most studies into sleep behaviour have involved bottlenose dolphins, other species have been observed displaying similar behaviour and it is presumed that all cetaceans sleep in a similar way. |
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| At Kaikyokan, our dolphins have developed more than one sleeping pattern, which is very interesting to us because certain dolphins appear to have a preferential sleep pattern. For instance, Aruka prefers to spend a lot of her sleeping time resting on the bottom of the pool, lying in front of the large acrylic window. Sometimes, she will even get angry to other dolphins if they try to rest in the same position when she wants to rest there. Another pattern is resting at the surface in the centre of the pool and drifting (usually in circles) with the movement of the water. A third pattern involves the animals being grouped together while the water circulation carries them around the pool. During each of these sleep / resting patterns the dolphins can be observed surfacing to breathe every 1~3 minutes. As the sun rises each morning, they begin to show more energy swimming about the pool and playing, in anticipation of the daily activities.
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Curator for Marine Mammals Grant Abel |
