If you've ever seen elephant seals(象海豹) lying on a beach, you might think that they're always sleeping. But in fact, they spend about seven months of the year in the ocean. So how do they sleep while they're in the ocean?
Even though elephant seals are large animals, they have to be careful in the ocean. Near the surface, some dangerous animals like sharks might attack(攻击) them. So elephant seals spend most of their time diving(下潜) deep underwater, looking for food.
To find out how they sleep in the deep, a scientist named Jessica Kendall-Bar created a special cap. She and her team put the caps on thirteen female young elephant seals. The caps recorded the elephant seals brain activities. They also collected information on the elephant seals' heart rates(心率), how their bodies were moving, and how deep they were.
The scientists learned that elephant seals sometimes sleep for a short time while they are diving. They only sleep for about 10 minutes at a time. As they begin to sleep, the elephant seals can control their bodies. But when they are deeply asleep, they simply begin to fall, spinning(快速旋转) in a circle " like a falling leaf " . The elephant seals wake up in time to go up for more air. In shallower(较浅的) areas, the elephant seals sometimes wake upon the seafloor.
Using the information they collected from the cap-wearing elephant seals, the scientists created a computer program to study older records of elephant seal trips. The scientists found that elephant seals only sleep for about two hours a day when they're in the ocean. That means that the rest on land is very important for them. Back on land, they sleep for about 10. 8 hours a day.
The scientists hope that their work will help to protect the places where elephant seals sleep when they're on land.
