Recording dives

Depth recorders, like those that are included with some tracking devices, can tell us a lot about where and how seals catch their food.

For a start, they tell us when seals are in the water column and when they are on land. With this information, we can learn how long they spend at sea on feeding trips and how long they spend ashore between trips.

A depth recorder can be programmed to record depth every few seconds. Then scientists can learn how long a seal stays under water, how deep it goes and even whether or not it reaches the bottom of the ocean.

Australian Fur Seals tend to feed near the sea floor. They dive straight to the bottom then they travel along the bottom until they get near the end of the dive. Then they come up to the surface.

A seal mostly decides to end its dive when it starts to run out of breath. It might also end a dive if it catches a fish that it cannot swallow in one mouth-full. A seal will bring a big fish up to the surface, there, pieces can be bitten off the fish.

The graph below shows a typical dive profile. The arrows indicate the seal diving down, staying the bottom for a few minutes, coming up then staying near the surface.

diving graph 1