Scientists use instruments to collect data about the location and behavior of marine mammals.
The developement of these instruments is practically a science by itself. These instruments give out a signal that can be heard on a radio receiver, that can be connected to a computer to record the data. Radio transmitters can be used to indicate presence or absence at a colony. The signal can be heard when the animal is on land, and is absent when the animal is at sea. Or may be used to indicate if the animal is at the water's surface or underwater.