The instrument closest to the head is the satellite transmitter, which tells us where the females are when they are feeding at sea. There are two instruments nearest to her tail, one is a time-depth recorder or TDR that tells us how deep she is diving, for how long and what the ocean temperature and light levels are. The other is a VHF or radio transmitter that we use to locate the females when they are back on the beach so that we can recapture the sea lion and recover our instruments.