Fifty-seven elephant seals had electronic sensors placed on their heads to transmit information. The sensors fall off when the elephant seals moult and lose their fur.
The data of where the seals were going and how far they were diving were recorded every few seconds and sent back by satellite. While doing this, his seals also came up with a plethora of data on the depth of the waters surrounding the Antarctic.
I bet I know where they got that idea: