Large reptiles like crocodiles and pelagic sea turtles are often mounted with GPS located radio transmitter tracking device. The device is epoxy/resin glued onto the carapace of the turtle or rough leathery skin of the crocodile, while in a tranquilized state, scary.
http://www.seaturtle.org/tracking/?tag_id=85691http://www.seaturtle.org/imagelib/?photo=3358http://www.seaturtle.org/tagging/satellite.shtmlOne radio tag per sea turtle costs $3,000.00 USD with satellite time. The turtle has to swim with added weight on their carapace shell, thus cause hydrodynamic drag, thus a discomfort for the pelagic animal to swim.
Reptile tracking devices are made by:
Sea Mammal Research Unit, U.K, Sirtrack, New Zealand, Telonics, U.S.A., and Wildlife Computers, U.S.A.
Alejandro Fallabrino picture showing a turtle enthusiast searches for the radio tag sea turtles with a large directional Yagi-Uda antenna with reflector element and driven half wave (usually) dipole antenna:
http://www.seaturtle.org/imagelib/?photo=1781http://en.wikipedia.org/wiki/Yagi_antenna