ocr: SPYING AT SEA Modern technology allows us to track at-sea behavior off bearded seals without bothering them- - and without getting wet. After coloring epoxy with fuorescent dye for easy visual identification, we glue a black time-depth recorder (TDR) and al VHF radio transmitter to the fur on a seal's back (left). Every ten seconds the TDR records whether the seal is in or out of the water and how fast and deep it swims or dives, VHF trangmitters. let us keep tabs on the seals so1 we can retrieve our gear and its precious data. 134 National Geographic, March 1997
