GPS for the oceans

ZOOLOGISTS ROUTINELYGPSGPS track animals, from albatross to zebra, using global-positioning-system () tags which then return their data via satellite. Marine biologists have a harder time of it, though, because seawater is infuriatingly opaque to radio signals. This makes it impossible either to receive signals or to transmit any data collected back to base.That does not stop people tagging sea creatures. Data collected and stored in a tag can either be sent to a satellite in bursts if the species in question is one that comes to the surface from time to time, or the tag can be dispatched on a one-way trip to the surface after a set period. A tag may also be recovered if the animal carrying it is caught by a fishing boat. (Fisherfolk are typically paid a few hundred dollars per tag returned to its home laboratory.)