Fish tagging
Fixing a marker or electronic tag to a fish to follow where it goes, how deep it dives and how fast it grows.
Also: satellite tag, acoustic tag
Simple tags are numbered plastic markers; if a tagged fish is caught again, the place and date show how far it moved. Electronic tags record much more. Acoustic tags send a signal picked up by receivers on the sea floor or in rivers. Pop-up satellite tags ride on a shark or tuna for months, logging depth, temperature and light, then float free and send their data to a satellite. Tagging showed that Atlantic bluefin tuna cross the ocean, and it is used to track mahseer and hilsa in Indian rivers.