A new underwater telemetry apparatus was tested successfully in the field to record the track of a swimming fish and the temperature of its surrounding water.
Responding to the 75KHz signals (once per second) from the base, the transponder tagged on the fish sends back responses of 50KHz, which contain temperature information, to the three receivers at the base.
The position of the fish is calculated by the computer in the apparatus and plotted by a X-Y recorder. Simultaneously, the depth and surrounding temperature of the tag are recorded.
The field tests in a lake showed that the accuracy of position recording was about ±5% and that the effective distance and angle to search a tag were ca. 600m and ca. 50° respec-tively.
Some examples of fish tracking in the field and its problems are described.