A DYNAMIC COMBINED ACOUSTIC AND RADIO TRANSMITTING TAG FOR DIADROMOUSFISH

A combined acoustic and radio transmitting (CART) tag employing a dyna mic conductivity switch suitable for investigating the migratory behav ior of diadromous fish is described. The unique feature of the transmi tter is its ability to sense the electrical conductivity of the ambien t water and therefore operate in the appropriate signal mode. Under fr esh water conditions the transmitter operates in radio mode; in sea wa ter it operates in acoustic mode. To optimize range performance the co nductivity threshold setting at which the tag switches mode can be cha nged to suit the application. This paper describes a proposed criterio n for threshold selection, the physical probe characteristics and the recommended tag attachment procedure.