A dynamic combined acoustic and radio transmitting tag for diadromous fish

Abstract

A combined acoustic and radio transmitting (CART) tag employing a dynamic conductivity switch suitable for investigating the migratory behavior of diadromous fish is described. The unique feature of the transmitter is its ability to sense the electrical conductivity of the ambient water and therefore operate in the appropriate signal mode. Under fresh water conditions the transmitter operates in radio mode; in sea water it operates in acoustic mode. To optimize range performance the conductivity threshold setting at which the tag switches mode can be changed to suit the application. This paper describes a proposed criterion for threshold selection, the physical probe characteristics and the recommended tag attachment procedure.