A DYNAMICALLY SWITCHED COMBINED ACOUSTIC AND RADIO TRANSMITTING (CART) TAG - AN IMPROVED TOOL FOR THE STUDY OF DIADROMOUS FISHES

This paper describes a pilot study investigating the effectiveness of a combined acoustic and radio transmitting (CART) tag employing a dyna mic conductivity switch in monitoring the migratory behavior of adult Atlantic Salmon (Salmo salar) through an estuary environment. The uniq ue feature of the transmitter is its ability to sense the electrical c onductivity of the ambient water and therefore operate in the appropri ate signal mode. Under fresh water conditions the transmitter operates in radio mode; in sea water it operates in acoustic mode. The ability to switch between radio and acoustic modes affords the opportunity to optimize range performance, to maximize transmitter longevity and to accurately monitor the behavior of a fish moving back and forth.