The aim of this paper is a better understanding of tuna behavior in captivity and the feasibility of the feeding process monitoring using non-invasive techniques. We analyze the acoustical recordings obtained with the Simrad EY500 single beam echosounder at 38 kHz, with dorsal measurements of captive Bluefin Tuna (Thunnus thynnus) kept in feeding cages from February to July 2005. The measurements were taken by the IEO (Spanish Institute of Oceanography) in the frame of the REPRODOTT (Reproduction and Domestication of Thunnus thynnus) European project, to monitor the behavior of forty specimens, placed in a sea cage (25 meters of diameter and 20 meters of high). The echosounder was placed down-looking on the sea surface in the center of the cage. From the echograms, we studied the tuna behavior (rate and average speed of passage through the transducer beam, vertical movements, etc), and the evolution of the average of dorsal target-strength (TS) during the six months feeding period at the selected frequency. The effectiveness of the physical characteristics of the echosounder (transducer type, operation frequency, etc) is discussed.
