Target strength measurements of European Anchovy (Engraulis encrasicolus L.) by the control method

Abstract

        European anchovy, Engraulis encrasicolus (L.) is an important commercial species on the Atlantic coasts northward to southern North Sea, Mediterranean, Black Sea and also Aegean Sea. Target strength (TS) is a scale factor to get abundance, but there is few TS information in terms of this kind of species. In this study we measured TS of European anchovy by the control method in the fresh water tank. The measuring system’s frequency is 38 kHz. Samples were captured in the Aegean Sea and transported with ice by air kept in the refrigerator under –40 degree in the laboratory. After defrosted TS patterns of 12 European anchovy were measured by the control method. Target strength patterns were measured as a function of tilt angle, ranging from –50 degrees (head down aspect) to 50 degrees (head up aspect) at every 1 degree. Obtained TS pattern become broad. Normalized maximum TS become –66.5 dB. Normalized average TS become –69.8 dB and –72.2 dB assuming tilt angle distribution as N(-3.4, 10.3) and N(12.0, 23.5).