Target strength ex situ of sprattus fuegensis in chilean fjords

Two experiences of target strength measurement of Sprattus fuegensis carried out through two differentiated ex situ methodological approaches “fish group” and “individual mark”. Both experiences were carried out on board of the artisanal vessel Huracan I The system used were (S1) conformed by a 38 Khz transducer (model ES38B) connected to a GPT EK 60; while the second (S2) consisted of a 38 Khz transducer (model ES 38DD) connected to a WBT EK 80. In the S1 system the fishes were introduced to a cylindrical cage armed with mesh cloth with a mesh size of 12 mm. The S2 structure was a monofilament cube of 50×50×50 cm. The specimens were kept alive ad libitum in tank with a 1 m3 water recirculation for both systems. The main results showed that: i) “S1” measurement showed a lower b20 variation in the experiments 4 and 2 with 256 μs pulse (−71.34 and −71.81; CV=3%) and 512 μs pulse (−71 and −71.43; CV=2%) respectively. Meanwhile for “S2” the measurement with 256 μs pulse obtained in the experiment 1 a b20 = −69.65 with TS= −46.42dB (CV=3%) and in the experiment 2 a b20= −70.04 and TS= −45.52(CV=3%); show a lower variation. Thus the resampling per group of length, obtains for the total a variation of TS for −46.69dB of (−46.8 and 46.5) and for the b20 total = −69.91 of (−70.03 and −69.73). It is shown that for S1 it is possible to measure target strength measurement as a shoal discounting the system's target strength, for S2 is possible an individual detection for targets resolved for the species.