Growing monitoring in sea cages: TS measurements issues
Espinosa, V.; Soliveres, E.; Cebrecos, A.; Puig, V.; Sainz-Pardo, S.; de-la-Gándara, F. (Fernando)
Hydroacoustic monitoring of fish growing in sea cages needs of an accurate
relationship between fish size and target strength (TS) for every species of commercial
interest. We discuss the conditions for TS measurement in near range conditions in sea
cages for the case of the dorsal and ventral aspects of gilthead
sea bream and bluefin
tuna.
Gilthead sea bream dorsal and ventral TS distributions, obtained with a split beam
echosounder, are unimodal
and the same results are derived for single beam data
analysis when specific processing threshold criteria are applied. The expected linear
relationship between the average TS and the logarithm of fish length is only found for
the ventral case, being more accurate the uncompensated TS single beam analysis,
probably due to near range errors.
Bluefin tuna dorsal measurements performed in a fattening farm from February to July
did not show a significant variation of TS distributions, and we propose a synchronized
system of echosounder and video recordings, in order to relate target strength and
orientation and size of specific tuna in the acoustic beam. Preliminary results indicate
that only ventral TS values correlate properly with tuna size.
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