Side-aspect target strength of Atlantic salmon (Salmo salar), brown trout (Salmo trutta), whitefish (Coregonus lavaretus), and pike (Esox lucius)

The side-aspect acoustic target strengths (TS) of 19 Atlantic salmons (Salm o salar), 16 brown trouts (Salmo trutta), 10 whitefish (Coregonus lavaretus ) and 9 pikes (Esox lucius) were measured using a 200 kHz split-beam echoso under, in order to study the relationship between TS and fish size indices (length, weight and side area). We effect of side aspect angle on TS was al so studied. Linear models between TS and the logarithm of the fish size ind ices were fitted with length being best for predicting TS. Typically, the s tandard error of estimate was 1.2-2.9 dB. The side-aspect TS measurements w ith specimens of known size showed that the linear relationship between ful l side-aspect TS and the logarithm of fish length for salmonid (Salmo salar + Salmo trutta) was on average 4.7 dB (SE = 0.7), lower than for whitefish and pike combined. The effect of side aspect angle on TS was modelled with cos(3) (2 alpha) function. The differences in the TS between full side asp ect and head/tail aspect were 17.4, 19.0 and 19.6 dB for salmonid, whitefis h, and pike, respectively. (C) 2000 Ifremer/CNRS/INRA/IRD/Cemagref/Edition scientifiques et medicales Elsevier SAS.