NARROW-BAND ACOUSTIC IDENTIFICATION OF MONOSPECIFIC FISH SHOALS

The extraction of highly discriminant features is crucial for successf ul species identification of fish shoals if backscattered narrowband s ignals do indeed contain discriminant information. Four different meth ods of feature extraction are described and applied to the same data, providing new descriptors expected to improve species identification. Echograms, amplitude probability density function (PDFs) and spectral features are used to describe acoustic images of single shoals. Image processing is used to improve signal shoal description, by taking into account the shoal structure and species-related spatial distribution. Three pelagic species are considered: sardine (Saldina pilchardus (Wa lbaum)), anchovy (Engraulis encrasicolus (L.)), and horse mackerel (Tr achurus trachurus (L.)) detected during fisheries acoustics surveys co nducted in the Bay of Biscay. A correct classification rate of 57% ove rall was found for data covering a mesoscale oceanographic environment and including seasonal variability. If space and time scales are redu ced this value increased to 98%, emphasizing the value of non-acoustic and a priori information. (C) 1996 International Council for the Expl oration of the Sea