Acoustic approaches to remote species identification: a review

Noninvasive species identification remains a longterm goal of fishers, rese archers, and resource managers who use sound to locate, map, and count aqua tic organisms. Since the first biological applications of underwater acoust ics, four approaches have been used singly or in combination to survey mari ne and freshwater environments: passive sonar; prior knowledge and direct s ampling; echo statistics from high-frequency measures; and matching models to low-frequency measures, Echo amplitudes or targets measured using any so nar equipment are variable signals. Variability in reflected sound is influ enced by physical factors associated with the transmission of sound through a compressible fluid, and by biological factors associated with the locati on, reflective properties, and behaviour of a target. The current trend in acoustic target identification is to increase the amount of information col lected through increases in frequency bandwidth or in the number of acousti c beams. Exclusive use of acoustics to identify aquatic organisms reliably will require a set of statistical metrics that discriminate among a aide ra nge of similar body types at any packing density, and incorporation of thes e algorithms in routine data processing.