Comparison of Wideband vs Narrowband Acoustic Approach to Target Strength Value on Bullet Tuna (Auxis rochei) and Bonito (Euthynnus affinis)

Abstract

Target strength (TS) is one of the main parameters for determining fish density, abundance and biomass in acoustic technique. Therefore, it is of utmost importance to obtain an accurate TS estimate and to minimize bias from its measurement. Various factors contribute to bias in acoustic TS, namely the high diversity of species, body shape, size and also frequencies used. In this paper we compare and examine the acoustic narrowband (NB) and wideband (WB) approaches to better understand the TS response to various frequencies. The use of acoustic wideband approach, is expected to perform better and be less-biased than the narrowband, which is still widely used. The measurement of bullet tuna (Auxis rochei) and bonito (Euthynnus affinis) for the same fork length (FL) size showed the power of four frequency dependent (f^4). Furthermore, a comparison between NB frequency of 200 kHz versus WB at the nearby frequencies of 190-200 kHz and 200-210 kHz showed a significant Pearson correlation value for bonito fish size range from 17-26.6 cm, whereas in the case of bullet tuna, fish had no significant correlation at alpha=0.05 for fish size range from 16.4-26 cm.