How pulse lengths impact fish stock estimations during hydroacoustic measurements at 70 kHz

• DOI: 10.1051/alr/2011104
• Publication Date: 2011-03-17T08:04:15Z
• Authors: Małgorzata Godlewska; Michel Colon; Adam Jóźwik; Jean Guillard
• Keywords: Target strength; Fish stock; Echo sounding; Pulse duration

Water Framework Directive requires reliable and effective monitoring tools, hydroacoustics has a potential to be one of them. The effect pulse duration on in situ acoustical estimates fish density their size distribution was investigated. Measurements were performed the oligo-mesotrophic Lake Hancza (Poland) using SIMRAD EK60 split-beam echo-sounder at 70 kHz frequency. During survey, two similar transducers pinged alternatively through multiplexer 4 different lengths, from short long ones. results show that volume backscattering coefficient (Sv) values, equivalent biomass, not influenced by length. However, number detected fish, mean target strength (TS), consequently density, differed significantly for data. This especially noticeable layer above thermocline with dense populations. In this upper layer, Sawada index frequently exceeded value 0.1 leading overestimation TS underestimation density.