Acoustical measurement of fish abundance

Abstract

The theory of echo formation provides formulas relating echo energy to physical characteristics of the target. Single-target theory (applicable to counting isolated fish) is extended to the multiple-target case relevant to schooling fish. An echo-integrator equation relates fish density to echo energy integrated over a time gate corresponding to the depth channel of interest. Parameters include the equivalent beam angle, the expected backscattering cross section per fish, equipment sensitivity, and a time-varied-gain correction factor. Variation of environmental factors (sound speed and absorption) affects the parameter values. More important is the variation of biological factors (fish behavior and physiology) which affects backscattering cross section and target strength. Verification of the echo-integrator equation, depending upon the linearity principle concerning the addition of signals from randomly distributed multiple targets, is discussed in the fisheries context. The swimbladder is the dominant sound reflector in fish having one. Accordingly, fish targets may be classified as (a) bladder closed, (b) bladder open, or (c) no bladder. Within each category, fish of the same size have similar target strengths. Target strength variation with fish size, water depth, and time is discussed. Experimental target strengths are well scattered even for nominally similar fish. Nevertheless, useful information about fish stocks can be obtained through careful application of acoustical techniques.

Determining the target strength bambood wrasse (Pseudolabrus japonicus) using Kirchhoff-ray mode

“…Hydroacoustics, a popular method for effectively gathering information on temporal and spatial fish distribution and abundance, has become increasingly sophisticated over the years (MacLennan and Simmonds, 2005). Field application of acoustic methods to estimate animal abundance requires information on the acoustic size, and the target strength (TS) or backscattering cross-section of individual organisms (MacLennan, 1990;Thiebaux et al, 1991). Moreover, fish TS is a key variable in the acoustic assessment of fish abundance (Foote, 1987).…”

Pendugaan Kelimpahan Dan Sebaran Ikan Demersal Dengan Menggunakan Metode Akustik Di Perairan Belitung

“…Penentuan panjang dan jarak antar kaki (leg) serta arah pelayaran berdasarkan pada luas daerah yang dicakup serta waktu yang tersedia seperti dikatakan oleh Johannesson & Mitson (1983). Alur pelayaran pengambilan data dilakukan dengan menggunakan bentuk transek sistematic zig-zag transect (MacLennan, 1990) yang dimodifikasi sesuai dengan kondisi perairan. Trek dimulai dari sebelah utara menuju ke bagian selatan.…”

“…Pengintegrasian hasil deteksi dilakukan oleh EY60 dengan menggunakan metode echo integrasi menurut MacLennan (1990). Pengaturan sinyal pancar EY60 pada saat survei dapat dilihat pada Tabel 1.…”

Estimating Fish Densities from Single Fish Echo Traces

“…The physical reason that many fish species are easily detected acoustically is because they have swim bladder that account for around 90 percent of their back scattering strength [5]. A theoretical foundation for the echo integration method is given in [6], and a modern software system based on echo integration is described in [7].…”