Broadband echosounder measurements of the frequency response of fishes and euphausiids in the Gulf of Alaska

Abstract

Broadband acoustic scattering techniques are not widely used in fisheries acoustics, but this may change due to the recent commercial availability of a broadband echosounder system operating at frequencies commonly used in fisheries surveys. A four-channel (15–150 kHz) broadband echosounder was used to investigate the potential of broadband methods to improve species discrimination during a walleye pollock (Gadus chalcogrammus) survey in the Gulf of Alaska. Narrowband echosounders combined with mid-water and bottom trawls were used to identify aggregations of interest for broadband measurements. Broadband frequency responses were measured for multiple pelagic and semi-demersal fishes as well as euphausiids. No clear patterns in the broadband frequency responses were identified that would aid in discrimination among the commonly encountered swimbladder-bearing species. The results are consistent with narrowband observations and suggest that both techniques face the same challenges when attempting to discriminate among acoustically similar species as frequency responses overlap within the measured bandwidth. However, examples are presented in which broadband frequency responses provide additional information about near-resonant scatterers. The benefits of broadband operations have not been fully realized and widespread adoption of broadband techniques and improved processing algorithms may yield improved acoustic-based species discrimination for use during fisheries surveys.

Characterization of sound scattering layers in the Bay of Biscay using broadband acoustics, nets and video

“…Our results illustrate the potential of broadband acoustics to (i) fill-in the gaps between narrowbands, (ii) investigate the SSLs fine frequential heterogeneity and (iii) ascertain the presence or absence of resonance peaks [21] and derive their actual maximum backscattering intensity (Fig 4(b)). Narrow-band acoustics can lead to serious miss-interpretation when resonant peaks are present far away from the sampled frequency (Fig 4(d)).…”

“…An important step in broadband data post-processing is the choice of the Fast Fourier Transform (FFT) window width ( i.e. the amount of data points used to compute frequency spectra) [21]. Reducing the FFT window length increases the spatial resolution, but decreases the frequency resolution.…”

“…Until recently, most SSL acoustic studies were conducted using narrowband, multi-frequency acoustics [1, 14, 17]. However, the emergence of broadband acoustics [18] as standard monitoring tools has the potential to improve species identification based on their broadband frequency spectra [19–21].…”

Practical implementation of real-time fish classification from acoustic broadband echo sounder data

“…At sea practice of calibration exemplifying limited deviation gain. For example, historical calibration from Tridens II from EK60 and EK80 CW systems is shown in Figure 3 In contrast, while calibration of broadband active acoustic systems is common both at sea and in water tanks [32]- [34], experience with routine at sea calibration of systems such as the EK80 FM is lacking. This is mainly due to the difficulty in using these systems for acoustic survey purposes (large data size, processing handling).…”

We can reduce the impact of scientific trawling on marine ecosystems

“…Species identification using only acoustic data without trawling has been the focus of research for many decades (Horne 2000). Recent advances in acoustic methodology, in particular broadband techniques, are expected to allow some level of species discrimination without the need for trawl sampling but are unlikely to replace identification hauls for species which are acoustically identical (Bassett et al 2018).…”