Application of acoustic Doppler current profiler combined with a scientific echo sounder for krill Euphausia pacifica density estimation

Abstract

An application of the acoustic Doppler current profiler (ADCP, 153.6 kHz) in combination with a scientific echo sounder (EK60, 38 and 200 kHz) was investigated to estimate the density of krill Euphausia pacifica. The acoustic backscattering strength from sound scattering layers was compared with biomass estimates from midwater trawls. Euphausia pacifica was targeted among mixed species populations in the sound scattering layer in the offshore Funka Bay area of Hokkaido, Japan. The frequency characteristics of acoustic backscattering by krill were calculated using a distorted wave Born approximation scattering model at three frequencies. Krill aggregations identified from the EK60 data were extracted as the mean volume backscattering strength difference between two frequencies. They were then used to identify similar aggregations in the ADCP data by matching observation times and depths for the two methods, which were applied simultaneously. Results from the comparison of the mean volume backscattering strength and the density calculated from the ADCP and EK60 showed that ADCP can be used to measure density and spatial-temporal distribution of krill aggregations. Current speed and direction at the study site were found to be 16.1 cm/s and 187.0∞, respectively, and krill speed and direction (including the current component) were found to be 19.8 cm/s and 172.2∞, respectively. Based on the ADCP data, the net speed and direction of the krill aggregations were found to be 5.9 cm/s and 128.0∞, respectively.KEY WORDS: acoustic Doppler current profiler, distorted wave Born approximation model, echo intensity, Euphausia pacifica identification, krill identification, mean volume backscattering strength, scientific echosounder.

Turbulence and hypoxia contribute to dense biological scattering layers in a Patagonian fjord system

“…An alternate approach is to use acoustic techniques, which can provide high-resolution data on zooplankton DVM patterns Díaz-Astudillo et al, 2017) and segregation patterns throughout the water column (Sato, 2013;Sato et al, 2016). For instance, DVM patterns of dense krill aggregations have been detected using acoustic Doppler current profilers (ADCP) moored around the Antarctic Peninsula, the Kattegat Channel and off Funka Bay, Japan (Buchholz et al, 1995;Lee et al, 2004;Zhou and Dorland, 2004;Brierley et al, 2006). In Chilean fjords, ADCPs have been used to identify changes in vertical distribution and DVM patterns of zooplankton (e.g., from normal diel to twilight vertical migrations) over several months in the Reloncaví Fjord .…”

“…The beam-average of the AGC for the four transducers was used to obtain optimal results following the procedure in Brierley et al (2006). Finally, R is the slant range to the sample bin (m), which uses the vertical depth as a correction (Lee et al, 2004). Therefore, R is expressed as,…”

“…Consistent evidence from multiple echo-sounder surveys, ADCP moorings and semi-continuous in situ zooplankton measurements supported the existence of major circadian displacements of macrozooplankton during night hours be- , 2017). DVM is a common feature of many zooplankton groups, observed around the world using different ADCP and echosounder frequencies, e.g., at the Kattegat Channel (Buchholz et al, 1995), the northeast Atlantic (Heywood, 1996), the northwest coast of Baja California, Mexico (Robinson and Gómez-Gutiérrez, 1998), the northeastern Gulf of Mexico (Ressler, 2002), the Antarctic Peninsula (Zhou and Dorland, 2004), the Arabian Sea (Fielding et al, 2004), Funka Bay, Japan (Lee et al, 2004), south Georgia (USA), in the Atlantic sector of the Southern Ocean (Brierley et al, 2006) and Saanish Inlet, British Columbia, Canada (Sato et al, 2013). The scattering layers observed in these studies highlight the abundances of the major zooplankton species, represented by amphipods, euphausiids, siphonophores, chaetognaths, pteropods, crustaceans, small fish and gelatinous plankton.…”

Use of moored acoustic instruments to measure short‐term variability in abundance of Antarctic krill

“…Hamner and Hamner (2000) suggest numerical densities of up to 64,000 krill per m 3 are possible, and these would provoke S v values of around -20 dB. Although ADCPs can provide quantitative estimates of backscatter density in some circumstances (Lee et al, 2004), this is not the principal purpose of the instrument and they do not always deliver values directly equivalent to those obtained by scientific echosounders (Brierley et al, 1998a). This, and the fact that they cannot easily be calibrated in situ (athough we understand absolute calibration is now possible; Eberhard Fahrbach, Alfred Wegener Institut, personal communication, 2005), makes these instruments less than ideal for quantitative backscatter measurement.…”

Fish behaviour and orientation-dependent backscatter in acoustic Doppler profiler data

“…However, the existence of the backscatter data provides the attractive opportunity for use in biological surveys; see for example Flagg and Smith (1989) and Ashjian et al (1994). It is also possible to combine the velocity and backscatter data to infer fish behaviour (Demer et al, 2000;Zedel et al, 2003;Lee et al, 2004). However, proper deployment of these instruments for biological applications requires accurate calibration of acoustic backscatter, and this has proved difficult with existing systems (see Brierely et al, 1998;Ressler, 2002;Fielding et al, 2004).…”