Scientific Echosounder Research Articles

Feeding behavior of blue whales (Balaenoptera musculus) during austral summer in northern Chilean Patagonia

Over recent decades, the feeding strategies of the blue whale (Balaenoptera musculus) in the northern Chilean Patagonia have been studied mainly through visual observation and anatomical dissection, with limited direct behavioral analyses and measurements of prey distribution due to the difficulty of sampling. Here, we investigated the foraging ecology of this species during six annual research cruises (2014–2019) in the northern Chilean Patagonia, an important feeding and nursery area. We deployed 28 sound and movement recording tags (DTAGs), attached by suction cups, to measure fine-scale behaviors of this species. In addition, from 2016 to 2019, prey density and distribution were simultaneously recorded with tag data utilizing a scientific echosounder. A total of 949 foraging dives and 3,183 feeding events were detected from movement sensors throughout more than 190 hr of data, during both day and nighttime. Blue whales exhibited both shallow and deep foraging events utilizing different strategies in response to changing conditions of prey depth and density, with foraging dives recorded continuously for the whole duration of the deployments. Whales showed a higher feeding rate at night as they foraged on shallow and dispersed krill, but they exhibited a higher rate of foraging events per dive during the day, as they foraged on deep and dense krill patches. The whales used less energetically costly maneuvers when foraging near the surface, with lower values of pitch and speed. Both strategies are consistent with optimal foraging theory, as the whales minimizing energetic costs associated with feeding while simultaneously maximizing energy intake. These results provide valuable insights into the behavioral and foraging ecology of blue whales to promote specific conservation plans in the northern Chilean Patagonia.

High-resolution acoustically informed maps of sound speed.

As oceanographic models advance in complexity, accuracy, and resolution, in situ measurements must provide spatiotemporal information with sufficient resolution to inform and validate those models. In this study, water masses at the New England shelf break were mapped using scientific echosounders combined with water column property measurements from a single conductivity, temperature, and depth (CTD) profile. The acoustically-inferred map of sound speed was compared with a sound speed cross section based on two-dimensional interpolation of multiple CTD profiles. Long-range acoustic propagation models were then parameterized by the sound speed profiles estimated by the two methods and differences were compared.

Technology of the fish abundance accounting in fish farming cages using hydroacoustic and software tools

The purpose of the work: improvement of methods of fish number accounting in growing cages and reservoirs of fish farms using hydroacoustic tools and information technologies.Methods used: solving the problem of non-contact (non-invasive) measurement of the number of fish in cages using the hydroacoustic echo integration method. Investigation of the reflective properties of fish using a calibrated scientific echo sounder with a split beam. Carrying out measurements with different numbers of fish in cage. Identification and analysis of factors affecting the accuracy of the echo integration estimation of the number of fishes in cage.Novelty: the elements of novelty are the use of a scientific echo sounder with vertically oriented antenna and split beam to estimate the number of fishes in cages, the algorithm for calculating the number of fishes in cages by the echo integration method, the results of the study of reflective properties of Amur carp and identified optimal measurement conditions that allow hydroacoustic estimates of number with maximum accuracy.Results: the dependences of target strength on the linear size of Amur carp are obtained. An algorithmic scheme for calculating the number of fishes in cages by the hydroacoustic echo integration method has been developed. Experiments were carried out with different numbers of fish in the cage. It is established that the main factors affecting the accuracy of the population estimate are the number of individuals in the cage and the daily distribution of fish. Measurements at night and at concentrations above the threshold (50 pcs./m2) can significantly bring the estimated and true numbers of fish in the cage closer and reduce the variability of density estimates.Practical significance: solving the problem of remote measurement of the fish number in growing cages will allow farmers to optimize feed needs, which, in turn, will ensure rapid growth of fish without overfilling it and not polluting the reservoir.

Evalution of the ability to infer tilt angle and size distributions of fish using a broadband scientific echosounder based on simulation

Evalution of the ability to infer tilt angle and size distributions of fish using a broadband scientific echosounder based on simulation

Monitoring Two Typical Marine Zooplankton Species Using Acoustic Methods in the South China Sea.

The broadband scientific echosounder is considered to have great potential for zooplankton monitoring. In this study, two common types of zooplankton in the South China Sea, Rhopilema hispidum and Acetes chinensis, were continuously monitored using a broadband scientific echosounder. The results revealed distinct volume scattering strength (SV) spectral characteristics between the echoes of R. hispidum and A. chinensis. Meanwhile, echoes of R. hispidum and A. chinensis were classified using the k-means clustering algorithm, achieving an 83.4% accuracy rate. The SV value at a nominal frequency of R. hispidum changes more sharply than that of A. chinensis, suggesting that the density of R. hispidum changes more dramatically. This study demonstrates the advantages of monitoring R. hispidum and A. chinensis outbreaks with a broadband scientific echosounder.

Demonstrating the relevance of spatial-functional statistical analysis in marine ecological studies: The case of environmental variations in micronektonic layers

In this study, we conducted an analysis of a multifrequency acoustics dataset acquired from scientific echosounders in the West African water. Our objective was to explore the spatial arrangement of marine organism aggregations. We investigated various attributes of these intricate biological entities, such as thickness, relative density, and depth, in relation to their surroundings. These environmental conditions were represented at a fine scale using a towed multiparameter system. This study is closely intertwined with two key domains: Fisheries acoustics techniques and functional data analysis. Fisheries acoustics techniques facilitate the collection of high-resolution spatial and temporal data concerning marine organisms at various depths and spatial scales, all without causing any disturbance. On the other hand, spatial-functional data analysis is a statistical approach for examining data characterised by functional attributes distributed across a spatial domain. This analysis encompasses dimension reduction techniques, as well as supervised and unsupervised methods, which take into consideration spatial dependencies within extensive datasets.We began by applying multivariate statistical techniques and subsequently employed Functional Data Analysis (FDA). In the modeling section, we introduced the spatial dimension with the spatial coordinates as covariates in the General Additive Model (GAM) and Functional Generalized Spectral Additive Model (FGSAM) models, aiming to underscore its relevance in those contexts. In an exploratory phase, Multivariate Functional Principal Component Analysis provided detailed insights into the variations of parameters at different depths, a capability not offered by traditional Principal Component Analysis. When it came to regression tasks, we explored the interactions between descriptors of Sound Scattering Layers and key environmental variables, both with and without considering spatial dimensions. Our findings revealed significant distinctions between northern and southern Sound Scattering Layers, as well as between coastal and high-sea regions. The use of the spatial locations enhanced the performance of GAM and FGSAM, particularly in the case of salinity, reflecting the influence of water mixing and seawater temperature. The multifaceted effects of environmental variations on Sound Scattering Layers underscore the importance of spatial-functional statistical analysis in ecological studies involving complex, spatially functional objects. Beyond the scope of this specific case study, the application of functional data analysis shows promise for a wide array of ecological studies dealing with extensive spatial datasets.

Assessing the influence of abiotic factors on small pelagic fish distribution across diverse water layers in the Northwest Pacific Ocean through acoustic methods

The Northwest Pacific Ocean is one of the most productive fisheries in the world, with small pelagic fish constituting a substantial portion of its fishery resources. Changes in abiotic factors can affect the distribution of marine fish, but there are limited studies on the relationship between abiotic factors and fish density in a vertical direction. This study used acoustic measurement data collected by the scientific research vessel “Songhang” equipped with a Simrad EK 80 scientific echosounder from June to July 2022, to estimate the small pelagic fish resource density in different water layers from 0 to 200 m. Furthermore, Generalized Additive Models (GAMs) were established for various water layers, combined with remote sensing data such as temperature (Temp), salinity (Sal), net primary productivity (Nppv), as well as latitude (Lat) and longitude (Lon) data, to analyze the influence of abiotic factors on abundance density of small pelagic fish species. The results showed that mean abundance and biomass densities estimated based on the acoustic method were 3.12×105±1.42×106 ind/n mile2 and 5768.39±26224.76 kg/n mile2, respectively. Small pelagic fish resources exhibited a predominant concentration within the 0–50 m layers and displayed a significant accumulation phenomenon near the Kuroshio Extension area in each water layer. The GAMs results indicated that abiotic factors affecting fish density vary across different water layers. Temp and Lon factors appeared in optimal GAMs for all water layers and significantly contributed to fish density. Variations in temperature lead to differences in the vertical distribution of fishery resources. Our results emphasized the necessity of exploring the relationship between abiotic factors and fish density within different water layers. This research can provide scientific support for developing and managing fishery resources in the Northwest Pacific Ocean.

Long range acoustic detection of gas bubbles in a shallow water coastal environment

As the world economy moves to net zero carbon dioxide (CO2) emissions, carbon capture and storage (CCS) is recognised a mitigation mechanism in the suite of technology options. Liquified CO2 injection into offshore subsea reservoirs will be one of the CCS strategies used. Despite being improbable, CO2 leaks could occur and impact the effectiveness of this CO2 mitigation option and undermine confidence in its use as part of the suite of tools to combat climate change. To satisfy public safety expectations and environmental regulatory requirements, long-term measurement, monitoring, and verification (MM&V) plans that are affordable will be needed as part of any commercial CCS operation. Active acoustic methods are a well-suited technique as they can detect gas bubbles in the water column at extremely low flow rates. A bespoke detection system, the Echosounder Detection of Gas Events (EDGE) was developed with the goals of long-duration monitoring and detection of low flow gas bubble releases at long ranges; the literature suggests flow rates of <2 L min−1 will be readily detectable using active acoustics, well below the upper limits of a release of 1 % of stored CO2 over a 1000 year timeframe proposed by IPCC (2005). The EDGE system was housed on a seafloor lander with a battery powered scientific echosounder connected to a narrow-beam horizontally orientated transducer mounted on a turret that rotates through 360 deg. The effectiveness of the EDGE system was tested in a range of weather conditions during two six-month deployments in ∼ 20 m depth at a proposed CCS storage site, CarbonNet, situated off the coast of Victoria, Australia. Separate experiments with controlled gas releases were conducted at a local site at Hobart, Australia to establish the detection capability at range for low flow rates. These experiments found very small gas-releases (< 2 L min−1) could be detected at ranges of up to 378 m. The ability of long-term deployment of the EDGE at the proposed CCS site and the local experiments establishing range-detection ability have demonstrated that active acoustic systems can meet the dual objectives of sustained and wide-area monitoring as a key part of an aquatic based MM&V framework.

Comparative analysis of day and night micronekton abundance estimates in west Pacific between acoustic and trawl surveys

Micronekton organisms are a central component of the trophic organization in the pelagic ecosystem, being prey to top predators and participating in the export of carbon from the surface to the deep layers. Despite their importance, the abundance estimates and species distribution of micronekton remain largely uncertain. This study aimed to compare and assess two sampling methods classically used for the estimation of micronekton abundance in mesopelagic acoustic scattering layers: scientific echosounder and trawl sampling. Measurements of 38 and 70 kHz hull-mounted echosounders were examined with biological trawl samples from 8 surveys in the South-West tropical Pacific. A model of acoustic observation was built from the trawl sampling species composition and forward scattering models. Predicted and observed acoustic responses are compared to assess the variability and the difference between the acoustic and trawl sampling methods in various scattering layers, for day and night periods. The difference between methods decreased with depth and with increasing abundance of fish with swimbladders caught in trawls. Notably, this difference was found to be minimal in the nocturnal deep scattering layer (mesopelagic zone, depth>200 m). This study emphasizes potential lower estimates of organisms’ abundance by trawling and a bias towards mesopelagic fish. Understanding the differences between methods and their variability within different scattering layers is essential for studying micronekton and improving the precision of biomass estimates.

Vertical structure characterization of acoustically detected zooplankton aggregation: a case study from the Ross Sea

Acoustic data were collected by means of Simrad EK60 scientific echosounder on board the research vessel “Italica” in the Ross Sea during the 2016/2017 austral summer as part of the P-Rose and CELEBeR projects, within the framework of the Italian National Research Program in Antarctica (PNRA). Sampling activities also involved the collection of vertical hydrological profiles using the SBE 9/11plus oceanographic probe. Acoustic data were processed to extract three specific scattering structures linked to Euphausia superba, Euphausia crystallorophias and the so called Sound-Scattering Layers (SSLs; continuous and low-density acoustic structures constituted by different taxa). Four different sectors of the study area were considered: two southern coastal sectors (between the Drygalski Ice Tongue and Coulman Island), a northern sector (~30 nmi East of Cape Hallett) and an offshore one spanning about 2 degrees of latitude from Coulman Island south to the Drygalski Ice Tongue. The vertical structure of each group in each area was then analyzed in relation to the observed environmental conditions. Obtained results highlighted the presence of different vertical structures (both environmental and acoustic) among areas, except for the two southern coastal sectors that were found similar. GAM modelling permitted to evidence specific relationships between the environmental factors and the vertical distribution of the considered acoustic groups, letting to hypothesize the presence of trophic relationships and differences in SSL species composition among areas. The advantages of acoustic techniques to implement opportunistic monitoring strategies in endangered ecosystems are also discussed.

Quantitative processing of broadband data as implemented in a scientific split‐beam echosounder

Abstract The use of quantitative broadband echosounders for biological studies and surveys can offer considerable advantages over narrowband echosounders. These include improved spectral‐based target identification and significantly increased ability to resolve individual targets. An understanding of current processing steps is required to fully utilise and further develop broadband acoustic methods in marine ecology. We describe the steps involved in processing broadband acoustic data from raw data to frequency dependent target strength () and volume backscattering strength () using data from the EK80 broadband scientific echosounder as examples. Although the overall processing steps are described and build on established methods from the literature, multiple choices need to be made during implementation. To highlight and discuss some of these choices and facilitate a common understanding within the community, we have also developed a Python code which will be made publicly available and open source. The code follows the steps using raw data from two single pings, showing the step‐by‐step processing from raw data to and . This code can serve as a reference for developing custom code or implementation in existing processing pipelines, as an educational tool and as a starting point for further development of broadband acoustic methods in fisheries acoustics.

Acoustic scattering properties of a seagrass, Cymodocea nodosa: in-situ measurements

Abstract Marine prairies play various crucial roles in marine ecosystems. The seagrasses that compose them are one of the most important components engineering the marine coastal system, providing significant spatial niches. Some of the seagrasses found in marine prairies are protected, and it is not recommended to sample them with destructive methods. Non-destructive methods such as remote sensing have been proposed as important means of studying these protected species. In the present study, the acoustic scattering properties of Cymodocea nodosa were studied with two different in/ex situ experiments conducted on a Turkish Mediterranean coast using a scientific echosounder (206 kHz split beam transducer) in different months over the years 2011 and 2012. After a series of acoustic processes, correlations and regression equations were established between different acoustic parameters of the Elementary Distance Sampling Units and biometric traits of below/above ground parts of the seagrass. The relationships were logarithmically established producing first a Rayleigh zone, followed by a geometrical zone that occurred with increased biometrics. No seasonal difference occurred in the relationships for the above-ground parts. Unlike the leaves, seagrass sheaths demonstrated unstable echo energy, inconsistent relationships, and unexplained acoustic responses over the span of several months. Regarding leaf density changing in time, significant relationships were explained as a function of the acoustic zones. Four points were highlighted to explain the differences in the estimations between the two experiments; i) the backscattering strengths depended on strength of biomass and its fractions (leaf area, shoot density and volume) between the two experiments, ii) the first experiment measured backscattering strength from individual specimens, but the second experiment was performed on the total biomass of seagrass per unit area, iii) different frequency response to the biometrics occurred in the two experiments, and iv) the non-linear effect of the sheath could not be separated from that of the leaf during the second experiment. The present study was the first attempt to characterize relationships between the biometric and acoustic backscattering properties of C. nodosa, and will guide researchers in future use of non-destructive methods.

Target strength of Nile tilapia (Oreochromis niloticus) from 200 kHz calibrated fish finder and scientific echosounder: laboratory measurement and modeling

Target strength (TS) values from laboratory measurement and TS values from the model were measured and calculated from Nile tilapia (Oreochromis niloticus). Nile tilapia is one of the fastest growing aquaculture species, the fourth most produced fish globally, easily available in various sizes and lengths, and more importantly, it has a one-chambered swimbladder, which is suitable for TS measurement and modeling. The most common technique of measuring fish TS is utilizing a scientific echosounder. However, this instrument has a low implementation for small-scale fisheries due to its relatively high cost compared to the conventional fish finder. Thus, the objective of this study is to offer a solution that considers the instrument’s cost and usefulness using calibrated fish finder and scientific echosounder. TS values were produced by the two instruments that later being examined with TS from the Kirchhoff-ray mode (KRM) model to validate the result. Two single-beam echosounder instruments (Furuno FCV-628 fish finder and Simrad EK15 scientific echosounder) operated at a frequency of 200 kHz were used to assess the TS values for 30 samples of living Nile tilapia whose total length (TL) was in a range of 6 to 26 cm. In conclusion, statistically, the results showed no significant differences in TS measurement between the two instruments compared to TS values from the model. The TS values from the KRM model agreed well based on the regression analysis with the TS values from both instruments in the laboratory measurement.

Unveiling the bathypelagic zone with an acoustic vertical profiler

There is a growing interest in the study of mesopelagic and bathypelagic species due to their implication in the active carbon flux and climate change. Underwater acoustics is one of the most efficient methods to study such widely distributed communities. However, there are several challenges among which the reduced spatial resolution with depth for vessel-mounted echosounders stands out. The increase in sampling volume with range precludes observation of fine structures within the scattering layers or the study of less-aggregated organisms far from the transducer face. Echosounders are thus increasingly being deployed in alternative platforms that get the transducer close to the layers of interest. We present here the comparison between two active acoustic platforms used to analyse mesopelagic and bathypelagic species: a vessel-mounted EK60 scientific echosounder and a 6000 m depth rated Acoustic Zooplankton Fish Profiler (AZFP) attached to a CTD rosette. Both systems depicted similar vertical distributions and scattering at 38 kHz for the main scattering layers recorded around the Canary Islands but the finer vertical resolution of the AZFP discerned a series of sub-layers within them that differed in scattering, avoidance and sparsity. The availability of high frequencies at depth also provided further insights on the frequency response of those layers. However, the horizontal orientation of the AZFP created sidelobe artefacts close to the surface and bottom that limit its use in those areas. Signal-to-noise ratio of the AZFP system in the bathypelagic zone also precludes applying echointegration analysis at those depths or outside the denser scattering layers. Finally, the visualization of horizontal or temporal patterns such as migration or mesoscale features is limited to a coarse resolution using data from closely spaced successive stations. New challenges encountered with vertically-deployed echosounders and recommendations for their use are pointed out. Although no scattering layers were detected in the bathypelagic zone, this study unveils an area never before recorded acoustically.

Schrödinger's fish: Examining the robotic observer effect on pelagic animals

AbstractRobust sampling of animals is necessary for understanding ocean ecology, but evaluating the effectiveness of our samplers is a challenge. Scientific echosounders were added to two robotic platforms carrying video imaging systems: a remotely operated vehicle (ROV) and an autonomous underwater vehicle (AUV). The vehicles were used to quantitatively sample midwater life in Monterey Bay along horizontal transects at incremental depths ranging from 25 to 1000 m. The echosounders allowed the bulk behavioral responses of animals to be observed up to 200 m forward of each platform. These responses observed included no response, continual avoidance, avoidance to a fixed range resulting in a patch, and attraction. There were strong and interacting effects of depth and platform type on behavioral responses. Measurements of acoustic backscatter showed that animals responded more strongly to the AUV than the ROV. During AUV surveys, there were effects of day/night and the use of artificial illumination on animal responses. Behavioral responses to our sampling were both species‐ and context‐dependent. These data inspired the expansion of an existing mathematical framework that formalized the processes affecting the sampling of motile ocean organisms. Originally developed for net sampling, we generalized the equations to be platform‐ and sensor‐agnostic and incorporated animal decision‐making processes to allow for behaviors consistent with the full range of responses we observed. These results and the framework can help move toward more effective sampling of motile animals in the ocean.

Acoustic scattering properties of seagrass: In/ex-situ measurements of Posidonia oceanica

The marine prairies are paramount to the marine ecosystem playing a crucial role in various ways. Owing to the global atmospheric events inducing hydrospheric changes, marine seaweeds have been negatively affected and are vulnerable. Conventional methods (SCUBA), which were previously used to collect seagrasses, have become a destructive method for deriving unrecoverable damages for their stocks and have been replaced with remote sensing methods. Considering the advantages of the acoustic methods, two different in/ex-situ experiments were conducted to ground-truth the common seagrass, P. oceanica, in time and space of the Turkish Mediterranean water in 2011-2012 using a scientific echosounder with a split beam transducer operated at a frequency of 206 kHz. After the separation of the seagrass from spurious scatterers, the acoustic parameters (Sa: area backscattering strength, Sv: volume backscattering strength, and TS: Target Strength) were correlated and regressed with the biometric variables (Leaf Area Index, biomass, volume, length, width, diameter, or thickness) of different parts (leaf, rhizome, and sheath) of the seagrass. Estimation of biometrics by acoustic methods has been considered a challenge up to now. Statistical relationships between biometrics and acoustics were precisely examined for the species. The relationships were linearly established in the acoustic geometric region. There was a seasonal difference in the relationships. Their rhizomes and sheaths were considered unstable non-linear parts and remained unexplained for the acoustic response. Acoustic response to the leaf density (d, g cm-3), which was a distinguished component in the reflection, was found to be dependent on the seasonal biological activities of P. oceanica. Posidonia, which has a d greater than 1 g/cm3, produced the geometric region. The present study was the first attempt to establish the relationships of the seagrass under protection, and can decrease usage of destructive methods for future studies.

First descriptions of diurnal pelagic aggregations of the Argentine red shrimp (Pleoticus muelleri) using a broadband echosounder operating at multiple frequencies

This is the first description of diurnal pelagic aggregations of the bottom-dwelling Argentine red shrimp (Pleoticus muelleri) registered with a broadband scientific echosounder. A pelagic trawl net and an underwater video camera were used to validate all the information presented in this paper. Shrimp aggregations were characterized by increasing frequency response, more evident at frequencies greater than 120 kHz. Identification of the acoustic signature of this resource is of particular interest for the development of new methodologies to complement the traditional swept area method of estimation.

Scientific echosounder data provide a predator’s view of Antarctic krill (Euphausia superba)

Raw acoustic data were collected in East Antarctica from the RSV Aurora Australis during two surveys: the Krill Availability, Community Trophodynamics and AMISOR Surveys (KACTAS) and the Krill Acoustics and Oceanography Survey (KAOS) in the East Antarctic (centre coordinate 66.5° S, 63° E). The KACTAS survey was conducted between 14th to 21st January and 2001, and the KAOS survey was conducted between 16 January and 1 February 2003. We examine the Antarctic krill (Euphausia superba) component of these surveys and provide scientific echosounder (EK500 and EK60) data collected at 38, 120 and 200 kHz, cold water (−1 °C) echosounder calibration parameters and accompanying krill length frequency distributions obtained from trawl data. We processed the acoustic data to apply calibration values and remove noise. The processed data were used to isolate echoes arising from swarms of krill and to estimate metrics for each krill swarm, including internal density and individual swarm biomass. The krill swarm data provide insights to a predators’ views of krill distribution and density.

Fish Stock Status Assessment in Alue Naga Waters Using A 200 Khz Single Beam Echosounder

Monitoring fish stocks is an important part of sustainable management of fisheries resources. Conducting the current evaluation is very difficult since there are no reliable data on the potential for fisheries in the waters surrounding Banda Aceh city. The hydroacoustic method was used for the first time in the waters of Alue Naga, located north of Banda Aceh, to evaluate the condition of fish stocks. A single beam scientific echosounder with a frequency of 200 kHz was used to collect hydroacoustic data in the area. The collected data was then processed using the Sonar5-Pro software. Cell integration was carried out at an interval of 10 meters vertically with an elementary sampling distance (ESD) of 200 m. While the volume backscattering strength (SV) value tends to be the highest in intermediate layers, the target strength (TS) value was found to be maximum in deeper layer, reaching a maximum value of -49.46 dB at a depth of 51–60 m. Area density value (#.ha-1) was found to be the highest at a depth of 11-20 m, while Biomass (g.ha-1) at a depth of 21-30 m was the highest among other depth layers with a value of 1558 g.ha-1. According to the in-situ catches of Carangoides, Selaroides, Aphareus, Variola, and Priacanthidae, there are a number of potential reef fish resources in the waters of Alue Naga. The findings of this study strongly support the conclusion that the hydroacoustic method effectively provides comprehensive information on the horizontal and vertical distribution of fish in Alue Naga waters.

Characteristics of Sound Attenuation by Individual and Multiple Fishes

Fish biomass and stock assessment are estimated from acoustic volume backscattering strengths (Sv) obtained from various hydroacoustic equipment. Although sound attenuation due to fish schools and water influences the Sv value, only attenuation from water is considered during the acoustic data process. For these reasons, it is necessary to understand the characteristics of sound attenuation by fish. Unfortunately, little is known about sound attenuation from fish. In the present study, the attenuation from one to four fish specimens was precisely measured during ex situ experiments in a water tank. The scientific echo sounder of a split-beam 200 kHz transducer and a miniature hydrophone were used for the attenuation measurements. Results show that the maximum attenuation coefficient (α) was approximately 25 dB/cm when the 4 multiple fishes had high fish heights. The relationship between the attenuation coefficient (α200kHz) and the total fish height (Htotal) was approximately α200kHz=0.54∗Htotal ± 0.06 (r2=0.72). This work describes the sound attenuation characteristics to provide basic information for the compensation of Sv from fish schools or layers.