PLOS ONERESEARCH ARTICLE

Calibration of commercial fisheries echosounders using seabed backscatter for theestimation of fishery resources
Yanhui Zhu ID1*, Minami Kenji1, Tsutomu Tokeshi2, Yoshihiro Nishiyama3, Akinori Kasai3,
Mitsuhiro Matsuura4, Hikari Horie5, Kazushi Miyashita1

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1 Field Science Center for Northern Biosphere, Hokkaido University, Hakodate, Japan, 2 Faculty of Marine
Science and Technology, Fukui Prefectural University, Obama, Japan, 3 Marine Electronic Products
Division, Furuno Electric Co., Ltd., Nishinomiya, Japan, 4 Agriculture and Fisheries Department, Miyazaki
Prefectural Advanced Fisheries Training Institute, Miyazaki Prefectural Government, Miyazaki, Japan,
5 Agriculture and Fisheries Department, Fisheries Administration Division, Miyazaki Prefectural Government,
Miyazaki, Japan* zhuyanhui920817@gmail.com

Abstract
OPEN ACCESS
Citation: Zhu Y, Kenji M, Tokeshi T, Nishiyama Y,
Kasai A, Matsuura M, et al. (2024) Calibration ofcommercial fisheries echo sounders using seabedbackscatter for the estimation of fishery resources.
PLoS ONE 19(5): e0301689. https://doi.org/
10.1371/journal.pone.0301689
Editor: Vitor Hugo Rodrigues Paiva, MARE –Marine and Environmental Sciences Centre,
PORTUGAL
Received: June 5, 2023
Accepted: March 20, 2024
Published: May 10, 2024
Peer Review History: PLOS recognizes thebenefits of transparency in the peer review
process; therefore, we enable the publication of
all of the content of peer review and author
responses alongside final, published articles. The
editorial history of this article is available here:
https://doi.org/10.1371/journal.pone.0301689
Copyright: © 2024 Zhu et al. This is an open accessarticle distributed under the terms of the Creative
Commons Attribution License, which permits
unrestricted use, distribution, and reproduction inany medium, provided the original author andsource are credited.
Data Availability Statement: All relevant data arewithin the manuscript and its Supporting
Information files.

Acoustic methods are often used for fisheries resource surveys to investigate fish stocks ina wide area. Commercial fisheries echo sounders, which are installed on most small fishingvessels, are used to record a large amount of data during fishing trips. Therefore, it can beused to collect the basic information necessary for stock assessment for a wide area andfrequently. To carry out the quantification for the fisheries echo sounder, we devised a simple method using the backscattering strength of the seabed to perform calibration periodically and easily. In this study, seabed secondary reflections were used instead of primaryreflection because the fisheries echo sounders were not equipped with a time-varied gain
(TVG) function, and the primary backscattering strength of the seabed was saturated. It wasalso necessary to use standard values of seabed backscattering strength averaged over acertain area for calibration to eliminate some of the effects of differences in seabed sedimentand vessel motions. By using standard values of the seabed secondary reflections, the fisheries echo sounder was calibrated accurately. Our study can provide a reliable framework to
calibrate commercial fisheries echo sounders, to improve the estimation and managementof fishery resources.

Introduction
According to the United Nations Convention on the Law of the Sea, the primary management
objective of marine fisheries resources is not to deplete resources by fishing and to implement
effective management measures to maintain or restore the resources to levels above the maximum sustainable yield (MSY) [1]. However, half of Japan’s fishery stocks are below the MSY
level, and about two-thirds are being over-exploited [2]. One of the reasons why most ofJapan’s fishery resources are being depleted is that it is difficult to estimate fishery stocks and

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Funding: The project funded the study forestablishing a network of environment andfisheries information, Japan Fisheries Researchand Education Agency. The funding agency has
roles in study design; in the report’s writing and in
the decision to submit the article.
Competing interests: The authors have declaredthat no competing interests exist.

Calibration of fisheries echo sounders using seabedresource management carried out based on fishery information is inefficient [3]. Therefore,
focusing on fisheries-independent surveys and the appropriate management of fisheryresources based on scientific results is necessary.
In Japan, acoustic methods are often used in fisheries resource surveys, as they can efficiently estimate biomass over a wide area. Most currently applied acoustic methods employ
quantitative echo sounders on board government and research vessels [4]. Although quantitative echo sounders can estimate the backscattering strength of an object, they have several disadvantages, e.g., the echo sounders have limited survey coverage because they are generally
installed on large vessels and have limited survey numbers because they require specialized
knowledge [5]. Due to these reasons, there has not been much progress in continuous andwide-area fisheries resource surveys using acoustic methods [5]. Therefore, there is a strong
need to improve data acquisition methods to ensure that the necessary basic information canbe collected over a wide area and frequently for the appropriate assessment of fisheryresources.
In this study, we considered using commercial fisheries echo sounders (hereinafter referred
to as ‘general echo sounders’) installed on most fishing vessels, instead of quantitative echosounders to survey fisheries resources. Notably, if general echo sounders could be used like‘quasi’ quantitative echo sounders, resource surveys could be conducted using fishing vessels,
which would greatly advance the evaluation and management of fishery resources and avoid
the cost of equipping new vessels with quantitative echo sounders. To attribute quantifiability
to general echo sounders, it is important to compensate for the strength of the reflected sound.
Therefore, it is essential to calibrate the transducer system that is processing the sound wave
[6]. In addition, it is important to periodically check the accuracy of the transducer system,
because it is used for long periods in a constantly rough environment. Therefore, to conduct
resource surveys using general echo sounders, it is necessary to establish a simple calibration
method that allows for the periodic calibrations of transducer systems.
Generally, the calibration of echo sounders is performed using a calibration ball, a standard
target with known scattering strength [6]. However, this method is a time- and manpowerintensive calibration method because the calibration ball must be placed on the sound axis of
the transducer and worked onboard [7]. For these reasons, carrying out periodic calibrations
on fishing vessels takes much work. Therefore, in this study, we considered a direct calibration
method using the seabed, which does not change significantly temporally or physically, insteadof a calibration ball. Calibration methods using seabed backscattering strength have only beenvalidated with scientific echo sounders such as split-beam and multi-beam and only primaryreflections on the seabed were used [8–11]. Since there is little verification with general echosounders, which are single beams, it is necessary to examine the validity of the calibration
method using the seabed with general echo sounders. In addition, it is also important to consider not only primary reflections on the seabed but also secondary reflections.
The standard value for calibration using the seabed is the backscattering strength in a given
area measured with a calibrated general echo sounder. When the fishing vessel has the opportunity to pass over this area where a standard value has been established, the backscatteringstrength of the seabed can be measured in the same manner. If it is almost equal to the standard value, the transducer system of the general echo sounder can be calibrated, with noanomalies. Thus, measuring the backscattering strength of the seabed allows for the easy calibration of the transducer system. From the above, in this study, we aim to demonstrate thatthe acoustic backscattering strength of the seabed can be used to calibrate general echo sounders directly.

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Methods
Mechanisms of general echo sounders
Conventional general echo sounders are generally used to detect fish schools. However, in
recent years, the time-varied gain (TVG) function has been incorporated into the received echoes of general echo sounders (Fig 1). Therefore, the backscattering strength of the object targets can be calculated from the echoes obtained by a general echo sounder. Note that the TVG
function is to compensate for the range dependence of the echo [12–14]. When echoes propagate through seawater, they undergo spherical spreading and absorption attenuation. Sphericalspreading is the attenuation due to spherical diffusion, with the characteristic of R-2 for therange R (m). Absorption attenuation is the attenuation due to energy absorption by seawater’s
components. It is exponential with the 10(-αR/10) characteristic for the absorption attenuation
coefficient α (dB/m). Unlike the general echo sounder, the TVG function is included in themain unit of the quantitative echo sounder. Therefore, the echoes obtained from the quantitative echo sounder are the values after the TVG calculation. This is the characteristic difference
between quantitative and general echo sounders.
In this study, we used the general echo sounders manufactured by FURUNO, which did
not have a function to automatically calculate the received echo level of the target. The output
data of the general echo sounders were the log conversion data (with the digit values being
0–255), proportional to the reception voltage level. The following equation was used to convert
the log conversion data into the received echo level (EL, dBμV).

EL ¼ digit � ða þ aÞ;ð1Þ

Fig 1. The imagery of general echo sounder evolution. Traditional general echo sounders could only capture fish signals. However, current general echosounders can calculate backscattering strength by adding the TVG function to those fish signals. R is the range, SV is the volume backscattering strength formultiple targets, and TS is the target strength for a single target.
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where a is the specific coefficient of each transducer at the time of log conversion, and a’ is a
specific coefficient that includes each transducer’s frequency and temperature variation characteristics. By adding the distance attenuation level, acquired from the TVG calculation to thereceived echo level, we accurately calculated the acoustic backscattering strength of the targets.
Since the TVG function differs for single and multiple targets [6], 40logR was used for singletarget calculations and 20logR for multiple-target calculations in this study.
Target strength TS (dB re 1 m2, hereinafter referred to as dB) is a logarithmic measure of
the ts, which is the proportion of the incident energy that is backscattered by a single target.
The ts is normally described using the backscattering cross-section σbs (m2) and distance R(m) from the target [15–17]. The scattered sound pressure wave Pts (Pa) from the target
returns to the transducer under the influence of two types of attenuation and beam pattern.
Then, the transducer converts scattered sound signals into electrical signals and sends them tothe preamplifier. In the preamplifier, the receiver sensitivity M (V/Pa) and the gain of thefront-end amplifier GR are used to output the voltage Ets (V). The Ets from a single target at
propagation distance R can be as2

Ets 2 ¼ ðPo M GR Þ R 4 10ð 2aR=10Þ b4 sbs =R2 :ð2Þ

Where Po (Pa) is the incident transmission sound pressure amplitude at the reference range
from the transducer front, b is the beam pattern (function of direction θ describing the amplitude sensitivity). The ‘PoMGR’ is called the factor of transmit and receive (denoted by KTR),
which depends on the transducer used and is determined by calibration [7,18]. The TVG calculations of the distance attenuation items included in Eq (2) yield a logarithmic distance characteristic of 40logR + 2αR [13,19]. Using this distance characteristic to decibel-converted Eq(2), we calculated the TS using the following equation.
TS ¼ EL

KTR þ 40logR þ 2aR;

ð3Þ

where TS is 10 log σbs/R2, EL is 10 log Ets, and KTR is 10 log KTR. This equation is the basic
general echo sounder equation to calculate the echo of an individual target [20].
When calculating the volume backscatter strength SV (dB re 1 m-1, hereinafter referred toas dB) of the group echoes, as there were multiple targets, the voltage Esv (V) was attributed to
the group echoes synthesized into the backscattering volume V (m3) for the distance R [21],which can be expressed as follows,2

Esv 2 ¼ ðPo M GR Þ R 4 10ð 2aR=10Þ V sv :

ð4Þ

Where sv (m-1) is the volume backscattering coefficient. The backscattering volume V (m3),which is the shell thickness multiplied by the effective cross-sectional area of the beam, was calculated from the volume element of thickness cτ/2 [22], using the pulse width, τ, sound speed,c (m/s), and a two-way equivalent beam solid angle of a transducer, C as
V ¼ C R2 ct=2:

ð5Þ

Substitute Eq (5) into Eq (4), a logarithmic distance characteristic of 20logR + 2αR was
obtained [10,23]. Using this 20logR TVG correction, we calculated the SV using the following
equation,
SV ¼ EL

KTR þ 20logR þ 2aR

10 logðC ct=2Þ:ð6Þ

Where SV is 10 log sv, EL is 10 log Esv.
Additionally, as sv was proportional to the distribution density per unit volume, the final
value used in the resource calculation was considered as the distribution density per unit area

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4 / 20PLOS ONECalibration of fisheries echo sounders using seabedbackscatter coefficient (sa, m2/m2). This quantity is a measure of the energy returned from alayer between two ranges and defined as the integral of sv concerning depth through the layer[24]. It can be expressed by the following equation,
Z R2
sa ¼
dR sv ¼ n ts:
ð7Þ
R1

Where R1 and R2 represent the lower and upper ranges of the volume over which sv is being
integrated. Dividing the calculated sa value by the ts, the number of the target species ‘n’ is calculated, and the distribution density per area within a specific sea area is also obtained [25].
The log measure of sa, area backscattering strength Sa (dB re 1 m2/m2, hereinafter referred toas dB), is also often used to estimate fish abundance.

Survey area and investigation
In this study, the survey was conducted in the coastal waters of Shimaura Island, Miyazaki,
Japan, from 3 July 2020 to 6 July 2020, using the medium-sized purse seiner vessel Kakutomaru. In addition, we decided to use a quantitative echo sounder at the same time to verify themeasurement results of the general echo sounder. We used a general echo sounder (FCV1500L, 15/200 kHz) manufactured by Furuno along with a quantitative echo sounder(KSE300, 38/120 kHz) manufactured by Sonic (Table 1). Note that the general echo sounder,
which is a single beam, was set to a strong transmit power even at high frequency to capture
fish school responses in deeper waters. In the case of the general echo sounder, which is a split
beam, the transmit power at a higher frequency was lower than at a lower frequency to avoid
nonlinear effects.
The survey area was near the fishing port, where fishing boats pass often, and the survey
focused on the flat seabed, where the sediment and slope had not changed significantly (Fig 2).
The flat seabed was chosen because the seabed backscattering strength is more stable on a relatively smooth seabed than on a rough seabed [26]. The survey lines were set perpendicular or
horizontal to the coast, and each measurement line was approximately 1.5 km long. We considered a total of 6 measurement lines in this study and the depth of the survey area wasapproximately 5 m at the shallowest sites and 30 m at the deepest sites (Fig 2).
In the procedure adopted in this study, we first calibrated the general and quantitative echosounders, using a calibration ball (a diameter of 38.1 mm tungsten carbide ball), before carrying out acoustic measurements. Since it was necessary to place the calibration ball directly
under the transducer, the survey was conducted in an inner bay where waves, wind, and currents were few. The mean wind speed on the day of the survey was 1.6 m/s, and the vessel wasanchored from the bow and stern to prevent the vessel from being swept away. During
Table 1. Settings for the general and quantitative echo sounders used in this study.
Specification
General echo sounderTransducer

FCV-1500L

Quantitative echo sounder
T-178

T-182

Frequency (kHz)

15

200

38

120

-3 dB beam width (˚)

32

6

8.5

8.5

Transmit power (kw)

1

2

3

1.5

Beam type

SingleSplit

Pulse width (ms)

0.6

0.6

Ping rate (s)

1.4

0.2

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5 / 20PLOS ONECalibration of fisheries echo sounders using seabedFig 2. Shimaura Island, Miyazaki, Japan, where the research was conducted. The solid black line represents the survey line,
and the triangles indicate points where the sediment survey was conducted.
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6 / 20PLOS ONECalibration of fisheries echo sounders using seabedcalibration, the calibration ball was hung from 3 points on the vessel’s front, starboard, andport sides with fishing rods so that the calibration ball was directly under the transducer. To
confirm that the response from a general echo sounder is linear, the TS of the calibration ball
was measured at multiple depths ranging from 9m to 14m. Since the non-split-beam generalecho sounder could not measure the position of the target within the beam, the position of thecalibration ball was varied within the beam range to find the maximum TS (single observation). The beam width at a low frequency (15 kHz) is 32˚, and at a high frequency (200 kHz) is
6˚. The maximum TS of the calibration ball was checked using a dedicated tool manufactured
by Furuno, and the parameters such as depth, temperature, and salinity (when the maximum
TS was detected) were reflected in the recorded data manually. The calibration of the quantitative echo sounder was reflected using an automatic calibration mode [24], and the depth of thecalibration ball was roughly 11 m. Then, the Kakutomaru, equipped with the general andquantitative echo sounders traveled along the measurement line and simultaneously recorded
the measurements. The vessel speed was maintained at 3~5 knots when making acoustic measurements to prevent the entrainment of bubbles underneath the transducer [27]. Additionally, to compare the backscattering strength of the two echo sounders, the recording
conditions of both were standardized, with the pulse width being set as 0.6 ms and the depth
range being set as 40 m. Finally, we used a mud sampler (Ekman-Birge seabed sampler
5141-BW, RIGO Japan) along the measurement line [28], to examine the seabed sediments at
10 sites (Fig 2).

Analysis methods
The first step in the analysis procedure was to verify the accuracy of the general echo sounderthat was calibrated using the calibration ball. As a primary verification, the difference in thecalibration ball between the measured and theoretical TS was compared at each frequency. As
the general echo sounder was not a split beam, we used the maximum TS measured by the calibration ball [7]. In addition, general echo sounders will be used for stock estimation in the
future. Therefore, we conducted a secondary validation by comparing the fish abundance measured from the calibrated general and quantitative echo sounders. However, since the frequencies of the general and the quantitative echo sounders used in this study are different, it isdifficult to make a comparison using the backscattering strength of the fish school directly.
Therefore, we verified the accuracy by comparing the fish numbers calculated using Eq (7)from both echo sounders. After confirming the accuracy of the general echo sounder calibrated with a calibration ball, the data reflecting the calibration values were used to calculate
the standard values for the seabed. The standard values were then compared with the data that
did not reflect the calibration values to calibrate the echo sounder. Then, Reanalysis was performed using raw data corrected based on seabed backscattering strength. To verify the accuracy of the calibration carried out using the seabed backscattering strength, fish abundances
calculated from echosounders calibrated using a calibration ball and seabed were compared.
The acoustic data obtained from both echo sounders were analyzed using Echoview ver.
12.1 (Echoview Software Pty Ltd., Australian). Sa values were calculated based on the integration of volume backscatter as previously described to determine fish density [16,29]. Since
only fish schools were targeted in this analysis, Echoview’s fish school detection function wasused to extract the fish schools (Fig 3). The parameters for fish school extraction should bespecified based on the length or density of the target species [30]. During our survey period,
the target species was the Japanese anchovy (Engraulis japonicus), which was around 8.5 cm inbody length. Therefore, as parameters for the fish school detection function, the minimum
length and height for the candidate fish school were set as 3 m and 5 m was considered as the

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7 / 20PLOS ONECalibration of fisheries echo sounders using seabedFig 3. Echograms of the general (15 kHz) and quantitative (38 kHz) echo sounders. The area surrounded by black lines is the fish school of Japanese
anchovy detected by Echoview’s school detection function (minimum school length/height: 3 m, maximum vertical/horizontal linking distance in a single fish
school: 5 m).
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standard for the maximum vertical/horizontal linking distance in a single fish school. In addition, to eliminate the effects of noise from microorganisms (e.g. plankton and the suspended
sediments in the sea), the analysis threshold was set at -60 dB [31], and the areas of weak reflections below this threshold were not included in the analysis.
When the seabed was used in the analysis, determining the seabed line was essential to distinguish between echoes in the water column and seabed echoes. The integration volume
immediately below the seabed line was used to calculate the backscattering strength of the seabed. Since there are no scatters stronger than the seabed in the ocean, the depth of maximum
SV in each ping can be considered as the seabed [32]. In addition, since the TVG function is
not equipped with general echo sounders, scattered sound waves are immediately received
when the water depth is shallow, and saturation of the backscattering strength can be assumed.
Therefore, secondary reflections on the seabed were also considered in this study [33–35]. The
maximum echo from a candidate range of ±1 m from a water depth twice that of the seabed
was considered as the seabed secondary reflection [36,37]. However, as the recording range
was 40 m if the candidate range exceeded 40 m, we treated the record as an error and assumed
that secondary reflections of the seabed were not captured.
In the analysis of the seabed, Sv values were used as an acoustic indicator. In this study, theping rates differed depending on the echo sounder used; however, the distances traveled were

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the same because they were recorded at the same time. Therefore, the horizontal integration
range (hereinafter referred to as ‘grid’) when calculating the SVmean (average of the sv values
then converted back into the log measure) was based on the distance. According to previous
studies, the grid over which the average can be considered depends on the survey environment
and the echo sounder used [35,37–40]. In this study, the SVmean of the seabed primary and secondary reflections were extracted in 1, 5, 10, 50, 100, and 500 m grids. Additionally, the vertical
integration range for SVmean was 1 m below the seabed primary and secondary reflections for
all analyses. Then, the variability of SVmean extracted in each grid was compared using the chisquare test, with standard deviation and coefficient of variation as criteria. Data visualization
was then performed using the “ggplot” package of the statistical programming language R version 4.2.3 (R Core Team, 2023).
Finally, the seabed sediments collected at each site were classified using a simple grain size
analysis method, to determine their water content ratios and grain size compositions. The
water content ratio is the weight loss after air-drying the sample and is considered an essential
preliminary parameter of grain composition [41]. In this study, the grain size boundary of thegravel was 2 mm, the sand was 1/16 mm and less than 1/16 mm was mud [42]. Sediments
obtained from the survey were classified using the statistical software KyPlot [43].

Results and discussion I: Accuracy of general echo soundercalibrated using a calibration ball
Measured target strength (TS) of the calibration ballIn this study, the sound speed c was 1520.2 m/s, calculated from a water temperature of 21.4˚Cand a salinity of 30.4 psu. The maximum TS of the calibration ball was −41.3 dB at 15 kHz,measured at a depth of 11.3 m. Using the National Oceanic and Atmospheric Administration’s(NOAA’s) Standard Sphere Target Strength Calculator, the theoretical TS of the 15 kHz calibration ball calculated from the water temperature and salinity measured during the survey
was −41.3 dB [44,45]. Therefore, no difference between the measured and theoretical values.
At 200 kHz, the maximum value of the calibration ball was −38.8 dB, measured at a depth of
11.5 m. The theoretical TS of the 200 kHz was considered as −39.1 dB [7], and the difference
between the measured and theoretical values was as small as 0.3 dB.

Area backscattering strength (Samean) and estimated fish abundance
In the study area, we extracted the data for 45 fish schools as the Japanese anchovy groups. The
result of averaging the Sa of those 45 fish schools (Samean) was −22.5 dB at 15 kHz and −17.6
dB at 200 kHz for the general echo sounder, and −27.0 dB at 38 kHz and −30.0 dB at 120 kHz
for the quantitative echo sounder (Table 2). The TS of an 8.5 cm Japanese anchovy at 15 kHz
Table 2. Area backscattering strength (Samean, dB) for all fish schools obtained from each echo sounder and thenumber of Japanese anchovies (N) in the study area calculated using Samean and the TSs. TS is shown in previous
studies [46,47], and N here is the fish density n calculated in Eq 7 multiplied by the area of the fish school.
Samean (dB)

TS (dB)N

15 kHz (Cal. using calibration ball)

-22.5

-48.1

5,54,617

15 kHz (Cal. using seabed)

-22.1

-48.1

5,96,233

200 kHz (Cal. using calibration ball)

-17.6

-50.5

24,01,549

200 kHz (Cal. using seabed)

-17.0

-50.5

27,29,540

38 kHz

-27.0

-47.2

5,52,090

120 kHz

-30.0

-49.8

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9 / 20PLOS ONECalibration of fisheries echo sounders using seabedwas −48.1 dB, calculated using the regression equation for the general TS and body lengths[46]. The TS was −47.2 dB at 38 kHz, −49.8 dB at 120 kHz, and −50.5 dB at 200 kHz [47]. The
number of fish calculated using the Samean and TS for each frequency was 554,617 at 15 kHz
and 2,401,549 at 200 kHz. For the quantitative echo sounder, the number of fish was 552,090
at 38 kHz and 498,218 at 120 kHz. The number of fish estimated by the general echo sounder
showed a small difference from the quantitative echo sounder at low frequencies and a huge
difference at high frequencies.

Accuracy verification of calibrated general echo sounder
A comparison of the measured and theoretical TS of the calibration ball indicated that the difference between the measured and theoretical values was less than 0.3 dB at both frequencies
for the general echo sounder. In general, it is suggested that the difference between measured
and theoretical TS values should be within 1 dB [7]. Therefore, it is considered that a generalecho sounder, which is calibrated with parameters calculated from the maximum TS measurements of the calibration ball, could be used for acoustic measurements.
In terms of fish abundance for the entire study area estimated using Samean, the result of 15
kHz frequency for the general echo sounder was less different from the results of both frequencies for the quantitative echo sounder. In particular, the difference with 38 kHz was less than
1%. In general, in the case of the quantitative echo sounders, the frequency often used forresource assessment is 38 kHz, because low frequencies have a wider beam spread and stronger
backscattering strength from the fish school than high frequencies [6]. Since there was no significant difference in the overall number of fish at the low frequency of the two echo sounders,
we believe it will be possible to calculate the fish abundance using the low frequency of the calibrated general echo sounder. On the other hand, the results of 200 kHz for the general echosounder were highly overestimated. This is thought to be a result of the strong electrical transmission power [15]. The general echo sounder used in this study was used in the pelagic purse
seine fishery, and the transmission power for 200 kHz was set to 2kw to deliver sound waves todeeper depth zones. Instead, it is conceivable that at shallower depths, strong sound waves
would be reflected without enough attenuation. The use of too high a power level for the transmission of sound leads to a significant generation of sound at higher frequencies [48]. Therefore, resource estimation in shallow water using the high frequency of general echo sounders is
considered necessary to adjust electrical transmit power to the extent that it does not interferewith fishing operations.

Results and discussion II: Determination of seabed backscatteringstrength for calibration
Characteristics of volume backscattering strength (SV) of seabed extracted
from both echo sounders
For the seabed primary reflection, the number of pings extracted from the general echosounder was 4424. The SV at each ping is concentrated in the range of -16.2 dB to -15.7 dB at
15 kHz and -2.4 dB to -2.3 dB at 200 kHz, portraying no significant changes at both frequencies (Fig 4, Table 3). Unlike the results from the general echo sounder, the SV extracted fromthe quantitative echo sounder showed a change of about 20.0 dB at both frequencies. Additionally, the number of pings for the seabed secondary reflections extracted from the general echosounder was 1522, and the SV varied from −82.3 dB to −16.8 dB at 15 kHz and from −59.9 dB
to -25.5 dB at 200 kHz. Similar results were observed for the quantitative echo sounder, the SV

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PLOS ONECalibration of fisheries echo sounders using seabedFig 4. SV of seabed backscattering strength extracted at 1 ping from general and quantitative echo sounders plotted by ggplot. Above and below the solid
black lines are the maximum and minimum SV after excluding outliers. The top and bottom edges of the box show the upper quartile and lower quartile, andthe middle line shows the median. The white circles indicate mean SV.
https://doi.org/10.1371/journal.pone.0301689.g004

of seabed secondary reflections varied from −61.5 dB to −12.0 dB at 38 kHz and from -73.2 dB
to −23.2 dB at 120 kHz.
The backscattering strength of the seabed primary reflection obtained from the generalecho sounder showed a different trend from those obtained from the quantitative echosounder. Even though a 20 dB difference in SV was observed for the quantitative echo sounder,
more than 75% of the SV for the general echo sounder varied only within a range of 0.5 dB orTable 3. Volume backscattering strength (SV, dB) of single echoes extracted from primary and secondary seabed reflections at both echo sounders. SD stands forstandard deviation and CV for the coefficient of variation.
Primary reflection
Number of pings
General echo sounder
Quantitative echo sounder

15 kHz4424

Max.

Upper quartile

Lower quartile

Min.

Mean

SD

CV

-14.9

-15.7

-16.2

-16.8

-16.0

0.3

-2.0

200 kHz

4424

-1.9

-2.3

-2.4

-2.5

-2.3

0.1

-3.0

38 kHz

42568

-1.0

-2.5

-7.5

-18.0

-5.4

3.8

-69.9

120 kHz

42568

-1.0

-3.8

-10.8

-23.0

-7.7

4.8

-63.0

Lower quartile

Min.

Mean

SD

CV

Secondary reflection
Number of pings
General echo sounder
Quantitative echo sounderMax.

Upper quartile

15 kHz

1522

-16.8

-34.0

-45.6

-82.3

-40.3

9.4

-23.3

200 kHz

1522

-25.5

-40.5

-50.8

-59.9

-45.4

6.9

-15.2

38 kHz

13712

-12.0

-32.2

-42.0

-61.5

-37.2

7.0

-18.7

120 kHz

13712

-23.2

-39.6

-50.5

-73.2

-45.1

7.3

-16.2

https://doi.org/10.1371/journal.pone.0301689.t003

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PLOS ONECalibration of fisheries echo sounders using seabedless. Therefore, it is considered that most of the SV values of seabed primary reflection obtained
from the general echo sounders were saturated at both frequencies. In general, sound waves
attenuate with the transport distance in the ocean. However, if the water depth is shallow andreflected sound waves from the scatterers are too strong, the reflected sound waves may berecorded before being attenuated significantly [49]. Unlike quantitative echo sounders, theTVG function cannot be automatically executed as a function in the general echo sounder[50]. Because the TVG calculations were manually added to the recorded dataset, it is impossible to adjust the distance attenuation when recording the data, and the backscattering strengthof a strong scatterer like the seabed tends to saturate easily at shallow water depths.
On the other hand, it was observed that the SV of seabed secondary reflections obtained
from a general echo sounder varied with changes in the seabed. Since the secondary reflections
are reflections from the seabed ! water surface ! seabed, it is more affected by distanceattenuation than primary reflections and can more clearly represent changes in the seabed[37,51]. In addition, SV variations of more than 30 dB were observed at all frequencies of a general echo sounder. The reason can be considered that the echo attenuation is associated withvessel pitching and rolling, even assuming that the seabed is uniformly flat. Since slightchanges in vessel motion can lead to large variations in seabed echoes, it is considered necessary to use averaged SV values over some range when considering standard values for the seabed scattering strength. From the above, in this study, the standard value used for the seabedscattering strength was taken to be the secondary reflection (rather than primary reflection)
averaged over a certain range.

Seabed sediments and their volume backscattering strength (SV) of
secondary reflections extracted from general echo sounderThe seabed sediments of the 10 sites considered in this study were classified into 4 majorgroups (Fig 5). In all survey sites, the sediment properties portrayed a large proportion of
sandy sediments (35–97%). In particular, 5 sites (496, 498, 500, 502, 504; sandy) were dominated by sand (>90%). 3 sites (490, 492, 506; sandy-gravel) were dominated by sand, with
mixed gravel sediment, with the sand content being 68–76% and gravel content being 22–27%.
The remaining 2 sites (488; gravel-sandy, and 494; gravel) were dominated by gravel (>60%).
At these sites, no significant variation characteristics due to grain size composition wereobserved in the SV values of secondary reflections obtained from the calibrated general echosounder (Table 4). Certainly, differences in backscattering strength due to differences in seabed sediments are possible [52]. However, in some cases, there was a large overlap between the
distributions of the backscattering strength from sand and gravel [8,52]. Especially when theseabed sediment has not changed significantly, as in this study, it was difficult to characterize
the seabed backscattering strength. For these reasons, in this study, we used the backscatteringstrength of the seabed of all the surveyed areas, to determine the standard value to be used forthe seabed backscattering strength.

Volume backscattering strength (SVmean) of seabed secondary reflections
for each grid extracted from general echo sounder
At 15 kHz, the maximum value of SVmean did not change significantly with the grid (Fig 6,
Table 5). However, the variation between the maximum and minimum values of SVmean varied
from grid to grid. The SVmean calculated on a 1-m grid showed the greatest variation, approximately 46 dB. The 50-m grid was the boundary, which the SVmean tended to vary more for narrower grids than wider grids. Additionally, a similar trend was observed at 200 kHz, with the

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PLOS ONECalibration of fisheries echo sounders using seabedFig 5. Composition of seabed sediments classified using the KyPlot statistical software. The numbers portray the geographical positioning system (GPS)numbers for the 10 sites sampled. S denotes sand, G denotes gravel, and M denotes mud.
https://doi.org/10.1371/journal.pone.0301689.g005

50-m grid being the boundary. Variation of SVmean also varied with the grid; however, overall
was smaller than 15 kHz.
A possible reason for variation in SVmean for seabed secondary reflections is attenuation due
to surface bubbles generated by the pitching and rolling of the vessel [53]. In particular, thelower frequencies are more susceptible to bubbles, and this may be the reason why the SVmean
at 15 kHz is more varied than the SVmean at 200 kHz. In addition, the mean value of SVmean
becomes stronger as the grid becomes wider, and the variation is smaller from the 50-m grid.
It is suggested that even if there are changes in the seabed sediments, or even if there is vessel
pitching and rolling, these effects can be eliminated to some extent if the grid is wider than 50
m. However, setting the grid too wide means that changes in the seabed are largely ignored. To
eliminate this tradeoff as much as possible, SVmean values analyzed on a 50-m grid with a relatively wide grid were used as the standard values of the seabed secondary reflections for calibration (Fig 7).
Table 4. Grain size composition of the sediment and mean volume backscattering strength (SV) of the secondary reflections. SV is the value extracted by 1 ping fromthe general echo sounder.
GPS number

Gravel (%)

Sandy (%)

Mud (%)

Sediment

15 kHz200 kHz

488

62

35

3

Gravel sandy

30:7

39:7

490

24

68

8

Sandy gravel

30:2

33:6

492

22

76

2

Sandy gravel

28:0

39:5

494

95

3

3

Gravel

41:1

40:8

496

0

91

9

Sandy

-30.1

-36.6

498

0

97

3

Sandy

-29.5

-36.3

500

0

93

7

Sandy

-26.8

-41.6

502

1

90

9

Sandy

-39.1

-44.9

504

1

96

3

Sandy

-30.4

-34.1

506

27

72

1

Sandy gravel

20:4

27:4

https://doi.org/10.1371/journal.pone.0301689.t004

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PLOS ONECalibration of fisheries echo sounders using seabedFig 6. SVmean of seabed secondary reflections obtained from general echo sounder plotted by ggplot. The SVmeans were extracted in 1, 5, 10, 50, 100, and 500
m grids. Above and below the solid black lines are the maximum and minimum values after excluding outliers. The top and bottom edges of the box show theupper quartile and lower quartile, and the middle line shows the median. The white circles indicate average values.
https://doi.org/10.1371/journal.pone.0301689.g006

Results and discussion III: Demonstration of calibration method
using seabed secondary reflections
We calculated the backscattering strength of the seabed secondary reflections from generalecho sounder data that did not reflect the calibrated values of the calibration ball. The SVmean
extraction conditions were the same as for the SVmean used for the standard value. At 15 kHz,the SVmean had a maximum value of −14.5 dB, minimum value of −47.1 dB, and average valueof −28.5 dB; at 200 kHz, the SVmean had a maximum value of −65.2 dB, minimum value of−86.9 dB, and average value of −77.5 dB. Compared to the standard values of SVmean, there wasan average difference of 8.4 dB at 15 kHz and 34.1 dB at 200 kHz. This difference was used toTable 5. Maximum, minimum, and mean values of volume backscattering strength (SVmean, dB), which were calculated from each grid using the secondary seabedreflections obtained from the general echo sounder. SD stands for standard deviation and CV for the coefficient of variation.
15 kHz200 kHz

Grid

Max.

Min.

Mean

SD

CV

Max.

Min.

Mean

SD

CV

1m

-16.8

-63.0

-40.3

9.4

-23.3

-25.5

-59.9

-45.4

6.9

-15.2

5m

-19.4

-61.6

-39.9

9.0

-22.5

-25.5

-59.9

-45.3

6.8

-15.1

10m

-19.7

-58.9

-38.8

8.0

-20.5

-27.3

-58.6

-44.5

6.3

-14.3

50m

-23.1

-51.1

-36.9

6.3

-17.0

-31.1

-52.7

-43.4

5.9

-13.6

100m

-25.0

-55.5

-36.8

6.3

-17.0

-31.5

-52.1

-43.3

5.8

-13.4

500m

-26.6

-55.5

-37.0

6.7

-18.1

-31.5

-51.5

-43.1

5.8

-13.5

https://doi.org/10.1371/journal.pone.0301689.t005

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PLOS ONECalibration of fisheries echo sounders using seabedFig 7. Volume backscattering strength (SVmean) of seabed secondary reflections extracted on a 50m grid. The figures were interpolated using the general
kriging function of a spatial statistical method [ArcGIS 10.1, Environmental Systems Research Institute, Inc. (ESRI)].
https://doi.org/10.1371/journal.pone.0301689.g007

correct and reanalyze the data from the general echo sounder, which did not reflect the calibrated values.
Then, the accuracy of the calibration using the seabed backscattering strength was verified
by comparing the extracted Samean of the Japanese anchovy schools from the general echosounder calibrated with the seabed and with the calibration ball. The Samean extracted from thegeneral echo sounder calibrated by the seabed backscattering strength were −22.1 dB at 15
kHz and −17.0 dB at 200 kHz. At both frequencies, the differences in the Samean extracted fromthe general echo sounder calibrated by the seabed backscattering strength and those calibrated
by the calibration ball were less than 0.6 dB, which was very small (Table 2).
The results obtained from the general echo sounders calibrated using the seabed backscatteringstrength and the calibration ball did not differ significantly. Therefore, we could verify that the calibration method carried out using the seabed was effective. However, as discussed in the previous
section, the high-frequency transmission power used in this study was made stronger to search
for fish in deeper waters. Therefore, calibration performed by two methods may not correctly correct for backscattering strength, resulting in a strong reflection of shallow water and an overestimation of the resource. Additionally, since there was no significant difference in the Samean

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PLOS ONECalibration of fisheries echo sounders using seabedobtained from the low frequencies of the general echo sounder calibrated with the calibration balland seabed, we believe that the low frequency of the general echo sounder calibrated using the seabed backscattering strength can be used for stock assessment in the future.

Conclusions
In this study, we analyzed and verified the practicality of a new calibration method carried out
using the secondary reflection of the seabed obtained from a general echo sounder. In general,scientific echo sounder calibration using the seabed often uses the backscattering strength ofthe primary reflection [8–11,23]. However, general echo sounders are not equipped with a
TVG function, and the received signal from the primary reflection may be saturated in shallow
waters [49,54]. In future applications of general echo sounder calibration using the seabed, thelocation for setting the seabed standard values should be an area where fishing vessels pass by
daily without disturbing the fishermen. In this case, it will be chosen near fishing ports withshallow water depths, and it is difficult to avoid the saturation of primary seabed reflections.
Therefore, when using the seabed backscattering strength to calibrate general echo sounders inshallow areas, the use of secondary reflections is preferable to primary reflections. In addition,
if the angle between the seabed plane and the horizontal was not smaller than one-half of thebeam width, the secondary reflection of the seabed could not be accurately measured [35,55].
In this study, sand and gravel areas were selected where the seabed was not undulating. Nonetheless, the backscattering strength of seabed secondary reflections showed great variability.
Therefore, it can be assumed that there would be more variation in rocky areas with large
undulations on the seabed. In the future, when calibrating general echo sounders using seabedsecondary reflections in other areas, it is important to avoid rocky areas where the seabedchanges drastically and consider the areas that are as flat as possible.
There were large variations in the SV values of the seabed secondary reflections at all frequencies.
This variation was due to the complex effects of surface bubbles caused by the pitching and rollingof vessel motion and the decrease in echo level due to transducer surface motion. In particular, secondary reflections are more susceptible to these effects than primary reflections. In this study, theseeffects were reduced by averaging the echo level over a certain range. However, the relationshipbetween the vessel motion and the echo signal is still unclear and is a subject for future study. We
considered that the next step is to survey the variation in seabed backscattering strength due to vessel motions subjected to irregular external forces placed in the extremely random phenomenon ofocean waves. In addition, it has been reported that for the same general echo sounders, the measured backscattering strength varies by several dB with changes in seawater temperature [56].
Therefore, another future task in the seabed calibration of general echo sounders is to verify theeffect of changes in seawater temperature on the accuracy of the calibration.
In the future, applying the calibration method for general echo sounders using the seabedbackscattering strength, the general echo sounders installed on all fishing vessels can be modified to ‘quasi’ quantitative echo sounders. Stock assessment centered on fishing vessels can beestablished using inexpensive and widely used general echo sounders, instead of using expensive quantitative echo sounders. By using large datasets, we expect that there will be a smoothtransition in the fisheries industry, from adopting methods based on intuition and experienceto those based on scientific data.

Supporting information
S1 Table. Seabed volume backscattering strength (SV) extracted at a single ping was
obtained from the calibrated general echo sounder.
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PLOS ONECalibration of fisheries echo sounders using seabed

S2 Table. Area backscattering strength (Sa) values and the number of Japanese anchovies(n) obtained from each fish school.
(XLSX)

Acknowledgments
We thank all the members of the Laboratory of Marine Ecosystem Change Analysis for theirsupport in conducting this study.

Author Contributions
Conceptualization: Yanhui Zhu.
Formal analysis: Yanhui Zhu, Yoshihiro Nishiyama, Akinori Kasai.
Investigation: Yanhui Zhu, Minami Kenji, Tsutomu Tokeshi, Mitsuhiro Matsuura, Hikari
Horie.
Methodology: Yanhui Zhu, Minami Kenji, Tsutomu Tokeshi, Akinori Kasai, Mitsuhiro Matsuura, Hikari Horie.
Project administration: Kazushi Miyashita.
Software: Yoshihiro Nishiyama, Akinori Kasai.
Supervision: Kazushi Miyashita.
Validation: Yanhui Zhu.
Writing – original draft: Yanhui Zhu.
Writing – review & editing: Yanhui Zhu, Minami Kenji, Tsutomu Tokeshi, Yoshihiro
Nishiyama, Akinori Kasai, Mitsuhiro Matsuura, Hikari Horie, Kazushi Miyashita.

References
1.

Ichinokawa M, Nishijima S, Muko S, Kurota H, Ohshimo S. Alternative harvest control rules for achieving sustainable fisheries under the revised Fisheries Act in Japan: case studies in two Japanese sardine
stocks. Nippon Suisan Gakkaishi. 2022; 88(4): 239–255. https://doi.org/10.2331/suisan.21-00041

2.

Katsukawa T. Status of the ocean ecosystem and Japanese fisheries management. Environmental
information science. 2020; 49(1): 6–10.

3.

Tanaka K. Assessment and Management of Fisheries Resources in Japanese Territorial Waters and
EEZ—How do we weigh fish and catch them appropriately. Marine engineering: journal of the Japan
Institution of Marine Engineering. 2021; 56(2): 206–209. https://doi.org/10.5988/jime.56.206

4.

Amakasu K. Trends in Acoustic Survey Technology for Fishery Resources. Journal of the acousticalsociety of Japan. 2019; 75(1): 12–16. https://doi.org/10.20697/jasj.75.1_12

5.

Miyamoto Y, Uchida K, Amakasu K, Hasegawa K, Theparoonart Y, Anongponyoskun M, et al. Prototype of a simple acoustic survey system for attachment to a GPS plotter echo sounder. The journal of
the Marine Acoustics Society of Japan. 2016; 43(2): 71–78. https://doi.org/10.3135/jmasj.43.71

6.

Furusawa M. Quantitative Echo Sounder and Its Development. The Journal of the Acoustical Society ofJapan. 2019; 75(12): 669–676. https://doi.org/10.20697/jasj.75.12_669

7.

Furusawa M, Miyanohana Y, Sawada K, Takao Y. Calibration Manual for Quantitative Echo Sounders.
Technical report of National Research Institute of Fisheries Engineering (Fishing boat engineering).
1995; 15: 9–37.

8.

Weber TC, Ward LG. Observations of backscatter from sand and gravel seafloors between 170 and
250 kHz. Acoustical Society of America. 2015; 138(4): 2169–2180, https://doi.org/10.1121/1.4930185
PMID: 26520300

PLOS ONE | https://doi.org/10.1371/journal.pone.0301689 May 10, 2024

17 / 20

PLOS ONECalibration of fisheries echo sounders using seabed

9.

Eleftherakis D, Berger L, Le BN, Pacault A, Augustin JM, Lurton X. Backscatter calibration of high-frequency multibeam echosounder using a reference single-beam system, on natural seafloor. Marine
Geophysical Research. 2018; 39: 55–73. https://doi.org/10.1007/s11001-018-9348-5

10.

Roche M, Degrendele K, Vrignaud C, Loyer S, Bas TL, Augustin JM, Lurton X. Control of the repeatability of high frequency multibeam echosounder backscatter by using natural reference areas. Marine
Geophysical Research. 2018; 3: 89–104. https://doi.org/10.1007/s11001-018-9343-x

11.

Hjellvik V, Robertis AD. Vessel Comparison on the Seabed Echo: Influence of Vessel Attitude. NOAA
Technical Memorandum. 2007; NMFS-AFSC-171.

12.

Furusawa M. Consideration on TVG of Echo-sounder. Technical report of National Research Instituteof Fisheries Engineering (Fishing boat and instrument). 1985; 6: 33–49.

13.

Yamatani K. About the Latest Echo Sounder Systems. The Society of Naval Architects of Japan. 1990;
730: 208–214. https://doi.org/10.14856/zogakusi.730.0_208

14.

Furusawa M. Designing quantitative echo sounders. The Journal of the Acoustical Society of America.
1991; 90(26): 26–36. https://doi.org/10.1121/1.401297

15.

Lunde P, Pedersen AO, Korneliussen RJ, Tichy FE, Nes H. Power-budget and echo-integrator equations for fish abundance estimation. Fisken og Havet. 2013; no. 10/2013.

16.

Abe K. Mechanism of Acoustic Fisheries Resource Survey: Estimation of Existing Resources by EchoIntegral Method (<Feature> Survey Mechanisms). Kanrin: bulletin of the Japan Society of Naval Architects and Ocean Engineers. 2020; 33: 31–36. https://doi.org/10.14856/kanrin.33.0_31

17.

Furusawa M, Sawada K. Effects of Transducer Motion on Quantifying Single Fish Echoes. Nippon Suisan Gakkaishi. 1991; 57(5): 857–864. https://doi.org/10.1121/1.401297

18.

Yang L, Chen Y., Zhang J. Calibration of echosounder using standard target method. MATEC Web ofConferences. 2019; 283: 1–4. https://doi.org/10.1051/matecconf/201928305005

19.

Imazeki A, Mine Y, Takasu Y, Hamada E. Calibration of Transmitting and Receiving System of EchoSounder by used Ballbearing. Bulletin of the Japanese Society of Fisheries Oceanography. 1992; 56(2): 121–130.

20.

Traynor JJ, Ehrenberg JE. Fish and standard-sphere target-strength measurements obtained with adual-beam and split-beam echo-sounding system. Rapp. R-v. Réun. Cons. int. Explor. Mer. 1990; 189:
325–335.

21.

Saneyoshi J, Nakamura K. Theory and Model Experiment on Reflection of Ultrasonic Waves from
Numerous Reflectors. The Journal of the Acoustical Society of Japan. 1952; 8(3): 123–127. https://doi.
org/10.20697/jasj.8.3_123

22.

MacLennan DN. Acoustical measurement of fish abundance. The Journal of the Acoustical Society ofAmerica. 1990; 87, 1–15. https://doi.org/10.1121/1.399285

23.

Aoyama C, Hamada E, Furusawa M. Total Performance Check of Quantitative Echo Sounders byUsing Echoes from Sea Bottom. Nippon Suisan Gakkaishi. 1999; 65(1): 78–85. https://doi.org/10.
2331/suisan.65.78

24.

Tang Y, Furusawa M. Minimization of interference by sea surface and bottom reverberations in measuring surface fish abundance by scanning sonar. Nippon Suisan Gakkaishi. 2003; 69(2): 153–161.
https://doi.org/10.2331/suisan.69.153

25.

Miyanohana Y. Ultrasonic Methods for Locating and Weighing Fish Stocks. Research journal of foodand agriculture. 1994; 17(12): 22–26.

26.

Wong H, Chesterman WD. Bottom Backscattering near Grazing Incidence in Shallow Water. The Journal of the Acoustical Society of America. 1968; 44: 1713–1718. https://doi.org/10.1121/1.1911318

27.

Simmonds J, MacLennan D. Fisheries Acoustics-Theory and Practice Second Edition. Massachusetts:
Blackwell Publishing; 2006.

28.

Hinokio R, Ishida M, Yamazaki H. Effect of Substance Concentrations in Sediments using Various
Types of Sediment Samplers: A study on surface sediments contamination by the Fukushima Daiichi
Nuclear Power Station Accident. Environmental conservation engineering. 2015; 44(8): 452–459.
https://doi.org/10.5956/jriet.44.452

29.

MacLennan DN, Fernandes GP, Dalen J. A consistent approach to definitions and symbols in fisheries
acoustics. ICES Journal of Marine Science. 2002; 59: 365–369. https://doi.org/10.1006/jmsc.2001.
1158

30.

Coetzee J. Use of a shoal analysis and patch estimation system (SHAPES) to characterise sardine
schools. Aquatic Living Resources. 2000; 13(1): 1–10. https://doi.org/10.1016/S0990-7440(00)00139X

31.

Kang M. Current technology of fisheries acoustics based on analyzed acoustic data using Sonar Data’s
Echoview. ACOUSTICS. 2006; 493–497.

PLOS ONE | https://doi.org/10.1371/journal.pone.0301689 May 10, 2024

18 / 20

PLOS ONECalibration of fisheries echo sounders using seabed

32.

Tanoue H, Komatsu T, Hamano A. Determination of upper boundary of an acoustic blind zone producedby the rugged bottom during a survey using a quantitative echosounder. Bulletin of the Japanese Society of Fisheries Oceanography. 2013; 77(2): 53–58.

33.

Patterson RB. Using the Ocean Surface as a Reflector for a Self-Reciprocity Calibration of a Transducer. The Journal of the Acoustical Society of America. 1967; 42: 653–655.

34.

Aoyama C, Hamada E, Furusawa M, Saito K. Calibration of Quantitative Echo Sounders by Using Echofrom Water Tank Surface. Nippon Suisan Gakkaishi. 1997; 63(4): 570–577. https://doi.org/10.2331/
suisan.63.570

35.

Anderson JT. Acoustic seabed classification of marine physical and biological landscapes. ICES cooperative research report. No. 286; 2007.

36.

Burns DR, Queen CB, Sisk H, Mullarkey W, Chivers RC. Rapid and convenient acoustic sea-bed discrimination for fisheries applications. Proceedings of the Institute of Acoustics. 1989; 11(3): 169–178.

37.

Hamilton LJ. Acoustic Seabed Classification Systems. DSTO-TN-0401. 2001.

38.

Ellingsen KE, Gray JS, Bjornbim E. Acoustic classification of seabed habitats using the QTC VIEW system. ICES Journal of Marine Science. 2002; 59(4): 825–835. https://doi.org/10.1006/jmsc.2002.1198

39.

Siwabessy PJ, Tseng Y, Gavrilov AN. Seabed habitat mapping in coastal waters using a normal incident acoustic technique. Proceedings of ACOUSTICS 2004. 2004; 187–192.

40.

Wada M, Hatanaka K, Toda M. A study of making a bathymetric chart by fish finder for fisheries. IPSJSIG Technical Report. 2007; 2007-UBI-14: 63–67.

41.

Narita H. Marine Observation Guidelines (Sediment Analysis). The Oceanographic Society Japan.
2017; 5: 1–6.

42.

Wentworth CK. A Scale of Grade and Class Terms for Clastic Sediments. The journal of Geology.
1922; 30(5): 377–392.

43.

Yokoyama H, Ishihi Y. Zoning of the inner part of Ariake Sound based on principal component analysisof sediment factors. Nippon Suisan Gakkaishi. 2009; 75(4): 674–683. https://doi.org/10.2331/suisan.
75.67444.

MacLennan DN. The theory of solid spheres as sonar calibration targets. Scottish Fisheries Research.
Report Number 22. 1981.

45.

MacLennan DN, Dunn JR. Estimation of sound velocities from resonance measurements on tungsten
carbide calibration spheres. Journal of Sound and Vibration. 1984; 97(2): 321–331. https://doi.org/10.
1016/0022-460X(84)90325–0

46.

McCartney BS, Stubbs AR. Measurements of the acoustic target strengths of fish in dorsal aspect,
including swimbladder resonance. Journal of Sound and Vibration. 1971; 15(3): 405–420. https://doi.
org/10.1016/0022-460X(71)90433-0

47.

Kang D, Cho S, Lee C, Myoung J, Na J. Ex situ target-strength measurements of Japanese anchovy(Engraulis japonicus) in the coastal Northwest Pacific. ICES Journal of Marine Science. 2009; 66:
1219–1224. https://doi.org/10.1093/icesjms/fsp042

48.

Korneliussen RJ, Diner N, Ona E, Berger L, Fernandes PG. Proposals for the collection of multifrequency acoustic data. ICES Journal of Marine Science. 2008; 65: 982–994. https://doi.org/10.1093/
icesjms/fsn052

49.

Fujii M, Nogi Y. Acoustic mapping of the seafloor features: Implication for global environmental change.
Low temperature science. 2018; 76: 269–284. https://doi.org/10.14943/lowtemsci.76.269

50.

Aoyama C, Matsumoto R. Acoustic Surveys of Methane Plumes by Quantitative Echo Sounder inJapan Sea and the Estimate of the Seeping Amount of the Methane Hydrate Bubbles. Journal of Geography. 2009; 118(1): 156–174. https://doi.org/10.5026/jgeography.118.156

51.

Jackson DR. APL-UW high-frequency ocean environmental acoustic models handbook. Applied Physics Laboratory, University of Washington, Technical Report. 1994; 9407(102): IV21-IV36.

52.

Tao L, Motooka S. Improvement of the Discrimination by Introducing the Reflection Properties of Different Seabed Materials. Steering committee of symposium on ultrasonic electronics. 2005; 26: 37–38.
https://doi.org/10.24492/use.26.0_37

53.

Hamano A, Sanetoh S, Mizutani S, Sumikawa Y, Uchida K. Effects of ship motion and survey conditions
on volume backscattering strength in acoustic survey. Nippon Suisan Gakkaishi. 1988; 54(9): 1533–
1543. https://doi.org/10.2331/Suisan.54.1533

54.

Yokoyama K, Umeda M, Yamazaki H. Development of acoustic techniques for suspended sedimentconcentration measurement. Annual journal of hydraulic engineering. 2005; 49: 547–552. https://doi.
org/10.2208/prohe.49.547

PLOS ONE | https://doi.org/10.1371/journal.pone.0301689 May 10, 2024

19 / 20

PLOS ONECalibration of fisheries echo sounders using seabed

55.

Voulgaris G, Collins M. USP RoxAnn ground discrimination system: a preliminary evaluation. Admiralty
Research Establishment, Portland, UK. University of Southampton, Department of Oceanography,
Marine Consultancy Services, Technical Report No: SUDO/TEC/90/5C. 1990.

56.

Demer DA, Renfree JS. Variations in echosounder–transducer performance with water temperature.
ICES Journal of Marine Science. 2008; 65: 1021–1035. https://doi.org/10.1093/icesjms/fsn066

PLOS ONE | https://doi.org/10.1371/journal.pone.0301689 May 10, 2024

20 / 20