Fig 1.
The imagery of general echo sounder evolution.
Traditional general echo sounders could only capture fish signals. However, current general echo sounders can calculate backscattering strength by adding the TVG function to those fish signals. R is the range, SV is the volume backscattering strength for multiple targets, and TS is the target strength for a single target.
Table 1.
Settings for the general and quantitative echo sounders used in this study.
Fig 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.
Fig 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).
Table 2.
Area backscattering strength (Samean, dB) for all fish schools obtained from each echo sounder and the number 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.
Fig 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, and the middle line shows the median. The white circles indicate mean SV.
Table 3.
Volume backscattering strength (SV, dB) of single echoes extracted from primary and secondary seabed reflections at both echo sounders.
SD stands for standard deviation and CV for the coefficient of variation.
Fig 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.
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 from the general echo sounder.
Fig 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 the upper quartile and lower quartile, and the middle line shows the median. The white circles indicate average values.
Table 5.
Maximum, minimum, and mean values of volume backscattering strength (SVmean, dB), which were calculated from each grid using the secondary seabed reflections obtained from the general echo sounder.
SD stands for standard deviation and CV for the coefficient of variation.
Fig 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)].