## 3 Results  
### Vertical Distribution by Species  
Using the dB-differences, the vertical distribution of _Gadus macrocephalus_ is shown in the figure below, and the depth of the survey area was found to be in the range from 50 m to 250 m or more. The horizontal axis represents the time, the number at the top indicates the number of the survey line according to the movement of the survey line, the vertical axis represents the depth of water, and the thin solid line represents the water depth at 50 m intervals. The color scale on the right shows the intensity of sound waves received after they were reflected by the fish school. The higher the fish School, the darker brown that represents it.  
At line 1, acoustic scattering layers in the range of \(-61\) to \(-64\) dB were distributed at the sea bottom with a depth of 50 m, and at line 2, acoustic scattering layers in the range of \(-52\) to \(-64\) dB were distributed at the sea bottom with a depth of 150 m. At line 3, with 100 m depth, acoustic scattering layers in the range of \(-52\) to \(-64\) dB were distributed, and at lines 4 and 5, acoustic scattering layers in the range of \(-56\) to \(-67\) dB were distributed. At lines 6 and 7, acoustic scatterers in the range of \(-61\) to \(-70\) dB were distributed at the sea bottom with a depth of 150 m. At lines 9 and 10 with 50 and 120 m depths, acoustic scattering layers in the ranges of \(-37\) and \(-52\) to \(-70\) dB were distributed (Figure 7).  
Figure 5: Common squid identification example.  
Figure 6: Herring identification example.  
As a result of examining the distribution of _Engraulis japonicus_ using the dB-difference, lines 1 and 2 did not show the echogram of _Engraulis japonicus_, and at lines 3 and 4, acoustic scattering layers in the ranges of \(-46\) to \(-64\) dB and \(-52\) to \(-64\) dB were distributed at 100 m depth. At line 5, acoustic scattering layers in the range of \(-64\) to \(-70\) dB were distributed at 100 m depth, and at lines 6 and 7, acoustic scatterers in the range of \(-64\) to \(-70\) dB were distributed. At lines 9 and 10 with 50 and 100 m depths, acoustic scatterers in the ranges of \(-43\) and \(-61\) to \(-70\) dB were distributed (Figure 8).  
As a result of examining the distribution of _Todarodes pacificus_ using the dB-difference, at line 1, acoustic scatterers in the range of \(-61\) to \(-67\) dB were distributed at a depth of 50 m, and at lines 2 and 4, acoustic scatterers in the range of \(-64\) to \(-67\) dB were distributed at a depth of 50-100 m. At line 5, acoustic scatterers in the range of \(-37\) to \(-55\) dB were distributed at 80 m depth, and at lines 6 and 7, acoustic scatterers in the range of \(-61\) to \(-70\) dB were distributed (Figure 9).  
Figure 8: Vertical distribution of pacific cod.  
Figure 7: Vertical distribution of pacific cod.  
As a result of examining the distribution of _Clupea pallasii_ using the dB-difference, at line 1, acoustic scattering layers at \(-46\) and \(-61\) dB were distributed at a depth of 50 m, and at lines 2 and 4, acoustic scatterers in the ranges of \(-37\) to \(-46\) dB and \(-52\) to \(-64\) dB were distributed at a depth of 50-100 m. At line 5 with 90 m depth, acoustic scattering layers in the range of \(-37\) to \(-46\) dB were distributed, and at lines 6 and 7, acoustic scattering layers in the range of \(-52\) to \(-64\) dB were distributed at a depth of 150 m. At line 8, acoustic scattering layers in the range of \(-37\) to \(-46\) dB were distributed at a depth of 50 m. At line 9, with 10 and 70 m depths, acoustic scattering layers in the ranges of \(-34\) to \(-40\) dB and \(-40\) to \(-46\) dB were distributed (Figure 10).  
As a result of examining the vertical distribution of each fish species, _Gadus macrocephalus_ was mostly detected at the sea bottom, and _Engraulis japonicus_ and _Todarodes pacificus_ were mainly detected at a depth of 50 m. _Clupea pallasii_ was mostly detected at a depth between 50 and 150 m.