## 3 Results  
The surface water temperature and salinity of the surveyed area were 22.08 to 22.87 \({}^{\circ}\)C (mean 22.48 \({}^{\circ}\)C) and 32.74 to 33.72 psu (mean 33.23 psu) in October 2020, and 28.30 \({}^{\circ}\)C and 27.4 psu in July 2021, respectively. The mean water depths for hauls 01, 02, and 03 of the mid-water trawl were 104.2, 107.6, and 110.3 m, respectively (Table 1). During the survey period, a total of 22 species were caught through three mid-water trawls, among which 19 species were identified from 12,625 stereo images obtained using Deep Vision, thus indicating that 86% of the fish species caught in the trawl were identified by Deep Vision (Table 2). The remaining three species that were not photographed were the Japanese jack mackerel, Pacific rudderfish (_Psenopsis anomala_), and yearnose genadier (_Caelorinchus multispinulosus_) in haul01. In terms of populations, a total of 2102 individuals were collected through trawling, among which a total of 1083 (52%) were identified using Deep Vision. The deviation of the populations between the two survey methods ranged from 0% to 2000%, with the largest difference of 2000% being obtained for ch  
Figure 4: Example of tracking fish through sequential images 1 to 3. The white arrow indicates the movement of each species. for skinnycheek lanternfish (_Bentlosema pterotum_) in haul01, whereas Japanese flying squid (_Todarodes pacificus_), john dory (_Zeus fuber_), Pacific rudderfish, and slender ribbonfish (_Trachipterus islikawae_) in haul03 showed no difference in populations. A comparison of the length measurements of 589 individuals caught by mid-water trawl with the lengths of 433 individuals measured using Deep Vision image revealed statistically significant differences with respect to largehead hairtail (\(t=-3.04\), \(p=0.0228\)) and glowbelly (_Acropoma japonicum_) (\(t=-2.67\), \(p=0.0111\)) in haul01 and Japanese jack mackerel (\(t=4.65\), \(p=0.0000\)) in haul03. There were, however, no significant difference in length measurements obtained for other species (Table 3). \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Haul01**} & \multicolumn{2}{c}{**Haul02**} & \multicolumn{2}{c}{**Haul03**} \\ \cline{2-7}
**Species** & **N** & **W** & **N** & **W** & **N** & **W** \\ \hline Chub mackerel (_Somber japonicus_) & 143 & 28.9 & 6 & 1.1 & & \\ Glowbelly (_Acropoma japonicum_) & 292 & 0.5 & 310 & 0.4 & & \\ Indian perch (_Jaydia linetata_) & 1233 & 2.2 & & & & \\ Japanese flying squid (_Todarodes pacificus_) & & & & 7 & 2.5 \\ Japanese jack mackerel (_Trachurus japonicus_) & 29 & 2.7 & 24 & 3.4 & 1149 & 253.0 \\ John dory (_Zeus faber_) & & & & 4 & 1.5 \\ Largehead hairtail (_Trichurus lepturus_) & 1952 & 158.7 & 6 & 0.7 & 186 & 10.6 \\ Pacific rudderfish (_Psenopsis anomalous_) & 29 & 2.7 & 7 & 0.7 & 4 & 0.1 \\ Sharptobou seabass (_Synagroys philipinensis_) & & & 98 & 0.2 & & \\ Silver pomfret (_Pamps arrest_) & 200 & 19.5 & & & & \\ Skinnycheek lanternfish (_Bentlosema pterotum_) & 4239 & 4.0 & & & & \\ Sender ribbonfish (_Trachipterus islikawae_) & & & & 4 & - \\ Spearmanose grenadier (_Caolarinchus multispinulos_) & 21 & 0.2 & & & \\ Yellow croaker (_Larimichtus polyactis_) & 2102 & 39.5 & & & & \\ \hline Total & 10,240 & 258.9 & 451 & 6.5 & 1354 & 267.7 \\ Number of species & 10 & 6 & & 6 & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Species composition of fish collected using a mid-water trawl in the Western Sea off Jeju Island. N and W are number of individuals per unit area (ind./km\({}^{3}\)) and wet weight per unit area (kg/km\({}^{3}\)), respectively.