The annual production of silver croaker (Argyrosomus argentatus) in Korean towed fishing gears has been increased in recent five years. In 2017, the annual production of silver croaker in metric ton was increased 99.2% compared to 2013. However, the research for silver croaker has been focused on ecology in Korea. There has not been enough research in terms of fishing gears. Therefore, the research for retention probability for towed gears was conducted on covered codend method from June, 2016 to July, 2018. During the experiments, the total catch of silver croaker was 1,563. The geometry of the experimental trawl gear was controlled by trawl monitoring system; net height was 3.3 m, distance of trawldoors was 59.8 m and distance of wing net was 17.3 m. The selection curve for silver croaker was estimated by a logit model. The analysis was applied with the confidence interval to reduce uncertainty of the estimation. The l50 was 13.87 cm and its selection range was 2.71 cm. P-value was estimated at 0.99. The mesh size for silver croaker in towed gears needs to be adjusted by considering its minimum maturity length, stakeholder’s interests and fisheries regulations.

Most grid sorting has been used to sort out flatfish in shrimp fisheries, while double grid systems have been tested to separate smaller shrimp. The escape of juvenile red seabream through separating panels made with steel grids or large mesh tested for masking effects in a two-species system. Fish behavior was observed in a circulating water tank. The escape rate was 20% greater with the separating codends than with the normal codend in the single-species experiments. The rates in the two-species experiments were 30% or 20% greater than the single-species rates for the normal or separating codends, respectively. The seabream retention rates in the grid separator codend decreased as rockfish retention increased, possibly due to a threat effect. Conversely, the retention rate of both species increased concurrently in the net separator, possibly due to a masking effect. The escape rates of juvenile red seabream varied by compartment in the mesh separating codend. These results suggest that grid separating codends can be used in the field as towed fishing gear to reduce juvenile catch.

Experimental fishing was carried out to compare the catches of main species and bycatch according to the codend mesh size (raschel, 15mm, 25mm, 35mm, 45mm) of stow net on anchor in the coastal waters of Seocheon after manufacturing five kinds of fishing gears and commercial fishing boat (7.93 tons) was used for it. Anchovy (Engraulis japonicus), southern rough shrimp (Trachysalambria curvirostris), beka squid (Loligo beka), cuttle fish (Sepia esculenta), swimming crab (Portunus trituberculatus) were dominant on the five kinds of experimental fishing gears. Southern rough shrimp was caught from all kinds of fishing gears and catches of anchovy was highest in the raschel codend, southern rough shrimp for 15mm, 25mm, 35mm codend and beka squid for 45mm codend. Bycatch proportion against total catches was 623,376g (28.7%) for 2,171,844g in raschel, 11,932g (1.7%) for 704,451g in 15mm, 3,616g (1.6%) for 221,432g in 25mm, 9,276g (4.9%) for 191,052g in 35mm and 2,724g (5.3%) for 51,431g in 45mm.

Experimental fishing was carried out to compare fishing status according to the codend mesh size (raschel, 15mm, 25mm, 35mm, 45mm) of stow net on anchor in the coastal waters of Seocheon after manufacturing five kinds of fishing gears and commercial fishing boat (7.93 tons) was used for it. Total catches of raschel, 15mm, 25mm, 35mm, 45mm codend were 816,949g, 203,994g, 1,405g, 51,576g, 194g in September and 40,545g, 66,974g, 14,692g, 12,647g, 12,655g in October. Dominance species were anchovy (Engraulis japonicus) in raschel codend, largehead hairtail (Trichiurus lepturus) in 15mm and 35mm in September, and the amount of catches was very small in 25mm and 45mm codend due to the fishing gear damage. In October, dominance species were anchovy and beka squid (Loligo beka) in raschel, 15mm, 25mm codend, and cuttlefish (Sepia esculenta) and beka squid were mainly caught in 35mm and 45mm codend. In addition, total length of anchovy and cardinal fish (Apogon lineatus) were increased according to the increase of codend mesh size but there was no difference in the mantle length of cuttlefish and loligo beka.