The study aims at developing the selective fishing gear which can catch only shrimp. Because the shrimp beam trawl fishery has been conducted in the coastal waters of South Korea, and its mesh size of the cod end is extremely small which may cause overfishing juveniles of fisheries resources. Moreov...
The study aims at developing the selective fishing gear which can catch only shrimp. Because the shrimp beam trawl fishery has been conducted in the coastal waters of South Korea, and its mesh size of the cod end is extremely small which may cause overfishing juveniles of fisheries resources. Moreover a concern of destroying the ecosystem occurs because of the small mesh size of the shrimp beam trawl.
To reach the goal of the study, first of all, the field trawl survey using a prototype net were conducted in the shrimp fishing grounds such as Boryeong and Buan of the West Sea, Kangjin, Tongyeong and Geoje of the South Sea to investigate the species composition and body length distributions of shrimp species and bycatch from 30 April to 13 November 2005.
To choose the selective fishing gear to be applicable in the circumstances of South Korea, a general type gear, a double-level type gear, and a grid type gear were selected from model experiments and field surveys. In especial, the dimensions of a grid were 800W × 1,200L (mm), it was attached 45° in front of the cod end. The interval of grid bar(φ 10 mm) was 50 mm.
The model experiments were performed to test opening efficiency and towing tension. The experimental tanks were the flume tank〔8.0 L × 2.8 W × 1.4 H (m)〕and the towing tank〔85 L ×10 W × 3.5 H (m)〕in National Fisheries Research and Development Institute.
Three type of the model net were prepared based on the Tauti's Similarity Law of Fishing Gear in 1/4, 1/2 scale considering the dimensions of the experimental tanks.
Moreover, the aims of this study were to raise the selectivity of shrimp catch while developing the grid type gear to be performed better than the general type, and to attempt the automation of a trawl which fits the Korean shrimp beam trawl fishery from March 2006 to April 2010.
The results of this study were as follows;
The number of shrimp species from the shrimp beam trawl was 10. Of ten species, palaemon gravieri was occupied 50% of the total shrimp catch and Crangon Hakodatei was occupied 46%. The remaining species were Trachysalambria curvirostris, Parapenaeopsis tenellus, Rhynchocinetes uritai, Matapenaeus joyneri, Solenocera melantho, Fenneropenaeus chinensis, Alpheus digitalis, Marsupenaeus japonicus in order.
Bycatches consisted of 30 fish species, 6 mollusk species, 5 shellfish species and 3 crab species, and their catch weight were 47.0%, 16.6%, 13.6%, 5.5% and 2.7% respectively.
The bycatch rate by the number of fish caught was occupied 37.5% of the total number, and that by weight caught was 59% of the total weight.
The vertical opening was constantly lower as towing velocity increased. The relationship between the vertical opening(H) and the towing velocity(V) at the general type gear, the double-level type gear, and the grid type gear were
H(Ge) = 0.43 - 0.22․V (R2 = 0.9377)
H(D) = 0.45 - 0.16․V (R2 = 0.9756)
H(Gr) = 0.40 - 0.17․V (R2 = 0.9000)
The towing tension increased as the towing velocity became high. The relationship between the towing tension(T) and the towing velocity(V) at the general type gear, the double-level type gear, and the grid type gear were
T(Ge) = 3.26․V0.96 (R2 = 0.9682)
T(D) = 1.67․V1.63 (R2 = 0.9532)
T(Gr) = 1.71․V2.05 (R2 = 0.9972)
Results from the field surveys using the double-level type gear, the selectivity was low. Meanwhile, when the grid type gear was compared with the general type gear, it showed 12% of bycatch rate by the number of fish caught and 3% of bycatch rate by weight caught lower than those from the general type gear. hence, the grid type gear was chosen for a selective fishing gear in this study.
To improve the catch ability of the grid type gear, the netting comprised of 100knots of a width was added to the side panel of the general type gear, and the width of the cod end became constantly from the front to the rear. As a consequence, the shrimp catch per swept area (m2) from the grid type gear was 0.23(the number of fish) compared to 0.05 from the general type gear. The bycatch rates by the number of fish caught and weight caught using the grid type gear were 4.2% and 42.6%, respectively, which were lower 2.4% and 7.6% than those using the general type gear.
The selectivity in regard with the fish body shape was not good in fusiform and anguilliform fish as well as mollusk, and it was good for compressed form and depressed form fish, and crustacea. When the angle of attck of grid was lowered 30°, it was distinctively decreased garbage to be piled in front of the grid.
To adapt the automatic catching system, a hauling gear(1,350L × 700W mm) was installed right behind the bridge to control hydraulic pressure. As a result it was convenient when casting and hauling the trawl warp.
The catchability of the grid type gear with the window net was the same as the general type gear, namely 0.02(the number of fish) per swept area(m2) was shown in both gears.
However, the bycatch rates by the number of fish caught and weight caught were 32.2% and 85.9%, respectively, which lowed 16.4% and 8.3% compared to those in the general type gear. The selectivity in regard to the fish shape affected all fish shapes, in particular 61% of selectivity was confirmed in fusiform fish and 33% of that was in compressed form fish.
The grid type gear with the window net had 35mm of the interval of the grid bar. Using this gear, the bycatch rates by the number of fish caught and weight caught showed 10.5% and 33.1%, respectively, which meant that they were 6.2% and 33.9% lower than those in the general type gear.
Therefore, the grid type gear with the window net was consequently decided as the most suitable selective fishing gear in the shrimp beam trawl fishery in South Korea.
The study aims at developing the selective fishing gear which can catch only shrimp. Because the shrimp beam trawl fishery has been conducted in the coastal waters of South Korea, and its mesh size of the cod end is extremely small which may cause overfishing juveniles of fisheries resources. Moreover a concern of destroying the ecosystem occurs because of the small mesh size of the shrimp beam trawl.
To reach the goal of the study, first of all, the field trawl survey using a prototype net were conducted in the shrimp fishing grounds such as Boryeong and Buan of the West Sea, Kangjin, Tongyeong and Geoje of the South Sea to investigate the species composition and body length distributions of shrimp species and bycatch from 30 April to 13 November 2005.
To choose the selective fishing gear to be applicable in the circumstances of South Korea, a general type gear, a double-level type gear, and a grid type gear were selected from model experiments and field surveys. In especial, the dimensions of a grid were 800W × 1,200L (mm), it was attached 45° in front of the cod end. The interval of grid bar(φ 10 mm) was 50 mm.
The model experiments were performed to test opening efficiency and towing tension. The experimental tanks were the flume tank〔8.0 L × 2.8 W × 1.4 H (m)〕and the towing tank〔85 L ×10 W × 3.5 H (m)〕in National Fisheries Research and Development Institute.
Three type of the model net were prepared based on the Tauti's Similarity Law of Fishing Gear in 1/4, 1/2 scale considering the dimensions of the experimental tanks.
Moreover, the aims of this study were to raise the selectivity of shrimp catch while developing the grid type gear to be performed better than the general type, and to attempt the automation of a trawl which fits the Korean shrimp beam trawl fishery from March 2006 to April 2010.
The results of this study were as follows;
The number of shrimp species from the shrimp beam trawl was 10. Of ten species, palaemon gravieri was occupied 50% of the total shrimp catch and Crangon Hakodatei was occupied 46%. The remaining species were Trachysalambria curvirostris, Parapenaeopsis tenellus, Rhynchocinetes uritai, Matapenaeus joyneri, Solenocera melantho, Fenneropenaeus chinensis, Alpheus digitalis, Marsupenaeus japonicus in order.
Bycatches consisted of 30 fish species, 6 mollusk species, 5 shellfish species and 3 crab species, and their catch weight were 47.0%, 16.6%, 13.6%, 5.5% and 2.7% respectively.
The bycatch rate by the number of fish caught was occupied 37.5% of the total number, and that by weight caught was 59% of the total weight.
The vertical opening was constantly lower as towing velocity increased. The relationship between the vertical opening(H) and the towing velocity(V) at the general type gear, the double-level type gear, and the grid type gear were
H(Ge) = 0.43 - 0.22․V (R2 = 0.9377)
H(D) = 0.45 - 0.16․V (R2 = 0.9756)
H(Gr) = 0.40 - 0.17․V (R2 = 0.9000)
The towing tension increased as the towing velocity became high. The relationship between the towing tension(T) and the towing velocity(V) at the general type gear, the double-level type gear, and the grid type gear were
T(Ge) = 3.26․V0.96 (R2 = 0.9682)
T(D) = 1.67․V1.63 (R2 = 0.9532)
T(Gr) = 1.71․V2.05 (R2 = 0.9972)
Results from the field surveys using the double-level type gear, the selectivity was low. Meanwhile, when the grid type gear was compared with the general type gear, it showed 12% of bycatch rate by the number of fish caught and 3% of bycatch rate by weight caught lower than those from the general type gear. hence, the grid type gear was chosen for a selective fishing gear in this study.
To improve the catch ability of the grid type gear, the netting comprised of 100knots of a width was added to the side panel of the general type gear, and the width of the cod end became constantly from the front to the rear. As a consequence, the shrimp catch per swept area (m2) from the grid type gear was 0.23(the number of fish) compared to 0.05 from the general type gear. The bycatch rates by the number of fish caught and weight caught using the grid type gear were 4.2% and 42.6%, respectively, which were lower 2.4% and 7.6% than those using the general type gear.
The selectivity in regard with the fish body shape was not good in fusiform and anguilliform fish as well as mollusk, and it was good for compressed form and depressed form fish, and crustacea. When the angle of attck of grid was lowered 30°, it was distinctively decreased garbage to be piled in front of the grid.
To adapt the automatic catching system, a hauling gear(1,350L × 700W mm) was installed right behind the bridge to control hydraulic pressure. As a result it was convenient when casting and hauling the trawl warp.
The catchability of the grid type gear with the window net was the same as the general type gear, namely 0.02(the number of fish) per swept area(m2) was shown in both gears.
However, the bycatch rates by the number of fish caught and weight caught were 32.2% and 85.9%, respectively, which lowed 16.4% and 8.3% compared to those in the general type gear. The selectivity in regard to the fish shape affected all fish shapes, in particular 61% of selectivity was confirmed in fusiform fish and 33% of that was in compressed form fish.
The grid type gear with the window net had 35mm of the interval of the grid bar. Using this gear, the bycatch rates by the number of fish caught and weight caught showed 10.5% and 33.1%, respectively, which meant that they were 6.2% and 33.9% lower than those in the general type gear.
Therefore, the grid type gear with the window net was consequently decided as the most suitable selective fishing gear in the shrimp beam trawl fishery in South Korea.
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