| Summary: | 碩士 === 國立高雄海洋科技大學 === 漁業生產與管理研究所 === 95 === In order to reduce the bycatch rate in sergestid shrimp midwater trawl, and avoid negative influence on fishery resources caused by higher bycatch rate, it was necessary to modify the design of fishing gear for achieving the goal of management on fisheries resources. The panel/grid and open door in upper front of codend which linked obliquely toward upside from its bottom to top were conducted into this study. It changed different obliquely angle to analysis of separative efficiency and escaping rate of bycatch species. A total of fifteen trips was carried out by commercial fishing boat in Kaoping Canyon during July, 2005 to May, 2007. The results are as follows：
1. Comparison of square mesh and different frame structure for separative efficiency：
a. The grids has more separative efficiency than square mesh.
b. The circle frame with square mesh and with horizontal lines reached obliquely at 80°, main fishing target, Sergia lucens on second inner layer was 60~70% and upper codend was 10~20% respectively. When grids reached obliquely with 60°and 40°, the catch of target species was reducing on second inner layer while it was increasing on upper codend.
c. For Non-target larger fish such as Trichiurus lepturus at the same protocol, its catch rate of upper codend was 70~80%. For Other non-target fish such as Benthosema pterotum, it was increasing on upper codend.
2. Considering the Difficulty of Selective Index, the design of circle frame with square mesh and horizontal lines with 80°had the loweret values and were 0.81 and 0.80, respectively.
This result suggested when grid change obliquely at 80°, the catch of main fishing target, Sergia lucens losses lesser and segregation of non-target fish and shrimp is better.
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