碩士 / 國立臺灣大學 / 漁業科學研究所 / 91 / Gillnet fishery is one of the most important fisheries in the coastal and offshore waters of Taiwan. The fishermen usually catch the specific size fishes of target species by some gillnets and/or trammel nets with various mesh sized. The purpose of this study is to investigate the species and size selectivity of gillnets and trammel nets with various mesh sizes in the area. The comparing experiments between gears were undertaken in the fishing harbors of Zhu-Wei, Tao-Yuan County and Gen-Fan, I-Lan County by the chartered fishing vessels from 2000 to 2002. In addition, many catches of gillnet vessels in the two fishing harbors were also measured. The mesh sizes 2.7, 3.8, 4.0, 4.5, 5.3, and 6.0 Taiwanese inch (1 Taiwanese inch = 3.03cm) of gillnets as well as 2.7, 3.4, 3.8, 4.5, and 5.5 inch of trammel nets were adopted in the fishing harbor of Zhu-Wei, Tao-Yuan County. The gillnet with mesh size 3.0 inch and the trammel net with 2.8 inch were also adopted in the fishing harbor of Gen-Fan, I-Lan County. The comparisons of species selectivity between gears were undertaken by the similarity coefficient, cluster analysis, and diversity index. The size selectivity curves of dominant species were estimated by the Sechin method (inference from girth measurements) for the measuring variables of fork length, eye girth, head girth, and maximum body girth. The results were as follows.
The low similarity coefficients between gears indicated that the species selectivity was dispersed between gears. The catch composition of gillnet with 2.7 inch size was the most special among all gears. The high diversity indices of most gears indicated that the specific target species of gillnet fisheries were not clear. The caught body positions were between head girth and maximum girth for those enmeshed fishes. The theoretical size selectivity curves estimated by the Sechin method after modifying the variables of mesh sizes were fitted well to the observed data for the most dominant species.
| Identifer | oai:union.ndltd.org:TW/091NTU00451005 |
| Date | January 2003 |
| Creators | LIU, KUO-CHIANG, 劉國強 |
| Contributors | 李英周 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 0 |
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