博士 / 國立海洋大學 / 漁業科學學系 / 90 / The impact of bottom trawlers on demersal environment has been awarded worldwide. The shrimp beam trawlers in southwestern Taiwan have used electric stimulate to increase the catch for more than 40 years. However, its impacts on these waters have never been evaluated. The objectives of this study are to estimate the catch composition and fishing efficiency and its impact on marine environment. Also it tries to find out the optimal electric power of stimulation and optimal mesh size of cod end. The results derived in this study can be used as a reference for sustainable utilization and fishery management of this fishery. The results are as follows:
1. Spatial and temporal variation of catch composition
There are 142, 105, and 118 species identified from the catches of shrimp beam trawlers in the three major fishing bases namely, Chiayi, Hsingta, and Tongkang, respectively. Only 10 species can be found year round in all three areas. Catch was categorized as landing and discard. Landed shrimps are the major catch no matter in weight or number in the first areas, while bycatch is major catch in Tongkang. Location was found to be the key factor determining the catch composition and structure based on diversity index and cluster analysis.
2. Comparison of fishing efficiency of gears with and without electric stimulate
Comparing the fishing efficiency of gears with and without electric stimulate and, day and night, it is found that the fishing efficiency with electric stimulate is the best for catch landed shrimps in the day time with a 4.75 stimulate efficiency.
3. The impact of electric stimulate on demersal animals
Shrimp size is increasing with increasing electric power of stimulate and no lethal dead was found with normal trawling speed and electric stimulate. The goal of stimulating shrimps can also be achieved by reducing the electric power of 50%. No significant improvement of survival rate of hatching was found for Metapenaeus ensis with electric stimulate. Based on the laboratory experiment, the residuals of Copper Chloride and Cuprous Chloride resulted from electric stimulate have no significant effect on the survival of fishes and shrimps.
4. Survival rate of discards and mesh selectivity
The mean survival rates of discarded shrimp, crab, cephalopods, and fish are estimated to be 56.3%, 62%, 34.8%, and 8.4%, respectively. The landings and discards of dominant shrimp species decrease as the mesh size increases. For example, the landing decreased 6%, 21%, and 47%, and discards decreased 28%, 55%, and 69% for the most common species, Parapenaeopsis cornuta as the mesh size increased from 23.5 mm to 28, 32.5, and 37 mm, respectively. An optimal mesh size was suggested to be 28～32.5 mm based on the consideration of fisherman’s income and discards reduction.
| Identifer | oai:union.ndltd.org:TW/090NTOU0451027 |
| Date | January 2002 |
| Creators | Chao-Ching Chen, 陳朝清 |
| Contributors | Yau-Shou Chow, 周耀烋 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 157 |
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