| 英文摘要 |
Blockage of water at midstream of the Yangtze River for the construction of the Three Gorges Dam in recent years might have been the cause to the substantial reduction of nutrient being carried to the East Sea, and affect the production and fishery resources of Taiwan’s north sea. This study analyzes the differences in catch resources of the northern sea region before and after the first river blockage of June 2003 on the Yangtze. Statistical data of chlorophyll concentration from satellite images as well as CPUE value, species composition in the area, and torch-light fishery and mackerel purse seine fishery spatio-temporal fluctuations were examined. Data from satellite images indicate that prior to the river blockage, chlorophyll concentration on the East Sea shelf began to increase in June, and reached a peak of 0.76mg/m3 by April the following year. In May, this concentration began to plunge, and hit bottom by June (0.25mg/m3). After river blockage to the Yangtze at midstream began, changes in concentration pattern remained the same, but the amount of concentration changed significantly. With the exception to May and June, the remaining months saw an average drop in chlorophyll concentration level of 16.4%. Furthermore, data from fishery resources indicate that, prior to the river blockage, the CPUE value of squid for March from torchlight fishery was 31kg/net, and increased to 118kg/net. Between May and September, such value fluctuated between 66 to 97kg/net, and increased again in October to 138kg/net. By November, this plummeted to 40kg/net. After river blockage to the Yangtze, the CPUE value of quid fluctuated between 29 to 58kg/net from March to November, showing no significant differences in catch amount year round. Comparison of CPUE values before and after the blockage show that CPUE value for squid dropped an average of 50% each month after river blockage (March data excluded). However, data of catch composition from mackerel purse seine fishery show that while warm water mackerel increased significantly, cold water horse mackerel was gradually decreasing. Torch-light fishery and mackerel purse seine fishery are two major coastal fisheries of Taiwan, it is believed that changes in resources and species composition in the fishing area are the result of reduced fresh water being flushed to the East Sea from the river blockage, causing a drop in basic reproduction and changes in currents (stronger warm Kuroshio Current and weaker cold coastal current), and subsequently reduction in squids but increase of warm water fish. |
