碩士 / 國立臺灣海洋大學 / 環境生物與漁業科學學系 / 96 / Like other marine ecosystem in the world, coastal waters of Taiwan are under pressures of human’s fishing activities and environment ental change. The change of food pyramid structure has been undergoing, however, the rate and status are unknown. In this study, we used Fisheries Yearbook data and landing data from Fishery Administration’s database to calculate Mean Trophic Level (MTL), Contribute Trophic Level (CTL), and Fishing-in-Balance (FiB), in order to analyze the effect that the coastal fisheries have on the coastal waters ecosystem in Taiwan. To understand the long-term shift of seasonality of migratory species, we used ratio-to-moving-average method to calculate Season Index (SI), and examine seasonality by ANOVA, then we analyzed the composite seasonality changes hidden in the landing data. The results of this study are as following:
1) The MTL in Taiwan coastal waters increased during 1963~1993, then went down after 1993 at a rate of 0.015/yr. However, the catch still increased at the same time, and low TL species became the target. Meanwhile, both MTL in the eatern and western waters were in decreasing trend with rates of 0.008/yr and 0.02/yr, respectively.
2) After examining the coastal species with high CTL during 1963~2005, the catch rate of long-lived species mainly consist of large pelagic fish and demersal fish decreased yearly. One the other hand, the catch rate of short-lived species consist mainly of small pelagic fish and small demersal fish increased yearly. High CTL species in the eastern waters are all large migratory fish with TL>4. In the western waters, high CTL species are mainly small pelagic fishes and demersal fishes.
3) The FiB in the coastal waters increased yearly and the value “0.7” peaked in 1993, which implied the fisheries had more utilization on high trophic level. Then the FiB went down and kept at the value of 0.5, which meant the over catch of high trophic level decreased. The trends of FiB in the east and west are in opposite ways. The FiB for the eastern waters decreased and the average decreasing rate was 0.03/yr. On the contrary, FiB for the western waters increased year after year and the average increasing rate was 0.04/yr.
4) In recent decades, those species peaked in spring increased, but those species peaked in winter decreased gradually. After 1990s, those species peaked in summer increased year after year. For those species with bi-peak mode, the catch rate of species with peaked in summer and autumn went down from 1960s, and reached the lowest point in 1980s, then increased after 1990s. However, catch rate of species with peaks in spring and winter were in opposit way, which imply that there were more summer migratory species.
The trends of MTL and FiB values indicated that the resource utilization of Taiwan coastal fishery were unbalanced. The large fishes at high trophic level decreased gradually, but small pelagic fishes increased at the same time. The phenomenon of “fishing down the marine food webs” were very significant after 1993. The average MTL decreasing rate were higher than world’s average speed in continental shelves. In addition, the variation of catch for species with single peak suggested that peak-in-spring, and peak-in-summer species gradually predominate over peak-in-winter species year after year. Therefore, in addition to the catch pressure, the climate changes may result in the catch variation of small pelagic fishes. As the inter-annual fluctuations of small pelagic fishes were much higher than others, the structure of food pyramid for the coastal fisheries were weaken even more, which need to pay more attention on.
| Identifer | oai:union.ndltd.org:TW/096NTOU5451019 |
| Date | January 2008 |
| Creators | He-Jia Sin, 何珈欣 |
| Contributors | Hsueh-Jung Lu, 呂學榮 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 103 |
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