博士 / 國立臺灣大學 / 海洋研究所 / 89 / The South Atlantic albacore resource was utilized mainly by Taiwanese and Brazilian longliners and the baitboats from South Africa and Namibia. The annual South Atlantic albacore production ranged from 25,000 to 40,000 mt in last decade, and more than 60% was caught by Taiwanese longliners. The main purpose of this study was to evaluate the stock status of South Atlantic albacore and to provide better scientific criteria needed for management purpose.
The objectives of this study are: (1) to estimate of the growth equation of South Atlantic albacore by MULTIFAN method; (2) to elucidate the geographical distribution of South Atlantic albacore based on Taiwanese longline fisheries; (3) to standardize CPUE of South Atlantic albacore using GLM methods; and (4) to assess of the stock status by using ASPM model. The results obtained are as follows:.
The von Bertalanffy growth parameters, based on the length frequency data sets from 1965 to 1969 by MULTIFAN, were: 0.213 year-1, 119.2 cm and -0.392 year for K, L∞ and t0, respectively. Comparison on growth curve of South Atlantic albacore obtained in this study and that of Lee and Yeh (1993) showed no significant difference was observed between the two curves when size of fish in the range from 70 cm to 110 cm.
Two main fishing patterns can be identified in Taiwanese longline fisheries, i.e., regular longline fishery (RLL) and deep longline fishery (DLL). RLL was characterized by having less than or equal to 9 branch lines deployed between floats, whereas DLL had 12 or more branch lines. The operating waters were also distinctive for RLL and DLL. RLL mainly operated southward of 15∘S; on the other hand, DLL operated northward of 10∘S.
A total of three ecological subareas in the South Atlantic Ocean can be identified, based on clustering results of the catch rates among 12 fish or fish species. Subarea 1 covered the waters northward of 10∘S~15∘S; Subareas 2 and 3 were consecutively located southward of 10∘S~15∘S. The differences in albacore’s catch rate among subareas were significant. RLL was mainly operated in Subareas 2 and 3 targeting albacore; while bigeye tuna was the target species for DLL in Subarea 1. As the boundary of Subarea 2 expanded northwards, the marginal rate of area regrouping (MRAR) showed a systematic declining tendency. Moreover, the coefficient of determination (R2) from the GLM procedure in CPUE standardization of South Atlantic albacore became smaller when Subarea 2 incorporated some parts of Subarea 1. Both results suggest that the demarcation of the boundary between Subareas 1 and 2 is appropriate.
Standardized CPUE trends, obtained either from GLM or GENMOD procedures, were quite similar. The abundance index of South Atlantic albacore showed a decreasing trend until the historic low level in 1990. However, since the beginning of the 1990s, the stock appeared to recover. The level of abundance in 1995 was almost equivalent to that of 1984.
The results of the ASPM and sensitivity tests suggest that under the present fishing intensity, the South Atlantic albacore resource is still in healthy condition.
| Identifer | oai:union.ndltd.org:TW/089NTU00279042 |
| Date | January 2001 |
| Creators | C. L. Wu, 吳繼倫 |
| Contributors | S. Y. Yeh, 葉顯椏 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 149 |
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