Comparison of standardized abundance index of bigeye tuna (Thunnus obesus) in the Atlantic Ocean by three general linear models

• Main Authors: Jen-Ting Lo, 羅壬廷
• Other Authors: Chien-Chung Hsu
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/81836853958975596054

碩士 === 國立臺灣大學 === 海洋研究所 === 95 === The bigeye tuna （Thunnus obesus） is worldwide in tropical and subtropical waters of the Atlantic, Indian and Pacific oceans. It is distributed from 50 degree north to 45 degree south in Atlantic oceans, and Taiwanese fishery catch bigeye tunas which used longline in its tropical waters. The volume of catch rose to 8,500 t. in 1970, followed by a slow decline for 20 years. In 1991, the volume soared to 13,850 t., and reached the peak in 1996 (21,850 t.). After 1998, the volume is close to the restriction on an annual catch of 16,500 t. Though limited, the overall catches volume is still rising constantly. It is estimated that the resource of this species is going to dwindle by year. To effectively evaluate the resource status, the research has adopted important indicators, such as standardized catch per unit effort and other biomass index. However, fishing effort is easily affected by human and environmental factors. So the research will attempt to standardize fishing effort before adopting any resource assessment data. Thus, the research adopts three general types of statistic program: General linear model, General linear mixed model and General additive model, followed by utilizing several information criterions which were widely used as a criterion of model selection in fish population dynamics to determine the optimal method to standardize. The results of three different models have shown the same pattern, starting from 1982, the population of Atlantic bigeye tuna is gradually decreasing by year. The level was high during 1992 to 1996, and dropped to bottom in 1998. The level rose till 2002, then dropped again. If as presumed, the species is at the lowest level among all years. However, under heavy fishing effort and high catches, time series catch per unit effort by Taiwanese longline fishery still shows mismatch in standardized catch per unit effort. The indicator should be reevaluated.