Spatiotemporal variation of mature and immature bigeye tuna(Thunnus obesus) related to oceanographic and climatic indices in the Pacific Ocean

• Main Authors: Lin, Tzu-Hsiang, 林子翔
• Other Authors: Lan, Kuo-Wei
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/wp2a78

碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 107 === The bigeye tuna (Thunnus obesus, BET) is one of the important commercial species for longline fisheries in Pacific Ocean. In this study, we collected the records of bigeye tuna catch rates, length data of longline fisheries and divided into immature and mature cohorts. We also collected the satellite-base oceanographic data of sea surface temperature (SST)、sea surface height (SSH)、sea surface salinity (SSS)、mixed layer depth (MLD) and chlorophyll-a concentration (CHL) and three climate indices including Oceanic Nino Index (ONI)、Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO). The generalized additive models (GAMs) were used to investigate the relationships between environmental variables and catch rates for evaluating the fishing condition of the immature and mature cohorts of BET. The results showed the spatial distribution of the immature cohorts were concentrated in the central and northern Pacific Ocean, and the mature cohorts were shifted followed seasonal environment variations in the central Pacific Ocean. The GAMs model selection processes showed the cumulative deviances explained by selected GAMs were 35.4% and 56.4% for immature and mature cohorts, respectively. The results showed the catch rates of immature and mature cohorts had similar pattern and were significantly correlated with environmental variables of SST in the range 26-28℃, 0.1-0.2mg/m3 of CHL, 34.5-35.5 psu of SSS, 0.4-0.5 m of SSH, and 50-100 m of MLD. However, it is a similar result for immature and mature cohorts, the SST and MLD explained the highest deviance for both cohorts, but the SSH explained the third deviance for the immature cohorts, and CHL was revealed for the mature cohorts. The BET shows that the catch rates were increased due to the movement of the warm water mass in Pacific Ocean when the ONI was in positive events. In addition, in the negative PDO events, the abundance of BET food organism (zooplankton and ichthyoplankton) had decreased trends and influenced the lower recruitment of immature cohorts and catch rates of mature cohorts after 2-3 years.