Variability of total length of Japanese glass eels in relation to the environmental factors during migration route

• Main Authors: Chi Ma, 馬霽
• Other Authors: Yu-San Han
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/bxvf42

碩士 === 國立臺灣大學 === 漁業科學研究所 === 107 === Japanese eel (Anguilla japonica) is an important commercial freshwater fish in East Asia. However, eel aquaculture is a typical capture‐based aquaculture. Recruitment of Japanese eel has declined since 1980s, and large interannual fluctuations were also observed. The causes of decline or extremely poor recruitment events remain unclear. By using numerical modelling method to reproduce larval migration routes, previous studies showed that the inter-annual variability of ocean circulation may influence the migration success of Japanese eel. However, the effect of environmental factor on wild larvae is less discussed by biological points of view. In this study, a recent 8–yr total length data of Japanese glass eel was used as representative of eel larval condition to evaluate the effect of environment by generalized additive model. And the environment experienced by eel larvae was based on a coupled biological physical model which were the used to estimate the migration routes. The result of generalized additive model showed larger total length of Japanese glass eel were observed at 21-24.5°C for spawning area temperature, higher than 24°C for migration routes temperature, 0.03-0.07 mg/m3 for spawning area chlorophyll concentration, higher than 13 mg/m3 for accumulated migration routes chlorophyll concentration with increasing trend, 35.1-35.3 psu for spawning area salinity, and during El Niño year. The environment of spawning area has greater effect on glass eel total length. The results correspond to previous studies in laboratory experiment, except the effect of spawning area temperature. The synchronized spawning behavior in Japanese eel may cause the density-dependent effect which potentially influence the result of this study. This study provided a different perspective of environmental effect on Japanese larvae, and may help to understand the cause of recruitment fluctuation.