Spatial and temporal variability in length of Japanese glass eel, Anguilla japonica
Date Issued
2012
Date
2012
Author(s)
Ho, Min
Abstract
The Japanese eel Anguilla japonica is an important aquaculture species in Northeast Asia countries, however, all of the eel fry needed for aquaculture depends on the wild catch. That the Japanese eel stock has declined rapidly in recent decades has resulted in the decreasing glass eel catch and the eel aquaculture industry is facing serious problems. Therefore, understanding the recruitment dynamics of the Japanese eel can propose references for the utilization, preservation and management of the glass eels. The aim of this study is to investigate the spatial and temporal variation of the total length (TL) of the estuarine Japanese glass eels. This study uses a total of 19,059 Japanese glass eel specimens which had been collected from Taiwan, mainland China, North Korea and Japan for 28 years since 1983. After measuring TL and observing pigmentation stages, the results revealed that mean TL of the glass eels decreases gradually from the stage VA to stage VIA2, but from stage VIA3, there is an abruptly increase. Although both the monthly and annual mean TL varies considerably, the long term trend is not significant. The fluctuation of mean TL oscillation seems has some relationship with El Niño and La Niña events. In general, the TL of Japanese glass eel during El Niño period is above the regression line. Besides, the TL of Japanese glass eel during the La Niña period is below the regression line. In other words, the mean TL of Japanese glass eel in La Niña year was shorter than the other years; this may be due to the shorter larval duration. The spatial analysis of TL of Japanese glass eel reveals that the TL of most Japanese glass eels increases with latitude and this phenomenon may have some relationship with longer larval duration for northern glass eels. In conclusion, the resource of Japanese eel has been decreasing significantly for past 30 years and suffered from global warming. However, there is no significant impact on the TL trend of Japanese glass eels. The ENSO events and the transportation velocity will influence the larval duration, thus influence the size of the estuarine glass eels.
Subjects
Japanese eel
Anguilla japonica
glass eel
pigment stage
total length
El Ni?o
La Ni?a
latitude
SDGs
Type
thesis
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