Vol. 55, 2016

(update: 2016.8.3)

Batch-like Arrival Waves of Glass Eels of Anguilla japonica in Offshore Waters of Taiwan

Yu-San Han^1,*, Chau-Ron Wu², and Yoshiyuki Iizuka³

¹Institute of Fisheries Science and Department of Life Science, College of Life Science, National Taiwan University, Taipei 10617, Taiwan
²Department of Earth Sciences, National Taiwan Normal University, Taipei 11677, Taiwan. E-mail: cwu@ntnu.edu.tw
³Institute of Earth Sciences, Academia Sinica, Nangang, Taipei 11574, Taiwan. E-mail: yiizuka@earth.sinica.edu.tw

(Received 1 May 2015; Accepted 25 May 2016)

Yu-San Han, Chau-Ron Wu, and Yoshiyuki Iizuka (2016) The larval stage of Anguilla japonica includes a long dispersal time over a long distance. In theory, the larvae should be distributed evenly throughout their transportation route when using both the NEC and Kuroshio, but the hypothesized new moon spawning of mature eels should lead to recruited glass eels exhibiting batch-like arrival waves, with a one-month-long cycle. However, environmental disturbances could mask the expected batch-like waves of glass eel recruitment. Thus, this phenomenon is best observed in glass eels collected from offshore waters, which are closer to the spawning site and less disturbed by these environmental factors. The offshore area of Yilan, Taiwan, is a suitable place to observe the arrival dynamics of the A. japonica glass eel. In this area, batch-like waves of glass eel arrival of A. japonica were observed, with peaks occurring between the last quarter and first quarter lunar periods, with a near one-month periodicity. No arrival peaks were found during the full moon period, suggesting that the glass eels exhibit light-avoidance behavior. Furthermore, all of the batches of arrivals were in the early pigmentation stage and similar in age (around 150-160 days), suggesting that they are likely a new arrival cohort. The tracer simulation showed that the mean tracer drift time, from the presumed spawning site to Yilan, was 155 ± 19.8 days. The observed batch-like arrival waves of glass eels in the offshore waters of Taiwan support the “New Moon Hypothesis,” which suggests that there is synchronized spawning behavior of the eels during the new moon period.
Key words: North Equatorial Current, Kuroshio, Larval duration, Arrival wave.

*Correspondence: Tel: +886-2-33663726. Fax: +886-2-33669449. E-mail: yshan@ntu.edu.tw