Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan.
Sci Rep. 2019 Feb 4;9(1):1384. doi: 10.1038/s41598-018-37569-5.
Extraordinarily poor recruitment of Japanese eels in East Asia has been generally reported during extreme El Niño years. However, the scenario failed to take place during the 2015-16 extreme event. In this study, we examined possible factors responsible for differing eel abundance in East Asia during the two strongest recent extreme El Niños, which occurred in 1997-98 and 2015-16. Numerical tracer experiments were carried out to determine why the impacts on eel catches seen in 1997-98 were not repeated in 2015-16. Among physical factors, two scenarios are likely responsible for extremely poor recruitment in East Asia: southward migration of the North Equatorial Current (NEC) or southward movement of eel spawning grounds. Comparing the latitudinal shift of NEC locations between the 1997-98 and 2015-16 El Niños, we conclude that NEC migration may be a factor, but is not chiefly responsible, for lower eel catches. Our findings pointed to southward movement of spawning grounds as the dominant factor. The northward movement of spawning grounds during 2015-16 meant that eel larvae were preferentially transported into the NEC-Kuroshio system, which resulted in a higher rate of recruitment success. The distinct evolution and dynamics of these two El Niño events led to different spawning ground locations, impacting eel abundance in East Asian countries.
东亚地区的日本鳗鱼捕捞量异常减少的情况在极端厄尔尼诺年已普遍报道。然而，这种情况并未在 2015-16 年的极端事件中发生。在这项研究中，我们研究了东亚地区在最近两次最强的极端厄尔尼诺事件（1997-98 年和 2015-16 年）期间，鳗鱼丰度不同的可能原因。我们进行了数值示踪剂实验，以确定为什么 1997-98 年的鳗鱼捕捞量受到影响的情况在 2015-16 年没有重演。在物理因素中，有两种情况可能导致东亚地区鳗鱼的繁殖量极低：北赤道流（NEC）的向南迁移或鳗鱼产卵场的向南移动。通过比较 1997-98 年和 2015-16 年厄尔尼诺期间 NEC 位置的纬度偏移，我们得出结论，NEC 迁移可能是一个因素，但不是造成鳗鱼捕捞量较低的主要原因。我们的研究结果表明，产卵场的向南移动是主要因素。在 2015-16 年期间，产卵场向北移动意味着鳗鱼幼鱼更优先地被输送到 NEC-黑潮系统，这导致了更高的繁殖成功率。这两次厄尔尼诺事件的不同演变和动态导致了不同的产卵场位置，从而影响了东亚国家的鳗鱼数量。
