Fluctuation in spawning behavior and larval transport of the Japanese eel associated with global oceanic change

日本鳗鲡的产卵地位于太平洋的北赤道海流（NEC）。然而，关于鳗鱼及其幼虫在NEC下游分布的几个未解之谜仍然存在，而且不太可能仅凭观察就能解决。其中三个问题是：1)之前对产卵地的错误判断；2)在台湾西海岸捕获大量幼虫，而不是在东海岸；3)韩国沿海水域的幼虫丰度低。在这项研究中，我们通过数值模拟证明了这些问题的答案可以用北太平洋的水循环来解释。与ENSO（厄尔尼诺和南方涛动）相关的盐度锋的运动控制了从NEC产卵地到东亚苗圃的大量幼虫运输。在过去的30年里，盐度锋从13°N移动到17°N。由于15°N以北的幼虫运输条件较差，这种盐度锋向北移动可能可以解释20世纪70年代以来日本玻璃鳗捕鱼量的年代际线性减少。本文还提出了以NAO（北大西洋涛动）指数为特征的年代际尺度海洋气候变化来解释美洲和欧洲鳗鲡玻璃鳗捕捞量下降的原因。1975年南方涛动指数和NAO指数同时进入另一个阶段，与大的变化有关，在20世纪70年代中期开始了太平洋和大西洋玻璃鳗捕捞量的下降。这种对应关系表明，全球海洋气候变化通过相似的物理过程影响了太平洋和大西洋遗传亲缘物种的迁徙行为，并最终控制了它们的鱼类资源。

Spawning ground of the Japanese eel is located in the North Equatorial Current (NEC) in the Pacific Ocean. However, several unanswered questions about the distribution of the eel and their larvae downstream of the NEC remain and are unlikely to be resolved by the observations alone. Three such questions are about 1) previous mis-determination of spawning ground, 2) large larval catch off the west coast of Taiwan, not off the east coast, 3) low abundance of larvae in Korean coastal waters. In this research, we have demonstrated that answers to these questions can be explained by the water circulation in the North Pacific by using numerical simulations. Movement of the salinity front associated with ENSO (El Nino and Southern Oscillation) controls abundance of larval transport from the spawning ground in the NEC to the nursery ground in the East Asia. The salinityfront has moved from 13°N to 17°N during last three decades. Since condition of larval transport north of 15°N is worse, this northward displacement of the salinity front probably can explain decadal scale linear decreasing of the Japanese glass eel catch from the 1970s. In this research, decadal scale ocean-climate change charecterized by the NAO (North Atrantic Oscillation) index was also proposed to explain decline of glass eel catch of the American and European eels. Associated with large regime shift in 1975, the Southern Oscillation Index and NAO index changed to another phase simultaneously and the decline of the glass eel catch in both the Pacific and Atlantic oceans was started in the mid 1970s. This correspondence suggests that the global ocean-climate changes afect migration behavior of the genetically close-related species in the Pacific and Atlantic Oceans through similar physical processes, and finally control their fish stocks.