Study on the mechanisms behind species replacement between sardine and anchovy populations in the Enshu-nada Sea

20世纪70年代，随着恩舒那达海日本沙丁鱼种群的迅速增长，日本鱼种群，特别是春季产卵鱼种群开始下降。在沙丁鱼的主要产卵期（2 - 3月），捕食性浮游生物和竞争性中上层鱼类（如鱼）的缺乏显然有利于沙丁鱼的补充成功。在1980年代后期，沙丁鱼开始衰落，被沙丁鱼取代。值得注意的是，在这一阶段，沙丁鱼的产卵期推迟了几个月，其背后的一个可能机制可能是由于黑潮的流动模式改变了这两个物种的生殖环境。事实上，有报道称，黑潮的非弯曲型更适合沙丁鱼，而大的黑潮弯曲型似乎更适合沙丁鱼。本文研究了黑潮弯曲对繁殖环境的影响，重点探讨了黑潮弯曲对繁殖环境的影响， ...更多信息 黑潮弯曲对海流场、温度和食物供应都有很大的影响，黑潮在中太平洋沿岸的大弯曲可能增强了鱼卵和仔稚鱼的近岸输送，也有助于沿岸产卵场和育苗场所在的陆架区的温度升高。这可能有利于沙丁鱼的招聘，因为沙丁鱼产卵更多的离岸和更依赖于产卵温度（15-17摄氏度）相比，沙丁鱼。值得注意的是，沙丁鱼只能在2月至3月期间产卵，只有在观察到大型黑潮弯曲的年份。另一方面，据透露，鱼的产卵更密切相关的透明度较低，这可能是沿海水域的流行，因此较高的食物供应，此外，通过大量的实地调查，还发现黑潮的卵和仔稚鱼在恩洲沿岸水域孵化，nada海可能被卷入与黑潮锋面相关的气旋性涡旋中，这可能为黑潮锋面的生物生产力提高提供了有利的摄食和幼体存活条件。少

In 1970s, Japanese anchovy population, particularly its spring spawners started to decline corresponding to the rapid increase of Japanese sardine population in the Enshu-nada Sea. The absence of predatory plankton and competitive pelagic fish such as anchovy during the main spawning period of the sardine (February-March) was apparently advantageous to recruitment success of the sardine. In late 1980s, sardine started to decline, being replaced by anchovy. It was noteworthy that during this phase the spawning period of the sardine was delayd a few months.One of the possible mechanisms behind the replacement could be the changes in the reproductive environment of these two species due to variations in the flow pattern of the Kuroshio. It has been, in fact, reported that anchovy preferred non meandering Kuroshio patterns, while large Kuroshio meander seemed favorable to sardine. We have investigated the influences of the Kuroshio meander on the reproductive environment, focusing on the c … More hanges in current fields, temperature and food availability due to the Kuroshio meander.The large meander of the Kuroshio off the central Pacific coast possibly enhances the inshore transport of fish eggs and larvae and also contributes to temperature increase in the shelf regions, where coastal spawning grounds and nurseries are located. This could favor the sardine recruitment because sardines spawn more offshore and are more dependent on the spawning temperature (15-17ﾟC) compared to anchovies. It shoud be noted that sardines could spawn during February-March only the years, when large Kuroshio meanders were observed. On the other hand, it is revealed that anchovy's spawning is more closely related to lower transparency, which may be indicative of coastal water prevalence and therefore higher food availability, frequently corresponding to non-meandering Kuroshio patterns.It has been also revealed from intensive field surveys that anchovy eggs and larvae hatched in the coastal water of the Enshu-nada Sea were possibly entrained into cyclonic eddies associated with the Kuroshio front, which could provide favorable conditions for feeding and larval survival due to the enhanced biological productivity. Less