结合耳石微尺度稳定同位素分析与数据同化模型估算日本海日本鳀鱼的洄游历史
Estimation of migrate histories of the Japanese sardine in the Sea of Japan by combining the microscale stable isotope analysis of otoliths and a data assimilation model
AI总结：
本研究结合耳石氧同位素剖面与海洋数据同化模型，重建日本海0龄日本鳀鱼早期洄游历史，揭示其北迁或深栖两种避温策略及南部环境对种群动态的关键影响。
摘要：
日本鳀鱼（Sardinops melanostictus）是一种分布于日本海（西北太平洋边缘海）的小型中上层鱼类。它是区域渔业的重要物种，但其在早期生命阶段的输送和洄游模式仍不清楚。本研究分析了2015年和2016年从日本海北部近海和南部沿岸地区采集的当年生（0龄）日本鳀鱼耳石的稳定氧同位素比值。通过比较终生同位素比值剖面与随时间变化的同位素景观，估算了地理分布的个体发育变化；该同位素景观利用海洋数据同化模型生成的温度和盐度场计算得到。在北部和南部地区采集的个体均在南部地区（九州西部近海）孵化并停留至6月下旬，此后可区分为两个类群：一类在浅层向北洄游，另一类在深层停留于南部地区附近。基于耳石微结构分析重建的两个类群的躯体生长轨迹比较表明，向北洄游的个体在6月下旬的体长显著大于停留在南部地区的个体。这些结果表明，在南部地区孵化的当年生日本鳀鱼可能在季节和地理限制下被迫选择两种策略之一，以避开极高水温：向北洄游或移动至更深层。研究结果表明，南部地区的环境变化可能对日本海的鳀鱼种群动态产生关键影响。
英文摘要：
The Japanese sardine (Sardinops melanostictus) is a small pelagic fish found in the Sea of Japan, the marginal sea of the western North Pacific. It is an important species for regional fisheries, but their transportation and migration patterns during early life stages remain unclear. In this study, we analyzed the stable oxygen isotope ratios of otoliths of young-of-the-year (age 0) Japanese sardines collected from the northern offshore and southern coastal areas of the Sea of Japan in 2015 and 2016. The ontogenetic shifts of the geographic distribution were estimated by comparing the profiles of life-long isotope ratios and temporally varying isoscape, which was calculated using the temperature and salinity fields produced by an ocean data assimilation model. Individuals that were collected in the northern and southern areas hatched and stayed in the southern areas (west offshore of Kyushu) until late June, and thereafter, they can be distinguished into two groups: one that migrated northward at shallow layer and one that stayed around the southern area in the deep layer. A comparison of somatic growth trajectories of the two groups, which was reconstructed based on otolith microstructure analysis, suggested that individuals that migrated northward had significantly larger body lengths in late June than those that stayed in the southern area. These results indicate that young-of-the-year Japanese sardines that hatched in the southern area may have been forced to choose one of two strategies to avoid extremely high water temperatures within seasonal and geographical limits. These include migrating northward or moving to deeper layers. Our results indicate that the environmental variabilities in the southern area could critically impact sardine population dynamics in the Sea of Japan.
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