Natal origin of Pacific bluefin tuna from the California current large marine ecosystem

Natal origin of subadult (age-1) Pacific bluefin tuna (PBT, Thunnus orientalis) from the California Current Large Marine Ecosystem (CCLME) was determined using natural tracers in ear stones (otoliths). Age-0 PBT collected from the two known spawning areas in the western Pacific Ocean (East China Sea, Sea of Japan) were used to establish baseline signatures from otolith cores over four years (2014-2017) based on a suite of trace elements (Li, Mg, Mn, Sr, Zn, and Ba). Distinct chemical signatures existed in the otolith cores of age-0 PBT collected from the two spawning areas, with overall classification accuracy ranging from 73-93% by year. Subadult PBT collected in the CCLME over the following four years (2015-2018) were then age-class matched to baselines using mixed-stock analysis. Natal origin of trans-Pacific migrants in the CCLME ranged from 43-78% from the East China Sea and 22-57% from the Sea of Japan, highlighting the importance of both spawning areas for PBT in the CCLME. This study provides the first estimates on the natal origin of subadult PBT in this ecosystem using otolith chemistry and expands upon the application of these natural tracers for population connectivity studies for this species.

本研究利用耳石（ear stones，otoliths）中的天然示踪剂，确定了加利福尼亚洋流大型海洋生态系统（California Current Large Marine Ecosystem，CCLME）内1龄亚成体太平洋蓝鳍金枪鱼（Pacific bluefin tuna，PBT，Thunnus orientalis）的原产地。研究以2014—2017年四年间，从西太平洋两处已知产卵场（东海、日本海）采集的0龄太平洋蓝鳍金枪鱼为基准材料，基于锂（Li）、镁（Mg）、锰（Mn）、锶（Sr）、锌（Zn）及钡（Ba）等一系列微量元素，建立了耳石核心的化学特征基线。两处产卵场的0龄太平洋蓝鳍金枪鱼耳石核心具有显著差异化的化学特征，按年份划分的整体分类准确率为73%—93%。随后，研究通过混合种群分析（mixed-stock analysis），将2015—2018年四年间在CCLME内采集的亚成体太平洋蓝鳍金枪鱼按年龄层级与上述特征基线进行匹配。结果显示，该生态系统内跨太平洋洄游个体的原产地占比为：东海来源个体43%—78%，日本海来源个体22%—57%，凸显了两处产卵场对CCLME内太平洋蓝鳍金枪鱼种群的重要性。本研究首次利用耳石化学特征估算了该生态系统内亚成体太平洋蓝鳍金枪鱼的原产地，拓展了这类天然示踪剂在该物种种群连通性研究中的应用。