Code for Aalto et al "Evidence of bluefin tuna (Thunnus thynnus) spawning in the Slope Sea region of the Northwest Atlantic from electronic tags"

Atlantic bluefin tuna (ABT) are large, wide-ranging pelagic predators which typically migrate between foraging regions in the North Atlantic and two principal spawning regions, the Gulf of Mexico and the Mediterranean Sea. A new spawning area has been described in the Slope Sea (SS) region off New England; however, the relationship between ABT that spawn in the SS and ABT using the principal spawning regions remains poorly understood. We used electronic tags to examine the location, temperature, and diving behavior of ABT in the SS, and identified 24 individuals that were present during the spawning season (June-August) with tag data showing temperatures and behavior consistent with spawning ABT. In general, the SS spawners had similar spatial ranges to Mediterranean-spawning ABT; however, some individuals displayed distinct behaviours that were identified first in Gulf of Mexico spawners. Using monthly spatial distributions, we estimated that the SS spawners have high exposure to fishing pressure relative to other ABT and may represent a disproportionate share of the West Atlantic catch. This analysis provides the first description of the behavior of ABT frequenting this spawning ground, creating a foundation for integrating this region into multi-stock management and, potentially, conserving an important source of genetic diversity.

大西洋蓝鳍金枪鱼（Atlantic bluefin tuna, ABT）是一类体型庞大、分布范围广泛的大洋洄游捕食者，通常在北大西洋觅食区与两处主要产卵场——墨西哥湾与地中海——之间进行长距离洄游。近期，科研人员在新英格兰外海的斜坡海（Slope Sea, SS）区域发现了一处新的产卵场，但针对在SS区域产卵的ABT与使用传统主要产卵场的ABT种群之间的关联，目前仍缺乏清晰的认知。本研究借助电子标记装置，对SS区域内ABT的栖息位置、所处水温及潜泳行为展开分析，共确认24尾在产卵季（6月至8月）出现的个体，其标记数据所反映的水温条件与行为特征均符合产卵个体的典型表现。总体而言，SS产卵群与地中海产卵群的空间活动范围较为相似，但部分个体展现出最初仅在墨西哥湾产卵群中被观测到的独特行为模式。通过月度空间分布数据，本研究估算得出：相较于其他ABT种群，SS产卵群面临的捕捞压力显著更高，且其在西大西洋捕捞总量中所占的比例或远超平均水平。本分析首次对栖息于该新型产卵场的ABT行为特征进行了系统性描述，为将该区域纳入多种群管理框架奠定了科学基础，并有望为保护这一重要的遗传多样性种群提供决策支撑。