Data from: Rewriting the history of an extinction - was a population of Steller's sea cows (Hydrodamalis gigas) at St. Lawrence Island also driven to extinction?

In one of the most infamous recent anthropogenic extinctions, the Kommandorskiye Islands population of Steller’s sea cow (Hydrodamalis gigas) was extirpated ca. 1768 CE. Until now, Steller’s sea cow was thought to be restricted in historic times to Bering and Copper Islands, Russia, with other records in the last millennium from the western Aleutian Islands. However, Steller’s sea cow bone has been obtained by the authors from St. Lawrence Island, Alaska, which is significantly farther north. Bone identity was verified using analysis of mitochondrial DNA. The stable isotope levels were obtained and the nitrogen-15 (δ15N)/ carbon-13 (δ13C) values for bone samples from St. Lawrence Island were significantly (p ≤ 0.05) different from Bering Island samples, indicating a second population. The bone samples were dated to between 1030 and 1150 BP (BP= Before Present or approximately 800 - 920 CE). The samples date from close to the beginning of the medieval warm period which could indicate that the population at St. Lawrence Island was driven to extinction by climate change which may have changed the availability of kelp or by expansion of the Inuit from the Bering Strait region, possibly due to opening waterways, maybe following bowhead whales (Balaena mysticetus), or possibly searching for mineral resources, like iron. This study provides evidence for a previously unknown population of sea cows in the North Pacific within the past 1000 years and a second Steller’s sea cow extirpation event in recent history.

在近代最臭名昭著的人为灭绝事件之列，科曼多尔群岛（Kommandorskiye Islands）的斯特勒海牛（Steller’s sea cow, Hydrodamalis gigas）种群于公元1768年左右被彻底灭绝。长期以来，学界普遍认为历史时期内斯特勒海牛仅局限分布于俄罗斯白令岛与科珀尔岛，近千年来的其他分布记录仅见于西阿留申群岛。然而，本研究团队从阿拉斯加圣劳伦斯岛（St. Lawrence Island）采集到了斯特勒海牛的骨骼样本，该岛屿的纬度远高于此前已知的分布范围。研究通过线粒体DNA（mitochondrial DNA）分析验证了该骨骼的物种归属。研究测定了骨骼样本的稳定同位素组成，结果显示圣劳伦斯岛样本的氮-15（δ¹⁵N）与碳-13（δ¹³C）值与白令岛样本存在显著差异（p ≤ 0.05），表明存在另一支独立的海牛种群。经放射性碳测年，这批骨骼样本的年代为距今1030至1150年（BP即“距今年代”，以1950年为基准，对应公元800至920年左右）。这批样本的年代接近中世纪暖期的起始阶段，这提示圣劳伦斯岛的斯特勒海牛种群可能因气候变化导致巨藻（kelp）可获取量下降而灭绝；也可能是由于白令海峡地区航道开通，伴随弓头鲸（Balaena mysticetus）迁徙而来的因纽特人（Inuit）扩张，或是人类为寻找铁矿等矿产资源的活动，最终导致该种群走向灭绝。本研究为过去1000年间北太平洋存在此前未被发现的斯特勒海牛种群提供了实证支撑，同时也揭示了近代史上第二次斯特勒海牛种群灭绝事件。