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?

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 further north. Bone identity was verified using analysis of
mitochondrial DNA. 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. Bone samples
were dated to between 1030 and 1150 BP (approx. 800–920 CE). The samples
date from close to the beginning of the mediaeval warm period, which could
indicate that the population at St Lawrence Island was driven to
extinction by climate change. A warming of the climate in the area may
have changed the availability of kelp; alternatively or in addition, the
animals may have been driven to extinction by the expansion of the Inuit
from the Bering Strait region, possibly due to opening waterways, maybe
following bowhead whales (Balaena mysticetus), or searching for iron and
copper. 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.