Disappearance of Icelandic Walruses Coincided with Norse Settlement

Abstract

There is a growing body of evidence demonstrating the impacts of human arrival in new "pristine" environments, including terrestrial habitat alterations and species extinctions. However, the effects of marine resource utilization prior to industrialized whaling, sealing, and fishing have largely remained understudied. The expansion of the Norse across the North Atlantic offers a rare opportunity to study the effects of human arrival and early exploitation of marine resources. Today, there is no local population of walruses on Iceland, however, skeletal remains, place names, and written sources suggest that walruses existed, and were hunted by the Norse during the Settlement and Commonwealth periods (870-1262 AD). This study investigates the timing, geographic distribution, and genetic identity of walruses in Iceland by combining historical information, place names, radiocarbon dating, and genomic analyses. The results support a genetically distinct, local population of walruses that went extinct shortly after Norse settlement. The high value of walrus products such as ivory on international markets likely led to intense hunting pressure, which-potentially exacerbated by a warming climate and volcanism-resulted in the extinction of walrus on Iceland. We show that commercial hunting, economic incentives, and trade networks as early as the Viking Age were of sufficient scale and intensity to result in significant, irreversible ecological impacts on the marine environment. This is to one of the earliest examples of local extinction of a marine species following human arrival, during the very beginning of commercial marine exploitation.

Keywords: Odobenus rosmarus; Viking Age; exploitation; extinction; human impacts; palaeogenetics.

Fig. 1.

Location (inset map) and age (graph) of Icelandic samples with successful radiocarbon dates included in this study (n = 34). Graph: Horizontal bars show represent 95.4% confidence intervals of marine reservoir corrected radiocarbon dates for all successfully dated Icelandic samples (y axis). Dates on the x axis are presented as both calibrated years BP (1950 AD) (top row) and calendar dates (bottom row). Midpoint range across all samples is 1290–8599 years BP. The black vertical dashed line represents Icelandic settlement around 870 AD (1080 BP). Bars are color coded based on age and correspond with sample dots on the map indicating collection localities. Map: Localities of sample provenance are indicated by colored points. Any overlapping points are offset by cluster grouping (indicated by a central black dot and overlapping circles displayed in a surrounding circle).

Fig. 2.

Map showing the locations of 224 finds of walrus skeletal remains in Iceland recorded since 1676. The insert box (right) represents a magnified area of localities with the most finds. Overlapping dots are clustered and the number of dots reduced to a single point is included as a value within the circle. Four main regions and place names mentioned in the text are labeled in the inset box.

Fig. 4.

Haplotype network from SANGER-sequenced newly generated and previously published mitochondrial CR sequences. Circles are color-coded according to the geographic origin of samples (coloration corresponds with fig. 3). Icelandic samples fall into a cluster of eight unique haplotypes (circle by a dashed line). Only samples with a maximum of one missing or ambiguous base were included to avoid erroneous haplotype assignment. Haplotype assignment was repeated for samples with missing data for a shortened region of the mitochondrial CR, resulting in eight of the nine previously unassigned samples sharing one of the second most common Icelandic haplotypes.

Fig. 3.

Bayesian phylogeny of newly generated and previously published entire mitochondrial genomes (minus D-loop). Dots are color coded based on the sample’s geographic region, corresponding to the inset map, based upon the current distribution and stock structure of Atlantic walrus. Black dots represent archaeological rostrums found in institutional collections by Star et al. (2018) of unknown geographic affinity represented simplistically on the map as originating from numerous locations across continental Europe. Clades were collapsed when posterior probabilities were <0.2 or only samples from a single locality were found (excluding Iceland for which all branches were retained). The value within a circle represents the numbers of samples from that same region found within the collapsed clades. The horizontal accumulation of circles indicates multiple samples from different regions within a collapsed clade. Tip placement with respect to the x axis indicates approximate ages as midpoint estimates (cal. years BP). Branches in bold represent nodes with poster probabilities of 1.0. All other posterior probabilities are labeled at nodes.