The morphology, isotopic ecology, and phylogeny of walrus, Odobenus rosmarus (Pinnipedia: Odobenidae) populations

Walruses are classified into nine extant and two extirpated populations across their circumpolar distribution. While there are hints that these differ morphologically, thus far there has been no in-depth comparison of their morphology and ecology, limiting insights into their conservation and evolutionary status. Here, we investigate regional differences in walrus morphology and ecology during the 17th–21st centuries ce by integrating morphometric analysis of crania (N = 188) and mandibles (N = 193), multi-isotope analysis of bone collagen (δ13C, δ15N, and δ34S; N = 142), and genetic analysis (N = 115). The Pacific and Atlantic subspecies show morphological and isotopic distinctions. Distinct regional selection pressures on males and females can be inferred. This was most visible in the extirpated Maritimes walrus, where females had a unique cranium shape. Regional isotopic and genetic differences were also observed; we found regional differences in δ13C, δ15N, and δ34S, and identified multiple genetic clades coinciding with geographic populations. Overall, the comparative insight into the morphological, ecological, and genetic characteristics of different walrus populations sets a frame of reference for conservation management and from which to understand how each has been impacted by human exploitation and environmental changes in the past.