Isotopic values of sea otters (modern and archaeological) from Southeast Alaska and Northern Oregon and potential prey items from Southeast Alaska

Integrating pre-industrial datasets into management frameworks is critical
for establishing ecologically relevant baselines for conservation. Here,
we use isotopic analysis of archaeological and modern sea otter (Enhydra
lutris) specimens to anticipate future impacts of recolonization. We focus
on Southeast Alaska (SEAK) and northern Oregon, where sea otter
populations are recolonizing and competing with macroinvertebrate
fisheries or remain extirpated with translocations being considered,
respectively. We measured bulk bone collagen δ13C and δ15N and essential
amino acid δ13C values of archaeological sea otters, and bulk isotopic
values of vibrissae from modern SEAK sea otters. We compare these results
with data of potential prey and archaeological samples from California.
Isotopic data from SEAK reveal pre-industrial populations consumed
infaunal bivalves and utilized both soft-sediment (33%) and kelp forest
habitats (67%), with variation among sub-regions. If contemporary
populations expand into this historical niche, conflict with Indigenous
subsistence fisheries (bivalves) is likely to persist. Isotopic data of
archaeological sea otters from northern Oregon suggest past consumption of
low trophic level invertebrates, and a reliance on kelp forests (88%)
rather than soft-sediment habitats, underscoring the significance of kelp
forests for future translocations. Our work provides important
perspectives on the potential future ecology of a recovering keystone
predator.