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..., Bulk tissue δ13C and δ15N values, along with weight percent [C] and [N], were measured via EA-IRMS using a Costech 4010 elemental analyzer (Valencia, CA) coupled to a Thermo Scientific Delta V Plus isotope ratio mass spectrometer (Bremen, Germany) at the University of New Mexico Center for Stable Isotopes (UNM-CSI; Albuquerque, NM). All samples and reference materials were calibrated against the internationally accepted standards for stable carbon and nitrogen isotope ratios, respectively Vienna-Pee Dee Belemnite (V-PDB) and atmospheric N2 . We report all isotopic data as δ values in parts per thousand, or per mil (‰), where δ13C or δ15N = 1000*[(Rsamp/Rstd)  1]. Here, Rsamp and Rstd are the 13C:12C or 15N:14N ratios of the sample and standard, respectively. The standard deviations of organic in-house reference materials (milk casein and tuna muscle) were 0.2 ‰ for both δ13C and δ15N values. As a control for the quality of our collagen samples, we converted measured weight [C]:[N] to at..., , # Isotopic values of sea otters (modern and archaeological) from Southeast Alaska and Northern Oregon and potential prey items from Southeast Alaska

[https://doi.org/10.5061/dryad.6hdr7sr9j](https://doi.org/10.5061/dryad.6hdr7sr9j)

## Description of the data and file structure

In this work, we measured isotopic compositions of modern and archaeological sea otters, and modern prey items. Our samples come from two geographic regions - southeast Alaska (SEAK) and northern Oregon. The data included here include a combination of bulk tissue d13C and d15N measurements (e.g., whole collagen samples, sub-sampled whiskers) as well as d13C values of individual amino acids from archaeological specimens. Some of the isotopic data from modern SEAK sea otters and their prey come from a previous publication (Newsome et al. 2015), and this is noted in the relevant data tables. Using these data, we characterized the dietary and habitat niche of sea otters prior to the maritime fur trade and in prese...