DOI: 10.5061/dryad.6hdr7sr9j
title: Isotopic values of sea otters (modern and archaeological) from Southeast Alaska and Northern Oregon and potential prey items from Southeast Alaska

description: 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.
description: Bulk tissue <em>δ</em><sup>13</sup>C and
 <em>δ</em><sup>15</sup>N 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
 N<sub>2 </sub>. We report all isotopic data as
 <em>δ</em> values in parts per thousand, or per mil (‰), where
 <em>δ</em><sup>13</sup>C or
 <em>δ</em><sup>15</sup>N =
 1000*[(R<sub>samp</sub>/R<sub>std</sub>)
  1]. Here, R<sub>samp</sub> and
 R<sub>std</sub> are the
 <sup>13</sup>C:<sup>12</sup>C or
 <sup>15</sup>N:<sup>14</sup>N 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 <em>δ</em><sup>13</sup>C and
 <em>δ</em><sup>15</sup>N values. As a control for
 the quality of our collagen samples, we converted measured weight [C]:[N]
 to atomic ratios: [C]:[N]<sub>atomic</sub> =
 [C]:[N]<sub>weight</sub> ∗ (14/12). 
 The carbon isotope compositions of individual amino acids within
 a subset of archaeological sea otter samples (n=35) were measured via a
 gas chromatography-combustion system (GC-C; Thermo Scientific Trace 1310
 and Isolink II) coupled to an IRMS at UNM-CSI. Derivatized samples and
 in-house amino acid reference mixtures were dried down under a gentle
 stream of N<sub>2</sub> gas and brought up to final dilution
 in DCM. Sample DCM solutions were injected (1 mL) into a 60 m BPx5 gas
 chromatograph column (0.32 ID, 1.0 mm film thickness, SGE Analytical
 Science, Victoria, Australia) for amino acid separation (Trace 1310), and
 then combusted into CO<sub>2 </sub>gas (Isolink II). Isotopic
 ratios were analyzed with a Thermo Scientific Delta V IRMS. Samples were
 run in duplicate and bracketed with the in-house reference material; we
 report sample means across injections, and we discarded data where
 standard deviations &gt;1.2 ‰. We measured
 <em>δ</em><sup>13</sup>C values of 12 amino acids,
 six of which are considered essential – isoleucine (Ile), leucine (Leu),
 lysine (Lys), phenylalanine (Phe), threonine (Thr) and valine (Val), and
 six nonessential – alanine (Ala), aspartic acid/asparagine (Asx), glutamic
 acid/glutamine (Glx), glycine (Gly), hydroxyproline/proline (Pro), and
 serine (Ser). <em>We use only essential amino acid
 δ<sup>13</sup>C data for all statistical analyses in this
 text.</em> The reagents used during
 derivatization add carbon to the side chains of amino acids,
 and <em>δ</em><sup>13</sup>C values measured via
 GC-C-IRMS are thus a combination of intrinsic amino acid carbon and
 reagent carbon. However, because amino acid reference materials of known
 <em>δ</em><sup>13</sup>C composition were
 derivatized and run with each batch of samples, we were able to correct
 for this carbon addition for each amino acid (see equation 3 from
 O'Brien et al. (2002)). These corrections are done on a daily, or
 ‘per run’ basis, which means unknown samples are typically corrected using
 four to six bracketed injections of the in-house reference
 material. Reference: O'Brien, D. M., Fogel, M. L.,
 & Boggs, C. L. (2002). Renewable and nonrenewable resources: amino
 acid turnover and allocation to reproduction in
 Lepidoptera. <em>Proceedings of the National Academy of
 Sciences</em>, <em>99</em>(7), 4413-4418.
description: # 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 present times and present inferences into the future ecological patterns of this recovering keystone marine predator.  Reference: Newsome, S. D., Tinker, M. T., Gill, V. A., Hoyt, Z. N., Doroff, A., Nichol, L., & Bodkin, J. L. (2015). The interaction of intraspecific competition and habitat on individual diet specialization: a near range-wide examination of sea otters. *Oecologia*, *178*, 45-59. ### Files and variables File: EES_SEAK_OR_otters.xlsx **Description:** Four data tables included as separate tabs in a Microsoft Excel file.  * **Table S1. Isotopic data of archaeological sea otter specimens.** The data presented below are raw values determined via EA-IRMS and have not been adjusted for tissue or temporal-specific isotope differences. Notes on this table are included below: * Column "Age (calBP)" presents the time period of occupation in calendar years before present (1950) for a given archaeological context, and hence represent the provenance for a pre-industrial sea otter specimen. These ages are drawn from previous works reporting radiocarbon analyses. Refer to published manuscript for details and associated references.  * Column "Age" presents the likely age of each sea otter specimen based on osteological patterns. Codes are: Ad=adult, Al=likely adult, Ju=juvenile, Jl=likely juvenile, Pp=pup, Uk=unknown. * Specimens with "n/a" in field 'Side' are those where elements measured were either not sided (e.g., vertebrae), or side could not be determined (e.g., ribs).  * Specimens with 'nd' in fields '*δ*13C' and '*δ*15N' are those which disintegrated during demineralization and were not analyzed for bulk *δ*13C and *δ*15N. * Column "AA" denotes specimens for which we measured bulk tissue isotopic values (*δ*13C, *δ*15N) as well as *δ*13C values of individual amino acids.  * Column "[C]:[N]atomic" reports quality control metrics for archaeological specimens. Values &gt;= 3.8 indicate the sample had diagenetic alteration and the isotopic values for these samples were not used in any statistical analyses.  * Regional abbreviations: Northern Oregon coast, (N OR), southeast Alaska (SEAK). * **Table S2. Isotopic data for modern sea otters from southeast Alaska.**  These data from isotopic analyses of modern sea otter vibrissae (whiskers) by Newsome et al. (2015), with sample sizes (column ‘N’) representing the number of segments analyzed from each vibrissae for each individual. The data presented below are raw values determined via EA-IRMS and have not been corrected for tissue or temporal-specific isotope differences * Source [1] = Newsome et al. 2015 * Column 'N' here refers to the number of whisker (vibrissae) segments measured for each individual and averaged to give columns "Mean *δ*13C" and "Mean *δ*15N" * **Table S3. Isotopic data of potential macroinvertebrate prey species in southeast Alaska.** Isotopic analysis of modern sea otter prey by Newsome et al. (2015), though we present updated scientific names here; all data presented and used here come from specimens which were lipid extracted. * Source [1] = Newsome et al. 2015 * Column 'N' here refers to the number of individuals measured and averaged to give columns "*δ*13C (mean +/- sd)" and "*δ*15N (mean +/- sd)" * **Table S6. Amino acid *δ*13C values of archaeological sea otter specimens.**  * Amino acid abbreviations: alanine (Ala), aspartic acid (Asp), glutamic acid (Glu), glycine (Gly), proline (Pro), serine (Ser), isoleucine (Ile), leucine (Leu), lysine (Lys), phenylalanine (Phe), threonine (Thr), valine (Val). Note that only essential amino acid data were used in the published manuscript.  * Regional abbreviations: Northern Oregon coast, (N OR), southeast Alaska (SEAK). Reference: Newsome, S. D., Tinker, M. T., Gill, V. A., Hoyt, Z. N., Doroff, A., Nichol, L., & Bodkin, J. L. (2015). The interaction of intraspecific competition and habitat on individual diet specialization: a near range-wide examination of sea otters. *Oecologia*, *178*, 45-59. ## Access information Other publicly accessible locations of the data: * In published journal article as supplemental materials.  Data was derived from the following sources: * Newsome, S. D., Tinker, M. T., Gill, V. A., Hoyt, Z. N., Doroff, A., Nichol, L., & Bodkin, J. L. (2015). The interaction of intraspecific competition and habitat on individual diet specialization: a near range-wide examination of sea otters. *Oecologia*