Geology topics

Emma A. Elliott Smith

Publications and source records attributed to Emma A. Elliott Smith.

4 recordsLinked to original sources

USGS2026

Exploring the use of amino acid stable hydrogen isotope (δ2H) analysis to improve geographic assignment of wildlife

S table isotopes of hydrogen ( δ 2 H) have long been used to trace the movement and geographic origins of wildlife. δ 2 H analysis of individual amino acids (AA) offer a multivariate alternative to bulk tissue analysis, but the geographic resolving power of this approach remains underexplored. Here, we analyzed AA δ 2 H, along with bulk tissue δ 2 H, δ 13 C, and δ 15 N values of 32 feathers collected from Canada geese ( Branta canadensis ) with known molting locations along a latitudinal gradient in the Midwestern United States (34–48 °N). We evaluated isotopic variation among three latitudinally defined geographic groups across this gradient. The δ 2 H values of essential AA showed strong latitudinal separation, with isoleucine, leucine, and valine differing among all pairwise comparisons and exhibiting between-group differences exceeding those observed in bulk feather δ 2 H. In contrast, δ 2 H values of non-essential AA were far more variable within groups and, apart from proline and glutamic acid, did not exhibit significant differences among geographic localities. A bootstrapped flexible discriminant analysis (FDA) incorporating δ 2 H values of five essential AA yielded a mean classification accuracy of 82 %, with misclassification concentrated between adjacent North and Central groups. Including bulk tissue δ 13 C values marginally improved model accuracy (mean 83 %), likely reflecting geographic variation in native or agricultural C 4 plant abundance. An FDA model based only on non-essential AA δ 2 H values performed poorly (mean 59 % accuracy), which contrasts with recent studies on humans in which non-essential AA δ 2 H values were better predictors of region of origin. We suggest this discrepancy reflects differences in food sourcing; barring carry-over effects, wildlife primarily incorporate locally derived essential AA whereas human (supermarket) diets often integrate protein sources across continental spatial scales. Our results indicate that essential AA exhibit clear latitudinal structure in δ ²H values and hence these analyses offer strong potential for geographic assignment of migratory birds.

Isotopes in Environmental and Health Studies↗

USGS2025

Integrating marine historical ecology into management of Alaska’s Pacific cod fishery for climate readiness

The Pacific cod ( Gadus macrocephalus ) fishery was closed in 2020 after a rapid decline in biomass caused by the marine heat waves of 2014–2019. Pacific cod are exceptionally thermally sensitive and management of this fishery is now challenged by increasingly unpredictable climate conditions. Fisheries monitoring is critical for climate readiness, but short-term monitoring data may be inadequate for recognizing and anticipating change under rapid climate changes. We propose an interdisciplinary, marine historical ecology framework that looks to long-term records (local and traditional knowledge, history, archaeology, and paleoclimatology) to capture a long range of ecological variability and provide historical context for management. In order to connect to contemporary fisheries management, this framework must be built on a common vocabulary and an understanding of the key metrics used in fisheries stock assessments. Here, we propose metrics derived from Pacific cod stock assessment and synthesize information relevant to understanding the effects of past warming periods on cod populations across the Gulf of Alaska and Bering Sea. This case study provides a framework for thinking about how to use these historical records in the context of fisheries management under rapidly changing climate conditions.

Alaska↗

USGS2025

Forecasting sea otter recolonization: Insights from isotopic analysis of modern and zooarchaeological populations

Retrospective datasets offer essential context for conservation by revealing species’ ecological roles before industrial-era human impacts. We analysed isotopic compositions of pre-industrial and modern sea otters ( Enhydra lutris ) to reconstruct pre-extirpation ecology and offer insights for management. Our study focuses on southeast Alaska (SEAK), where sea otters are recolonizing, and northern Oregon, where translocations are being considered. We measured bulk bone collagen δ 13 C and δ 15 N values and essential amino acid δ 13 C values of extirpated sea otters from archaeological contexts, and bulk isotopic values from vibrissae of modern SEAK sea otters. We compare these results with published isotopic data of potential prey and additional archaeological datasets. In SEAK, our data show pre-industrial sea otter populations consumed infaunal bivalves and used soft-sediment (33%) and kelp forest habitats (67%), with sub-regional variation. We anticipate current populations will expand into this historical niche, and conflict with regional traditional/subsistence bivalve fisheries will persist. In northern Oregon, isotopic data from extirpated sea otters indicate past consumption of low trophic level invertebrates and a stronger reliance on kelp forests (88%) rather than soft-sediment habitats, highlighting the importance of kelp forests for future translocations. Our work exemplifies the value of historical ecology in informing conservation strategies for recovering species.

Alaska, Oregon↗

USGS2015

The cost of reproduction: differential resource specialization in female and male California sea otters

Intraspecific variation in behavior and diet can have important consequences for population and ecosystem dynamics. Here, we examine how differences in reproductive investment and spatial ecology influence individual diet specialization in male and female southern sea otters ( Enhydra lutris nereis ). We hypothesize that greater reproductive constraints and smaller home ranges of females lead to more pronounced intraspecific competition and increased specialization. We integrate stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope analysis of sea otter vibrissae with long-term observational studies of five subpopulations in California. We define individual diet specialization as low ratios of within-individual variation (WIC) to total population niche width (TNW). We compare isotopic and observational based metrics of WIC/TNW for males and females to data on population densities, and movement patterns using both general linear and linear mixed-effects models. Consistent with our hypothesis, increasing population density is associated with increased individual diet specialization by females but not by males. Additionally, we find the amount of coastline in a sea otter’s home range positively related with individual dietary variability, with increased range span resulting in weaker specialization for both males and females. We attribute our results to sex-based differences in movement, with females needing to specialize in their small ranges to maximize energy gain, and posit that the paradigm of individual prey specialization in sea otters with increased intraspecific competition may be a pattern driven largely by females. Our work highlights a potentially broader role of sex in the mechanistic pressures promoting and maintaining diet specialization.

California↗