Abstract
Rare species are difficult to observe in the wild, particularly in the ocean where large spatial scales and accessibility hinder effective sampling. Environmental DNA (eDNA) is a non-destructive, scalable sampling method with the potential to inform the distribution of rare species in marine ecosystems. We sample eDNA within the California Current ecosystem to estimate the distribution of eulachon (Thaleichthys pacificus), a threatened anadromous smelt ranging along the coastal Northeast Pacific. We amplify eulachon DNA from thousands of water samples collected at night across two years and more than 200,000 square kilometers along the U.S. west coast. We then use spatiotemporal models to derive quantitative estimates of eulachon DNA across space, depth, and time relative to environmental covariates. We find that eulachon DNA has a distribution weighted towards the ocean surface, spatially associated with major river mouths and productive offshore banks. Temperature and prey density are key covariates, with eulachon more likely to be found in warmer waters with higher prey concentrations. We discuss how our results can augment the information currently used in eulachon recovery planning, and describe the wide applicability of our statistical models for estimating distribution and abundance for other species of conservation concern.
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Data availability
All data and code required to reproduce our findings are archived and publicly available on Zenodo (https://doi.org/10.5281/zenodo.14721413). The source data behind the figures in the paper are available in the Zenodo archive. No genetic sequence data were generated in this study. All genetic analyses were performed via quantitative PCR (qPCR) using established, previously published primer sequences in Ramón-Laca et al.15 (also in Table 1) to quantify the expression of known targets, resulting in numerical data rather than producing sequence reads. Any remaining information can be obtained from the corresponding author upon reasonable request.
Code availability
The R code required to reproduce our findings are archived with the study data on Zenodo (https://doi.org/10.5281/zenodo.14721413).
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Acknowledgements
The authors gratefully acknowledge the survey expertise and support of NOAA’s Pacific Hake survey team and the NOAA Ship Bell M. Shimada personnel for supporting the collection of eDNA samples on the West Coast Hake Survey 2019-2021. In addition, the authors acknowledge L. Park and R. Gustafson for their leadership in the early stages of the development of this study; without their support this work would not have been possible. This work was supported in part by the NOAA Fisheries Omics Strategic Initiative (2019-2023).
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Conceptualization: O.R.L., A.O.S., K.M.N., and R.P.K. Methodology: O.R.L., A.O.S., R.P.K., and E.J.W. Data analysis: O.R.L. and E.J.W. Data curation: A.R.-L., A.O.S., K.M.N., R.P.K., E.M.P., and A.W. Writing and editing: O.R.L., A.O.S., A.R.-L., K.M.N., E.J.W., E.M.P., J.E.Z., A.W., and R.P.K.
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Communications Biology thanks Mads Reinholdt Jensen, Cristina Claver, and the other anonymous reviewers for their contribution to the peer review of this work. Primary handling editors: Linn Hoffmann, Aylin Bircan, and Rupali Sathe. A peer review file is available.
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Liu, O.R., Shelton, A.O., Ramón-Laca, A. et al. Mapping the marine distribution of eulachon (Thaleichthys pacificus) in the Northeast Pacific using environmental DNA. Commun Biol (2026). https://doi.org/10.1038/s42003-026-09733-5
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DOI: https://doi.org/10.1038/s42003-026-09733-5
