Graduation Date
Spring 2024
Document Type
Thesis
Program
Master of Science degree with a major in Natural Resources, option Fisheries
Committee Chair Name
Andrew Kinziger
Committee Chair Affiliation
HSU Faculty or Staff
Second Committee Member Name
Eric Bjorkstedt
Second Committee Member Affiliation
HSU Faculty or Staff
Third Committee Member Name
Andre Buchheister
Third Committee Member Affiliation
HSU Faculty or Staff
Keywords
eDNA, Environmental DNA, Tracer, Coho salmon, Steelhead, Streams
Subject Categories
Fisheries
Abstract
This study was motivated by the need to develop a noninvasive and highly sensitive monitoring tool for determining local occupancy of an endangered aquatic species To make inference into the occupancy of fishes within small stream sites, we developed a method to determine whether environmental DNA (eDNA) concentrations from a target species were elevated relative to a tracer, formulated to mimic eDNA and introduced at a single location. We examined patterns in the observed distribution of the tracer to account for the effects of site-specific transport processes and sampling on distributions of naturally occurring eDNA at small spatial scales (400 meters). Concentrations of two tracers, introduced at high and low concentrations, and eDNA from two target species, coho salmon (Oncorhynchus kisutch) and steelhead (Oncorhynchus mykiss), were simultaneously surveyed in eight study sites across a range of spatial scales (100-400 m). Target species were observed in all study sites during snorkel surveys, thus the expectation was detection of both species, and non-detection would indicate situations where this method required refinement. In total, 128 occupancy assessments were conducted across all study sites, spatial scales, tracers and targets. In 41.4% of assessments, the ratio of target eDNA to tracer significantly increased, providing evidence for additional sources of target eDNA in the study sites (target presence). Using a higher concentration tracer resulted in an increased number of eDNA detections for both targets (51.6%), compared to the low concentration tracer (31.2%), due in part to the broader range over which the higher concentration tracer could be detected. Spatial scale was identified as a crucial factor for species detection, with higher detection rates (63-88%) in assessments conducted on samples separated by 300-400 m, than for samples separated by 100-200 m (25-38%). This study presents a novel approach employing an eDNA tracer to enable species detection in a non-invasive manner at small spatial scales, emphasizing the utility of using a tracer to account for site-specific transport processes. The approach implemented herein was effective with high concentration tracers and at larger spatial scales, but before the approach could be effectively implemented for conservation and management a more diverse set of environmental factors and occupancy scenarios should be explored to evaluate false positive and false negative detection rates.
Citation Style
Transactions of the American Fisheries Society
Recommended Citation
Bandy, Gavin B., "Evaluating the utility of tracers to characterize environmental DNA transport and inform detection of fishes in small streams" (2024). Cal Poly Humboldt theses and projects. 727.
https://digitalcommons.humboldt.edu/etd/727