Graduate Thesis Or Dissertation


Spatial and Temporal Dynamics of Eulachon (Thaleichthys pacificus) in Northern Southeast Alaska Public Deposited

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  • In Southeast Alaska, Eulachon (Thaleichthys pacificus) are a culturally and biologically important anadromous fish. Eulachon populations have significantly declined in the southern part of their range, and in 2010 eulachon in northern California, Oregon, and Washington were listed as a threatened species under the Endangered Species Act. In the same year, the Chilkoot Indian Association and Takshanuk Watershed Council began a mark-recapture study on the Chilkoot River near Haines, Alaska to assess eulachon population size and trend. Such assessment is critical to resource management, but can be too logistically challenging and expensive to incorporate on long temporal or large spatial scales. In 2014 through a partnership with Oregon State University, we initiated daily environmental DNA (eDNA) sampling to assess whether this could serve as a more economical and reliable method for long-term population monitoring. In 2017 the use of eDNA to document population size and trends was expanded to 8 rivers within northern southeast Alaska. We examined the relationship between five years of mark-recapture population estimates and eDNA rates derived from droplet digital PCR at the Chilkoot River and two years of regional eDNA rates across the region. The eDNA rate was assessed in two forms; the peak of the eDNA rate and the area under the curve. Both the peak eDNA rate and area under the curve of the eDNA rate were highly predictive of the mark-recapture population estimate, explaining 84% and 90% of the variance respectively. The regional eDNA assessment provided the first glimpse of how eulachon populations fluctuate across space and time within northern southeast Alaska. The peak of eDNA concentration indicated a strong north-south latitudinal gradient across the region, signifying that eulachon spawning aggregations fluctuate as a resource wave within the region allowing for elongated predator foraging opportunity. These results support the use of eDNA to monitor eulachon population trends and represent a >80% cost savings over mark-recapture, which could be further increased with automated water sampling. Due to the logistical ease and affordability of eDNA sampling, this method can facilitate monitoring a larger number of rivers and in remote locations where other methods are infeasible.
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  • Pochardt, M., et al (2019) Spatial and Temporal Dynamics of Eulachon (Thaleichthys pacificus) in Northern Southeast Alaska.
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