PhD funding to evaluate thermal tolerance of summer steelhead (Oncorhynchus mykiss)

Award Period
Award Amount
Agency Name
Award Number
PI First Name
PI Last Name
Eliason Parsons
MSI People
Area/s of Research
Ecology and Evolution

Steelhead (Oncorhynchus mykiss) have an expansive range and are one of the most diverse and adaptable of the six Pacific salmon species. Life history diversity can improve the resilience of a species, with multiple pathways to persistence. However, climate changes resulting in rising year-round temperatures and hydrological regime shifts are threatening this species. "Summer-run" steelhead arrive as immature adults to freshwater in late spring, migrating through warm river corridors, utilizing cool tributaries as thermal refugia. They often spend up to 6-9 months maturing into freshwater before spawning the following spring. The juvenile offspring then rear in freshwater for up to 1 year before out-migrating to the ocean the following spring. As a result of this protracted freshwater residence, this species is exposed to lethal temperatures. While we have thresholds denoting the thermal tolerance of this species, the data is generalized to the species, is based on laboratory studies, and does not indicate the variability amongst populations. Given this species' expansive range, we hypothesize that thermal tolerance varies with the thermal history to which the species has been exposed. Being able to allocate risk differentially across summer steelhead populations will enable better management of this species by allowing basin specific, science-based management decisions. This funding will support 1 quarter for Terra Dressler, a current PhD student at the University of California, Santa Barbara, who has been studying summer steelhead across their range in conjunction with ODFW. The funding will ensure that data processing, analytics, manuscript prep are completed in a timely manner so we can begin to make recommendations in the summer of 2023 for this already imperiled native species.

The funds will pay for her time (September-December) to process, clean, and analyze field respirometry data (collected in the summer of 2022 from the Deschutes and North Umpqua in Oregon) and prepare the results for a manuscript. At the end of the contract, the manuscript will be in suitable draft form and ready to be submitted to a peer-reviewed journal. She will incorporate existing data from two populations in southern California (Arroyo Seco, Piryu) and two populations in Oregon (John Day, Siletz) with the new data collected in Oregon in 2022 (Deschutes, Umpqua).