Biomarkers of mortality risks in Yukon Chinook salmon

We will leverage a multiagency study focused on Ichthyophonus using lethally collected heart tissue beginning in summer 2022 as a rare opportunity to investigate Ichthyophonus and heat stress jointly in the same individuals. This proposal seeks funds to (1) estimate heat stress prevalence using previously validated biomarkers (HSP70 protein and gene transcription) to provide a more comprehensive premature mortality risk index that combines heat stress and Ichthyophonus and (2) investigate feasibility of using skeletal muscle tissue gene transcripts (mRNA of select genes) to differentiate individuals with clinical Ichthyophonus disease from those without Ichthyophonus or with mild, subclinical infections unlikely to compromise survival. We previously validated the use of non-lethal muscle biopsies to assess heat stress and hypothesize that mRNA profiles of salmon genes may also correlate to clinical Ichthyophonus disease because the disease is associated with cardiac damage and reduced swimming stamina that likely affect skeletal muscle. If biomarkers of clinical Ichthyophonus disease exist in muscle tissue, then a single non-lethal muscle biopsy punch could be used to index premature mortality risk in future years. This proposal represents an important step toward integrating drivers of freshwater mortality in a multiple stressors framework.

Premature mortality of spawning adult Pacific salmon (Oncorhynchus species) can strongly influence population dynamics and thwart escapement-based management if individuals entering the river frequently die prior to spawning. Heat stress and Ichthyophonus disease have been identified as probable drivers of premature mortality in Yukon River Chinook salmon and likely contributors to low abundance.