Fig. 2. PRV-1 infection dynamics in farmed Atlantic and wild Chinook salmon.

(A) Proportion of PRV-1–positive BC Atlantic salmon aquaculture audit samples (n = 664) versus time in saltwater. Points show the prevalence in each farm sample, scaled by sample size. Points colored blue contained a sample that was sequenced for phylogenetic analysis. The black curve is the fit of a Bayesian mixed-effects logistic model; almost all individuals on a farm become infected over the course of an 18-month grow-out period. Dark blue shading shows 95% credible interval (CI) of the mean logistic trend, and light blue shading shows 95% credible region including hierarchical variability from sampling events, farms, and aquaculture management zones. (B and C) The probability of PRV infection for first–marine-year Chinook salmon increases closer to active salmon farms in the fall-winter period, but not in the spring-summer. Chinook salmon (n = 4979) were captured by trawl and seine from 2008 through 2018 in coastal BC. Points (scaled by sample size) indicate the proportion of Chinook that were positive for PRV at varying distances from active aquaculture (2-km bins). Points colored blue contained a sample that was sequenced for phylogenetic analysis. The black curve is the fit of a Bayesian mixed-effects logistic model with random effects for regional population groupings and ocean entry year. Dark blue shading shows 95% CI for mean trends, and light blue shading shows 95% credible region, including hierarchical variation from ocean entry year and population grouping.