Identification of infectious agents in early marine Chinook and Coho salmon associated with cohort survival

Recent decades have seen an increased appreciation for the role infectious
diseases can play in mass mortality events across a diversity of marine
taxa. At the same time many Pacific salmon populations have declined in
abundance as a result of reduced marine survival. However, few studies
have explicitly considered the potential role pathogens could play in
these declines. Using a multi-year dataset spanning 59 pathogen taxa in
Chinook and Coho salmon sampled along the British Columbia coast, we
carried out an exploratory analysis to quantify evidence for associations
between pathogen prevalence and cohort survival, and between pathogen load
and body condition. While a variety of pathogens had moderate to strong
negative correlations with body condition or survival for one host species
in one season, we found that Tenacibaculum maritimum and Piscine
orthoreovirus had consistently negative associations with body condition
in both host species and seasons, and were negatively associated with
survival for Chinook salmon collected in the fall and winter. Our
analyses, which offer the most comprehensive examination of associations
between pathogen prevalence and Pacific salmon survival to date, suggest
that pathogens in Pacific salmon warrant further attention, especially
those whose distribution and abundance may be influenced by anthropogenic
stressors.