Fisheries capture and infectious agents are associated with travel rate and survival of Chinook salmon during spawning migration

Abstract

Following interactions with fisheries gear, fishes may experience delayed mortality or display modified behavior. The physiological status of fish at the time of capture, including the presence of infectious agents, can also influence survival outcomes. To explore the relationship between capture, infectious agents and fate, we simulated gillnet capture on adult salmon returning to a hatchery, used quantitative PCR to quantify infectious agents in non-lethal gill biopsies, and determined longevity, migratory fate, and migration rate using radio telemetry. An accompanying holding experiment investigated the relationship between infectious agents and longevity. Gillnetted fish took longer to migrate than biopsy-only fish (median 3.8 versus 2.5 days), but there was no difference in survival or migratory success among treatment groups. Longevity for fish infected with a parasite, Cryptobia salmositica, was similar between the holding (median = 7.0 days) and telemetry (7.4 days) experiments and significantly lower than that of uninfected fish (17.4 days in telemetry experiment). Males were 5.1 times more likely to arrive at spawning grounds compared to females and also migrated faster. The impact of C. salmositica on adult Chinook salmon in our study was demonstrated at the molecular (genes), physiological (plasma variables), and organism (migratory success) levels. These results demonstrate an instance where sex and infection were better predictors of migratory fate than an experimentally applied capture experience.