Infections, fisheries capture, temperature, and host responses: multistressor influences on survival and behaviour of adult Chinook salmon

Infectious disease dynamics of wild Pacific salmon are poorly understood and may play a prominent role in recent declines of Chinook salmon (Oncorhynchus tshawytscha) populations. Multiple stressors influence migration success of adult salmon, such as rising river temperatures and capture and release by fisheries, and likely modulate infection development. To understand how these factors impact survival and migration behaviour of adult salmon in fresh water, we conducted simultaneous holding and telemetry studies with gillnet treatments and nonlethal biopsy. Laboratory fish were held and treated in either cool (9 degrees C) or warm (14 degrees C) water. High temperature reduced survival but did not amplify simulated gillnetting effects. Gillnetting reduced migration rate and distance traveled upriver and increased infection burdens, but had no effect on longevity. Heavy infections were associated with reduced longevity and faster migrations. Blood properties and immunity were associated with stressors, survival, and infections. These results improve our predictive capability regarding how stressors can reduce migration success and longevity of Pacific salmon, demonstrating multiple impacts of infections and adding to growing knowledge of disease dynamics in wild fish populations.