Handling, infectious agents and physiological condition influence survival and post-release behaviour in migratory adult coho salmon after experimental displacement.

K M Miller,A L Bass,A K Teffer,J M Chapman,D A Patterson,S G Hinch,S J Cooke,Craig Franklin

doi:10.1093/conphys/coaa033

K M Miller, A L Bass + Show 6 more

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https://doi.org/10.1093/conphys/coaa033

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Abstract

For Pacific salmon captured and released by fisheries, post-release behaviour and survival may be influenced by their health and condition at time of capture. We sought to characterize the interactions between infectious agent burden, fish immune and stress physiology and fisheries stressors to investigate the potential for capture-mediated pathogen-induced mortality in adult coho salmon Oncorhynchus kisutch. We used radio-telemetry paired with high-throughput qPCR of non-lethal gill biopsies for infectious agents and host biomarkers from 200 tagged fish experimentally displaced and exposed to various experimental fisheries treatments (gill net entanglement, recreational angling and recreational angling with air exposure vs. non-sampled control). We characterized relationships among post-release behaviour and survival, infectious agent presence and loads, physiological parameters and transcription profiles of stress and immune genes. All infectious agents detected were endemic and in loads consistent with previous adult Pacific salmon monitoring. Individuals exposed to fisheries treatments were less likely to reach spawning habitat compared to controls, and handling duration independent of fisheries gear had a negative effect on survival. High infectious agent burden was associated with accelerated migration initiation post-release, revealing behavioural plasticity in response to deteriorating condition in this semelparous species. Prevalence and load of infectious agents increased post-migration as well as transcription signatures reflected changes in immune and stress profiles consistent with senescence. Results from this study further our understanding of factors associated with fisheries that increase risk of post-release mortality and characterize some physiological mechanisms that underpin migratory behaviour.

Highlights

Associations among pathogens and their hosts in wildlife populations are relevant to conservation efforts but remain relatively under-studied due to logistical constraints (Grenfell et al 1995)
The observed up-regulation of SHOP21 and C7 post-migration corresponding with downregulation of MHCII-B may be in response to disease associated osmotic stress resulting from increased infection burden and decreased immunocompetency. These results indicate the synergistic trajectory of natural senescence and disease ecology in Pacific salmon and highlight the challenges associated with teasing apart causal relationships among gene expression, stress physiology and the numerous infectious agents carried by wild salmon in the final stages of freshwater migration
Recent evidence suggests a role of infectious agents in mediating post-release survival (Bass et al 2017; Patterson et al 2017; Teffer et al 2017), and our results support an influence of cumulative infection profiles on migratory delay following capture and release

Summary

Introduction

Associations among pathogens and their hosts in wildlife populations are relevant to conservation efforts but remain relatively under-studied due to logistical constraints (Grenfell et al 1995). Surveys of infective agents in aquatic wildlife populations generally investigate relatively rare events or anomalies and do not assess infectious agents in the context of general ecology and conservation (Miller et al 2014). As aquatic ecosystems continue to experience change as a result of human activities (Dudgeon et al 2006; Reid et al 2019), it is increasingly necessary to characterize pathogen dynamics outside of aquaculture and episodic disease events to focus instead within the context of ‘natural’ pathogen dynamics and impacts of anthropogenic stressors. As infectious disease is often believed to be the ultimate cause of mortality in stressful environments (Joseph et al 2013; Miller et al 2014) and stressors rarely occur in isolation outside of laboratory settings, it is necessary to investigate synergistic effects of multiple stressors when considering stress in wild organisms (Crain et al 2008)

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