Environmental DNA from multiple pathogens is elevated near active Atlantic salmon farms

Area of Science:

• Aquatic ecology
• Marine biology
• Pathogen surveillance

Background:

• Infectious disease spread from reservoir hosts is critical for disease emergence and extinction risks.
• Salmon aquaculture and fisheries management face challenges from pathogen transmission.
• Understanding pathogen dynamics in marine environments is crucial for conservation.

Purpose of the Study:

• To assess pathogen environmental DNA (eDNA) prevalence in relation to salmon farms in coastal British Columbia.
• To investigate the association between pathogen eDNA detection and active versus inactive salmon farm sites.
• To determine if domesticated Atlantic salmon influence pathogen eDNA detection.

Main Methods:

• Utilized quantitative environmental DNA (eDNA) methodology.
• Tested 134 marine environmental samples from 58 salmon farm sites (active and inactive) over 3 years.
• Screened for 39 species of salmon pathogens (viral, bacterial, and eukaryotic).

Main Results:

• Detected eDNA from 22 pathogen species across 496 instances.
• Pathogen occurrence varied by year and site, influenced by environmental factors and host species.
• Pathogen eDNA detection probability was 2.72 times higher at active salmon farm sites compared to inactive ones.
• Pathogen eDNA detection increased by 1.76 times per standard deviation increase in Atlantic salmon eDNA concentration.

Conclusions:

• Salmon farms may act as reservoirs for infectious agents, potentially increasing exposure risk for wild salmon and other marine fish.
• The presence of pathogen eDNA suggests a link between aquaculture activities and pathogen distribution.
• Further research is needed to confirm if detected eDNA represents viable pathogens and to quantify risks to wild populations.