Fish forensics: environmental DNA detection of juvenile coho salmon and resident salmonids in Pacific coastal streams




MacAdams, Jeffrey

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Conventional fish monitoring requires considerable investments of equipment and labour, and often harmful and potentially fatal techniques. Emerging methods allow detection of aquatic animals by collecting water and extracting DNA that has been shed to the environment (eDNA). Present knowledge gaps in the field include minimum densities necessary for consistent detection, and persistence of eDNA after a target species has left a site. I conducted three experiments at a salmon hatchery in British Columbia to address these knowledge gaps. Water samples were taken from flow-through tanks with juvenile Coho Salmon densities ranging from 38.0g/1000L to 0.6g/1000L. To simulate field surveys in recently abandoned habitats, I sampled water from tanks after removing fish, at flow-through volumes ranging from 20,000L to 1,000,000L. Post removal sampling occurred starting at one hour and ending after just over four days of flow-through time. Water samples from tanks containing one or more fish tested positive for Coho DNA at least 70% of the time, increasing at higher densities. Samples taken after removing the fish had detection probability of 75% at flow-through volume of 40,000L. Detection failed at flow-through volumes greater than 80,000L. In stream samples, all sites with Coho or salmonid presence confirmed by conventional trapping also tested positive for target species’ eDNA. Two sites tested positive for Coho eDNA where conventional methods failed, indicating a possible higher sensitivity of eDNA sampling. I also mapped the distribution of juvenile Coho Salmon through multiple tributaries of a productive salmon system with conventional and eDNA detections. This study improves on an emerging method with a new species by addressing existing uncertainties regarding eDNA detection threshold, and signal persistence through dilution in a simulated stream pool habitat. It also demonstrates that eDNA methods can be used to assess coastal streams for presence of juvenile and resident salmonid fishes.



environmental DNA, Coho Salmon, non-invasive detection, salmonid fish