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Pacific salmon populations are declining due to a number of factors including climate change and pollution. Thus, it is crucial to monitor salmon populations in order to gain insights into their health and abundance. This information is essential for making informed decisions regarding conservation and management efforts.

However, the task of counting returning adult salmon is expensive, requires infrastructure (i.e. fish fences) that must span an entire water body and requires hours of daily human labor to physically count fish or operate sonar equipment.  These costs are currently a large barrier to salmon population counting. As a result, only a small portion of salmon runs are monitored and used for salmon stock assessment.

In this study, researchers from Simon Fraser University and the Gitanyow Fisheries Authority assessed the effectiveness of environmental DNA (eDNA) as a stock assessment tool for Pacific salmonids. The term “eDNA” refers to any trace fragment of DNA that is released by an organism into the environment (i.e., released into water, air or soil). For this project, the researchers quantified the eDNA released by salmon into the Kitwanga River and concurrently measured river velocity. These values were used to predict the number of salmon passing by the Kitwanga River Salmon Enumeration Facility daily during the salmon spawning season.

The eDNA predicted salmon counts for four Pacific salmon species (chinook, sockeye, coho and pink) were compared to the traditional human salmon counting method at the well-established Kitwanga River Salmon Enumeration Facility. The team showed that eDNA rates are predictive of human salmon counts for salmon species with large numbers of up-migrating (returning from the ocean and migrating up stream) adults (i.e. pink ~180,000). Ultimately, the research team found that eDNA is a reliable stock assessment tool for salmon runs with ~100 or more individuals migrating daily. 

Adopting eDNA for salmon enumeration may significantly impact both users and managers of BC salmon fisheries. This tool can enhance the efficiency of counting up-migrating salmonids, ultimately allowing more streams to be monitored.