Using eDNA to Evaluate and Inform and Evaluate Fish Stocking Efforts

Stocking fish from Leadville National Fish Hatchery (Credit: Kayt Jonsson / USFWS via Flickr Public Domain)

eDNA sampling and analysis have been used to evaluate native fish populations for many years, and a 2023 article published in Scientific Reports highlights its utility in evaluating restocking and measuring stock improvements.

A key component of fishery management is evaluating current fish populations and the needs of the fishery. Ecosystem considerations like the preservation of key and endangered species, as well as the human factor in terms of recreational and commercial fishing, are essential components of any plan.

In cases where fishing demands are higher than what the native population can achieve (leading to total population declines from one season to the next), fish stocking is commonly conducted in order to “balance the books” of the fishery.

The Cost of Fish Stocking and Maximizing Efficiency

Depending on various factors, fish stocking can be a costly investment. As a result, fishery managers must constantly evaluate stocking strategies to help inform future approaches.

Stocked fish are purchased from hatcheries which price each fingerling (or older stock fish) per fish, which can become quite expensive in a larger fishery. Due to the price point, managers want to ensure that the stocked fish are reaching breeding age and contributing to the total population, not getting eaten by predators early on.

The age of the stocked fish and stocking location are both key considerations since water depth, and the presence of natural predators can result in a majority of stocked fish dying and, therefore, being ineffective. In determining ideal locations for stocking, eDNA can help identify where current populations reside.

Using eDNA to Assess Stocking Success

For years, eDNA has predominantly been highlighted as a means of establishing biomass and fish distribution in fisheries. However, more recent advancements have focused on unlocking the full potential of eDNA research and adding to existing management strategies.

More recent research shows that eDNA can be used to evaluate the success of stocking efforts. According to the Oregon Department of Fish and Wildlife, native and hatchery-reared fish may be the same species, but the eDNA of the two fish are different. As a result, eDNA can be used to evaluate if the stocked fish are surviving and still present in the environment well after the stocking event.

While there are other means of evaluating stocking success, limited funds and resources can make other strategies more challenging. The 2023 study found that eDNA sampling is a reliable, fast and accurate alternative method for measuring stock improvement.

Conclusion

eDNA sampling is non-invasive and doesn’t require any fish sampling or tagging. Though the use of tags and sampling can give a more complete view of the success of stocking, eDNA assessments can be effective under limited resources.