We are now at the beginning of the UN Decade on Ecosystem Restoration, in which the European Union has suggested an aim to restore tens of thousands of kilometers of European rivers. Atlantic salmon is one of the jewels of the European ecosystems, representing a species that has been culturally important for millennia and that is engrained in European life and economy. Large scale farming has in fact made it both widely available and one of the most visible fish on the planet. However, while salmon farming continues to expand, wild salmon is suffering throughout its range as habitats disappear and water quality declines. Restoration activities in the rivers that Atlantic salmon depend on for spawning and rearing as juveniles has therefore been widely adopted as a strategy to enhance production.
The latest Editor's Choice article in ICES Journal of Marine Science is the product of a December 2020 workshop held in Bergen, Norway at which experts from around the world were tasked with answering the question: what works for restoring Atlantic salmon populations? The subject was dominated by discussions about the role of hatchery production, the different challenges faced in different geographical regions, and the difficulty of identifying and resolving issues when the problem was difficult to identify. The authors' task evolved to address these questions, beginning with definitions of “success". They suggest that there are three levels of success, with the third level being a self-sustaining population with a harvestable surplus that can be targeted by fisheries. A standardized metric should be tracked in order to evaluate success, such as spawner counts or egg deposition. A review of the literature found a few examples of studies that had achieved this success, often by restoring water quality issues that were limiting production. The group agreed that hatcheries should always be of the gene bank type and the ultimate goal should be to end the hatchery production.
Ultimately, the authors concluded with five maxims that they agreed should guide restoration efforts for Atlantic salmon. Prevention is crucial to avoid the need for restoration, which means focusing on protecting populations and their habitat proactively before they decline below critical levels. When restoration takes place, scientists and management should engage locals and stakeholders to ensure efforts are relevant to local users, and then identify the problems needed to be addressed by restoration rather than defaulting to generic solutions. If there are enough resources, restoration can be successful but there are still mysteries that will cause tribulations to restoration programmes and patience is critical to ensure that a plotted course can be maintained.
This authors hope that their paper will provide insight to both scientists and managers on how restoration activities can progress, but they also anticipate that this topic will continue to evolve as new information emerges during this Restoration Decade.
