An Overview of Kelt Migration in Regulated Rivers: Status, Knowledge Gaps, and Future Directions Toward Safe Downstream Passage at Hydropower Facilities

Atlantic salmon (Salmo salar), brown trout (Salmo trutta), and steelhead trout (Oncorhynchus mykiss) kelts have important conservation value for population resilience. Nonetheless, relative to other salmonid life-stages, knowledge on their behavior and survival is poor. This is especially true for kelt downstream migration in rivers fragmented by hydropower plants (HPP), even though the physiological and survival consequences are severe when functional connectivity is not provided. Here, the existing information about kelt downstream migration past HPP was summarized, beginning with an overview of iteroparous salmonid lifecycles. Then, the importance of kelts for conservation and the threats they encounter while migrating was discussed. Finally, the current corpus of peer-reviewed literature and reports focused on kelt migration in these systems was presented. Kelt studies have focused on five main themes: (1) postspawning survival, (2) migration delays before dam passage, (3) passage selection and guidance efficiency, (4) passage mortality, and (5) the swimming behaviors of kelts during migration. Overall, there was a paucity of information about kelts and several information gaps and needs for future research. This work should inform scientists and river managers on the conservation of salmonids in regulated rivers, including the development of passage solutions for safe downstream migration.