A novel automatic release cage increases survival of Atlantic salmon ( Salmo salar ) smolts released at night

Trap-and-transport of migratory fish is commonly used to bypass in-river obstructions. On the River Conon in Scotland, Atlantic salmon (Salmo salar) smolts are transported around two hydropower facilities. Smolt release occurs during daylight, when predation rates can be high. A novel automatic release cage (ARC) was designed to release smolts at night. Smolts were fitted with acoustic tags (n = 99) to compare survival. High post-release mortality was identified in the day-release group, with night-release survival >40% higher. ARCs can provide fishery managers with a cost-effective and reliable method of improving smolt survival.