A Preset Automated Device to Release Marked Juvenile Salmonids for Measuring Smolt Trap Efficiency

We describe a floating device designed for the automated release of marked groups of juvenile salmonids at a predetermined time upstream from smolt trap study sites.  This device is useful in studies using rotary smolt traps to estimate the number of downstream-migrating juvenile salmonids in streams and rivers.  The device assists in these projects by enabling the programmed release of fish at dusk when juvenile salmonids typically move downstream.  Release after sunset reduces predation, eliminating the loss of marked fish before they reach the trap site which can result in inflated estimates and lower calculated trap efficiencies.  This device also eliminates the need for project personnel to return to the study site at dusk to release the mark group.