Migration of Yearling Sockeye Salmon (Oncorhynchus nerka) as Determined by Time-Lapse Photography of Sonar Observations

Abstract

The seaward migration of sockeye salmon smolts through the Babine Lake system to its outlet was examined by taking film records of the Plan-Position-Indicator display of a high-frequency sonar whereby each frame of film was exposed during one scan of the sonar unit. Frame-by-frame analysis of the films revealed information on speed, direction, and diurnal timing of migration of sockeye smolts during a 24-hr period.Migratory activity in the lake centered around dusk and dawn, a similar pattern to that near the outlet for smolts entering the river on their way to sea.Speeds of movements were 19–51 cm/sec (mean 30 cm/sec). Greatest velocities occurred at dusk and dawn. They were close to the maximum sustained swimming speeds determined under laboratory conditions for sockeye smolts of the same size and within similar temperature ranges as in the field.The most direct movements of targets were found at twilight, when migration activity was highest. In general, directional tendencies were consistent with the shortest route to the outlet. In some observations near the junction of Main Lake and Morrison and North arms, movements were observed which would lead the smolts away from the outlet. Consequences of such movements are discussed and compared with data from tagging operations.