Post-Spawning Survival and Downstream Passage of Landlocked Atlantic Salmon in a Regulated River

Repeat salmonid spawners may make large contributions to total recruitment and long term population stability. Despite their potential importance, relatively little is known about this life stage for anadromous populations and nothing has been reported for landlocked populations. Here, we studied post-spawning behavior and survival of landlocked Atlantic salmon in relation to downstream dam passage in the River Klarälven, Sweden. Eight hydropower stations separate the feeding grounds in Lake Vänern from the spawning grounds in the river, and no measures to facilitate downstream migration are present. Forty-nine percent of the salmon survived spawning and initiated downstream migration. Females and small fish had higher post-spawning survival than males and large fish. The post-spawners migrated downstream in autumn and spring and remained relatively inactive in the river during winter. Downstream migration speed in free-flowing river reaches was variable, averaging 9.30 km/day. Most fish passed the first hydropower station near the surface via upward-opening spill gates after a median delay of 25 min. However, no tagged fish successfully passed all eight hydropower stations to reach Lake Vänern. This result underscores the need for remedial measures to increase survival of downstream migrating kelts.