Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

Atlantic salmon smolt migration in a regulated river: anthropogenic vs natural influences (#178)

Andrew Harbicht 1 , Olle Calles 1
  1. Karlstad Universitet, Karlstad, Värmland, Sweden

Dams and barriers to migration are commonly cited causes of mortality among downstream migrating salmonid smolt due to the delays and physical damage that passing such barriers can cause. But the environmental and ecological influences of impoundments are not limited to their immediate environment. Changes to the morphology and hydrodynamics of a river can occur over extended stretches of a regulated river, both upstream and downstream from a hydroelectric dam. For this reason, it is important to understand how smolt movement and mortality is affected by the entire range of environmental and ecological conditions that they experience along their migratory route. As part of a multi-year dam removal study, radio-telemetry was used to monitor the downstream migration of Atlantic salmon smolt in the Mörrumsån, a regulated river in Sweden. Using time-to-event analyses, the impacts of natural and anthropogenic factors on migratory dynamics were assessed for altered and unaltered sections of the river, including sections expected to be most strongly affected by the future dam removal. With Sweden being among the countries with the highest number of regulated rivers in the world, and new governmental regulations making the future of many dams uncertain, furthering our understanding of which factors affect the riverine portion of a fish's migration is crucial to help industry and government make sound, informed decisions.