Johan Östergren

Forecasting Environmental Responses to Restoration of Rivers Used as Log Floatways: An Interdisciplinary Challenge

Log floating in the 19th to mid 20th centuries has profoundly changed the environmental conditions in many northern river systems of the world. Regulation of flow by dams, straightening and narrowing of channels by various piers and wing dams, and homogenization of bed structure are some of the major impacts. As a result, the conditions for many riverine organisms have been altered. Removing physical constructions and returning boulders to the channels can potentially restore conditions for these organisms. Here we describe the history of log driving, review its impact on physical and biological conditions and processes, and predict the responses to restoration. Reviewing the literature on comparable restoration efforts and building upon this knowledge, using boreal Swedish rivers as an example, we address the last point. We hypothesize that restoration measures will make rivers wider and more sinuous, and provide rougher bottoms, thus improving land-water interactions and increasing the retention capacity of water, sediment, organic matter and nutrients. The geomorphic and hydraulic/hydrologic alterations are supposed to favor production, diversity, migration and reproduction of riparian and aquatic organisms. The response rates are likely to vary according to the types of processes and organisms. Some habitat components, such as beds of very large boulders and bedrock outcrops, and availability of sediment and large woody debris are believed to be extremely difficult to restore. Monitoring and evaluation at several scales are needed to test our predictions.

Linking genetic assignment tests with telemetry enhances understanding of spawning migration and homing in sea trout Salmo trutta L.

Telemetric and molecular techniques are powerful tools for investigating patterns of species dispersal, habitat use, and reproductive behavior. Yet, these methods are rarely combined when studying spatial structures of migrating animals. This study combines migration data with genetic assignment tests of radio-tagged sea trout, Salmo trutta L., in two Swedish rivers. We investigate how the genetic information enhances the interpretation of the telemetry data. Individual gene frequencies of tagged fish are assigned to baseline samples of brown trout collected in tributaries and the main stems. The genetic assignment tests confirm that individuals returned from the sea to their natal stream, but also suggest that some individuals migrated to other than their native habitat. In total, 82% (R. Piteälven) and 37% (R. Vindelälven) of fish that were successfully assigned to a sample in a baseline migrated to an area in the vicinity of the sample location. The difference between rivers is likely due to low genetic differentiation among baseline samples and effects of stocking of fish in the R. Vindelälven. Combining the two techniques enhances understanding of migration behavior, important for conservation and management.

Monitoring Juvenile Atlantic Salmon and Sea Trout in the River Sävarån, Northern Sweden

Downstream migrations of Atlantic salmon (Salmo salar) and sea trout (S. trutta) smolts were monitored in the in northern Sweden to evaluate the river’s potential as a national index river for salmonid populations in the Baltic region, and to acquire information for stock conservation plans. A rotary screw trap was installed and operated from 2005 to 2008. Recapture rates of tagged smolts were high (from 8% to 31%), which allowed smolt abundances to be estimated. Between 2,600 and 3,900 salmon and 500–1,500 trout emigrated from the river each year. Genetic analyses made it possible to identify the origin of salmon and trout smolts and to determine whether they originated from the Savaran stock or from stocks in neighbouring rivers. In 2005 and 2006, most of the salmon were from the Savaran stock, which previously had been thought to be extinct. By contrast, 58% and 52% of the salmon analysed in 2007 and 2008, respectively, originated from stocks other than Savaran. The density of salmon and trout 0+ parr (i.e. recruitment success) based on electro-fishing was a poor predictor of smolt abundance 2 to 3 years later. The smolt trap data combined with genetic analyses provided valuable information to develop stock conservation plans.