Effects of boulder addition on European grayling (Thymallus thymallus) in a channelized river in Sweden

Abstract

During the last century, the majority of Swedish rivers were heavily channelized to facilitate timber floating. This dramatically altered in-stream habitat by reducing the structural heterogeneity and increasing water velocity, which in turn had effects on the aquatic fauna. Today, extensive efforts to restore channelized rivers are being made by adding boulders to the streambed. In northern boreal rivers, evaluations of such restorations are often based on the response of trout and salmon populations. Few studies have investigated the effect on European grayling (Thymallus thymallus L), despite it being an important and vulnerable gamefish in both North America and Europe. This 6-year study investigated the effect of streambed restoration on grayling in a channelized, regulated (hydro-peaking) river in northern Sweden open to recreational fisheries. No effects on habitat preference, size, body condition, abundance or survival of grayling could be detected. The results are discussed based on grayling habitat preferences and behaviour, and give perspectives on streambed restoration in river conditions common to many Scandinavian grayling rivers today. The study is one of very few that presents multiyear abundance and survival estimates of grayling in a large boreal river.

Keywords:

• Grayling
• restoration
• abundance
• survival
• mark-resight
• timber floating
• streambed restoration

Acknowledgements

We thank Anders Bruks for valuable help in collecting the data.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Gustav Hellström

Gustav Hellström is an assistant professor in fish biology. He run the statistical analysis and wrote the mansuscript.

Daniel Palm

Daniel Palm is a fish biologist. He helped with the writing and analysis.

Tomas Brodin

Tomas Brodin is a professor in animal behavior. He helped with the writing and analysis.

Peter Rivinoja

Peter Rivinoja is a fish biologist. He helped with the writing and analysis.

Mikael Carlstein

Micael Carlstein is a fish biologist. He designed the study and collected the data.