Mörrumsån - Hemsjö

Mörrumsån - Hemsjö

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Key features of the case study

In the following section, background and motives of the restoration project which led to the initiation of the project are introduced.

Drivers and pressures

River Mörrumsån is an important reproduction site for Baltic salmon and sea trout. It has been estimated that smolt production in the river constitutes nearly 50 % of total smolt production in the rivers around the southern Baltic Sea. It is probably the most well-known salmon-bearing river in Sweden and sports fishing for salmon and trout in the river is internationally renowned. The river was exploited for hydropower production in the late 19th- and early 20th century which has created numerous migration barriers and reduced the available reproduction area for anadromous salmonid fish. Both upstream migration and downstream migration has been hampered since hydropower dams prevent fish from moving upstream and fish are often injured or killed in the turbines of the hydropower plants when moving downstream. Hemsjö is located ca. 20 km from the sea. There are two hydropower plants at the site ca. 3 km apart: Hemsjö övre hydropower plant and Hemsjö nedre hydropower plant. Hemsjö nedre hydropower dam used to be the first definite barrier in River Mörrumsån for salmon and sea trout migrating from the sea. Marieberg hydropower plant is located further downstream in the river but the hydropower dam was equipped with a functioning fish ladder (vertical slot fishway) in 1945.

The two hydropower plants at Hemsjö are connected through a river stretch with residual flow; the original natural river channel. Water flow in the natural channel used to be sporadic and irregular and no minimum flow was decided in the water rights agreement. The river stretch is furthermore affected by channelization, deepening and bolder removal from milling activities and timber floating. This has together with hydrological degradation led to deterioration of the bottom structure.

Global objectives

The restoration efforts at Hemsjö can be divided into two separate categories, (1) lateral connectivity and (2) habitat improvement.

1. The main goal of the first restoration project at Hemsjö carried out in 2003-2004 was to improve the potential for natural reproduction of Baltic salmon and sea trout in River Mörrumsån and to secure the population’s long term survival. Lateral connectivity should be restored at Hemsjö and the available reproduction area for anadromous salmonid fish in the river increased. This was also a goal of the IBSFC (International Baltic Sea Fishery Commission) Salmon Action Plan for the Baltic Sea. The restoration also served to increase fish production and to promote sports fishing in the river and the conservation of other species of the naturally occurring fish fauna was another important concern.

1. After the first restoration, which provided the natural channel between Hemsjö övre and Hemsjö nedre hydropower stations with an increased water flow, several habitat improvement projects have been undertaken in the river section. One habitat improvement project in 2004-2006 served to benefit especially the natural sea trout population in River Mörrumsån but also the salmon population. Another habitat improvement project in 2010 had the added incentive to indirectly benefit the fresh water pearl mussel (Margaritifera margaritifera) population. The glochidia larvae of the fresh water pearl mussel use salmon and trout as host fish in their life cycle. Habitat improvement was also carried out in the river section in 2012 within an EU LIFE+ project (UC4LIFE, LIFE10 NAT/SE/000046) with the broader goal to “strengthen the conservation status of the thick shelled river mussel (Unio crassus) and improve the ecological status of the rivers where it is found in Sweden”. Since host fish selectivity of the thick shelled river mussel glochidia larvae is poorly understood the goal of the restoration measures at Hemsjö was to create “natural conditions that favors diversity”.

Specific goals

1. (1) To restore lateral connectivity at Hemsjö fishways were to be constructed at Hemsjö övre and Hemsjö nedre hydropower dams; these should be constructed so that most naturally occurring fish species in the river could use them to migrate upstream. Water flow in the natural channel between the hydropower plants should furthermore be increased to enable fish migration. Hydropower production should also be reduced in the hydropower plants at Hemsjö övre, Hemsjö nedre and Marieberg in the spring when smolt migrate to the sea to minimize damage caused by the turbines and a nature reserve should be created in the area.

1. (2) The habitat improvement projects carried out in 2004-2006, 2010 and 2012 had the goal to improve and create new spawning grounds for salmonid fish in the natural channel between Hemsjö övre and Hemsjö nedre hydropower plants.

Related Measures

• Increase minimum flows
• Facilitate downstream migration
• Ensure minimum flows
• Install fish pass/bypass/side channel for upstream migration

Related Pressures

• Hydrological regime modification
• Discharge diversions and returns
• Artificial barriers downstream from the site
• Alteration of instream habitat
• Channelisation / cross section alteration