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. 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. 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.

Site description

No information found.

Measures selection

The following section introduces which measures were prepared, implemented and whether they were successful in reaching their related goals

Nature-like partial width (ca 5 m) rock ramps were constructed at Hemsjö övre and Hemsjö nedre hydropower dams in 2003-2004. Steel sheet piles were driven in to the river bottom to separate the ramps from the main channel. Water is allowed to flow over the partitioning and into the fishways at high flows. The fishways are ca 100 m and 60 m long, respectively.

A new water rights agreement for Hemsjö övre, Hemsjö nedre and Marieberg hydropower plants was established in the Swedish Environmental Court in 2003 (today replaced by the Swedish Land and Environmental Court). It stipulates among other things that: -A minimum flow of 1 m3/s should be directed through the fishways at Hemsjö övre and Hemsjö nedre hydropower dams and through the natural channel between 1 April and 15 November. During the remainder of the year a minimum flow of 0.5 m3/s should be directed through the fishways and the natural channel.

• During the salmon and trout spawning migration period, for 25 days between the dates 1 June and 15 November, 3 m3/s of water should be discharged through the natural channel between Hemsjö övre and Hemsjö nedre hydropower plants in addition to the dictated minimum flow.

• For a maximum of five weeks, between the dates 1 April and 15 June, hydropower generation in Hemsjö övre and Hemsjö nedre hydropower plants should be reduced to half the available potential at prevailing flow conditions.

• For a maximum of five weeks, between the dates 1 April and 15 June, hydropower generation in Marieberg hydropower plant should be completely halted.

A nature reserve (Mörrumsåns dalgång) that stretches from Hemsjö övre hydropower plant and 11 km downstream along the river was created in 2008. The nature reserve borders another nature reserve (Kärringahejan) in the upstream end. The in-stream habitats and diverse riparian zones in the nature reserve have been protected from exploitation.

In 2004-2006 ca. 100 m3 of salmonid spawning gravel (8-150 mm) was added with a crane lorry to ca. 15 different areas of the natural channel between Hemsjö övre and Hemsjö nedre hydropower plants that in other respects were deemed suitable for salmonid spawning and were accessible from the road. In 2010 ca. 100 m3 of salmonid spawning gravel (8-150 mm, and some 2-4 mm) was added with a helicopter to four additional areas that had not been visited in 2004-2006. In 2012 ca. 88 m3 of salmonid spawning gravel was added with a helicopter to two additional areas that had not been visited in 2004-2006 or 2010. In total ca. 20 gravel beds were created in the river section.

Success criteria

1. In general, success criteria for Swedish restoration projects are poorly developed and no such criteria for these restorations could be found.
2. In general, success criteria for Swedish restoration projects are poorly developed and no such criteria for these restorations could be found.

Ecological response

1. The creation of free migration routes at Hemsjö has opened up an additional 10 km of River Mörrumsån to spawning migrating anadromous salmonid fish. Results from the automatic fish counters in the fishways at Marieberg and at Hemsjö övre has revealed that in a given year on average ca. 50 % of the salmon and trout that pass through the fishway at Marieberg continue upstream through the fishway at Hemsjö övre. On average ca. 550 salmonid fish (range 293-954) are recorded in the fish counter at Hemsjö övre each year (2007-2013). Pike and other fish species have also been observed moving upstream through the fishways. In 2013 almost 2000 fishes other than salmon, trout, trout/salmon hybrids or rainbow trout were recorded moving upstream through the fishway at Hemsjö övre. Lateral connectivity has not been 100 % restored at Hemsjö however. Spawning migrating salmonid fish are reluctant to enter the fishway at Hemsjö nedre hydropower dam and continue upstream through the natural channel when flow is 1 m3/s (minimum flow during most of the summer and autumn according to the water rights agreement). Fish migration is thus halted downstream Hemsjö nedre hydropower plant. When an additional 3 m3/s of water is directed through the fishways and natural channel more fish enter the fishway at Hemsjö nedre and spawning migration is resumed.

The restoration has increased the area available for salmonid reproduction in River Mörrumsån by ca. 20 ha (equivalent to ca. 50 % of the total available habitat). Salmonid spawning was observed in the river section upstream Hemsjö already in 2004. Young salmon and trout have been caught by electrofishing in several sites upstream Hemsjö after the restoration, sometimes in very high densities (>2 individual/m2 for salmon and >1.3 individuals/m2 for trout). Mean densities for salmon in the river section (nine samplings at seven sites between 2010 and 2012) were 0.55 individuals/m2 and minimum densities recorded were 0 individuals/m2. The same numbers for trout were 0.69 individuals/m2 and 0.12 individuals/m2 respectively. Young salmon and sea trout have also been caught in the natural channel with increased flow between Hemsjö övre and Hemsjö nedre hydropower plants after the restoration (see below).

1. Salmonid spawning was observed in 2007 on all the spawning areas that were created in the natural channel between Hemsjö övre and Hemsjö nedre hydropower plants in 2004-2006. Electrofishing on the gravel beds that were created in 2004-2006 and 2010 have given salmon and trout catches of up to >0.8 individuals/m2. Mean densities for salmon (12 samplings at nine sites between 2010 and 2012) were 0.36 individuals/m2 and minimum densities recorded were 0.08 individuals/m2. The same numbers for trout were 0.14 individuals/m2 and 0 individuals/m2 respectively.

No fresh water pearl mussels were found in the areas where spawning gravel additions were made in 2010 before the restoration, a few duck mussels (Anodonta anatina) were found though. No mussels at all were found in the areas where spawning gravel additions were made in 2012 before the restoration. Because of the complex life cycle of the freshwater pearl mussel and the thick shelled river mussel, the mussels’ slow growth rate, and a likely poor supply of colonization sources within the river (at least for freshwater pearl mussel) any response in the mussel population to the restoration measures might lie far in the future. A response in the mussel populations to the restoration measures can furthermore be manifested anywhere in the river accessible to anadromous salmonid fish and not only in the 3 km stretch of the natural channel between Hemsjö övre and Hemsjö nedre hydropower plants.

Water quality response

1. The restoration was not expected to have any significant long term effect on water chemistry.
2. The restoration was not expected to have any significant long term effect on water chemistry.

Hydromorphological response

1. The construction of fishways and hydrological restoration measures at Hemsjö has increased lateral connectivity at the site and has opened up an additional 10 km of River Mörrumsån to migrating anadromous fish. Lateral connectivity has not been 100 % restored however since spawning migrating salmonid fish are reluctant to enter the fishway at Hemsjö nedre under minimum flow conditions (se precious section).

The diversion of more water through the natural channel between Hemsjö övre and Hemsjö nedre hydropower plants with an established minimum flow has created a permanent body of flowing water were there previously was a dry channel. The river stretch is still highly degraded however. Minimum flow in the river stretch established in the water rights agreement is 1 m3/s or 0.5 m3/s depending on the date. This should be compared with a natural mean annual flow of ca. 26 m3/s and a natural mean annual low flow of 8-9 m3/s. The flow regime is completely unnatural with a flow of 1 m3/s or 0.5 m3/s for long periods of time interrupted by sudden increases to 4 m3/s during the salmonid spawning migration period and to very high flows when excess water, or all the water, is discharged through the regulation dams.

1. The spawning gravel additions made in the natural channel between Hemsjö övre and Hemsjö nedre hydropower plants in 2004-2006, 2010 and 2012 have changed the bottom substrate composition in the river section somewhat. It is unclear whether this has restored the substrate composition to more natural conditions or not.

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