Freshwater Pearl Mussel and its habitats (LIFE04/NAT/SE/00023)

Freshwater Pearl Mussel and its habitats (LIFE04/NAT/SE/00023)

• « Change Map size
• View in Google Earth

Key features of the case study

 Drivers

Main concerns: Ecological concerns Legal requirements: Natura 2000 Opportunities: Broader management plan (swedish national conservation plan)

95 % of the Fresh Pearl water mussel population in Central Europe has fallen. The specie is classified by IUCN as endangered and is included in the EU habitat directive. Sweden is home to a large part of the remaining population (a core area) and therefore have an international responsibility for the species’ long-term survival’.

 Pressures

Hydrological regime modification Artificial barries upstream from the site Artificial barries downstream from the site Alteration of instream habitats Sedimentation and sediment input Nutrients pollution Micropollutants Acidification

 Humans activities

Mainly forestry Agriculture

 Global objectives

Species enhancement and habitats improvement were the main objectives of the project by developing and testing methods to achieve a favourable conservation status for the freshwater pearl mussel (Margaritifera margaritifera) in Sweden. However, freshwater mussel was not the only target specie of the project. A freshwater mussel population decrease highlights a deterioration of the environnment, the improvement of freshwater mussels habitats will thus benefit other aquatic species such as host fish.

 Specific goals (process oriented)

In order to achieve the conservation of Margaritifera margaritifera, the project aimed to : 1. eliminate the migration obstacles to host fish along ten watercourses, 2. improve the river bed in eight watercourses, 3. manage the banks along two small rivers 4. Re-introduce young mussels (test in one stream)

 Measurable criteria

The mussel recruitment was expected within the coming 10–20 years. None measurable criteria were actually set in the frame of the LIFE project due its too short time frame. However, measurable criteria with regards to the Margaritifera margaritifera recruitment have been set in the frame of the swedish national conservation plan (XX).

Measures selection

Several measures were implemented aiming to restore the Margaritifera margaritifera population using different means:

- Water flow quantity improvement Repairing a dam that regulates the water flow into the stream Lillsjöbäcken to avoid water shortage in summer

- Sedimnt flow quantity improvement Blocking of 17 ditches with wood and ground materials to reduce negative impact from siltation

- Longitudinal connectivity improvement Removing obstacles Fixing incorrectly placed road culverts Building bypasses around migration obstacles

- In-channel structure and substrate improvement Deposit of gravel and small stones in fast-flowing river sectionsn (restoration of around 1 300 m2 of stream grounds across eight sites through )

- Riparian zone improvement Removal of spruce and other vegetation which impact on streams, in favour of deciduous trees along two shoreline sites (a total of 4.5 hectares buffer zone have been thinned and cleared along the streams Sollumsån and Bratteforsån)

- Specie enhancement Reintroduction of freshwater pearl mussels (1 000 mussels collected from a nearby watercourse in the same basin.)

 Constraints

Every measures were not implemented as foreseen due to different constraints. Some actions were actually compromised due to historic cultural values, and one action was postponed due to disagreement with landowner. Furthermore, the planned deposit of gravel was less than anticipated due to research which revealed lower need.

Ecological response

 Other biota

Due to the complex life cycle of the freshwater mussel, it will take 5-10 years (at least) before it is possible to assess the real conservation impact of the implemented actions. However, the first monitoring highlights an increase of freshwater pearl mussel larvae on the fish geals.

Monitoring before and after implementation of the project

 Before

Biotic, chemistry and hydromorphologic studies were carried before restoration in order to select suitable sites by evaluating the viability and the size of the population:

- BOTIC: Monitoring freshwater pearl mussel and host fish. Electricfishing were carried to evaluate the host fish population (and to assess mussel larvae parasites on fish geals) and mussels inventories were done by using an Aquascope or peep box (monitoring according to the standard method recommended by the Swedish Environmental Protection Agency)

- HYDROMORPHOLOGIC: Monitoring riverbed substrates by documenting the rate of sedimentation of riverbeds, the distribution of substrate size from silt to boulder, the turbidity of the water and the level of sedimentation (June-September)

-WATER QUALITY (especially pH)

 After

Those assessments were also carried after restoration. The post-monitoring, carried on by the County Administrative Board, still runs for the Margaritifera margaritifera population and also electric fishing. Besides, the University of Karlstad is currently monitoring the sedimentation of the river beds. Sedimentation samples were taken before and after the restoration to see whether the siltation/sedimentation has decreased. This monitoring aimed to evaluate the success and efficiency of the measures but also of the forest owners information (bad forestry management is common sources to sedimentation in streams).

 Reference site

Related Measures

• Remove barrier
• Narrow water courses
• Improve/Create water storage
• Reduce undesired sediment input
• Install fish pass/bypass/side channel for upstream migration
• Modify culverts, syphons, piped streams
• Develop riparian forest

Related Pressures

• Hydrological regime modification
• Artificial barriers upstream from the site
• Artificial barriers downstream from the site
• Alteration of instream habitat
• Sedimentation and sediment input