Swedish Agency for Marine and Water Management

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Åtgärdsprogram för flodpärlmussla: Margaritifera margaritifera (Linnaeus, 1758)
Natur och Människa AB.
Perfomers of environmental monitoring, The County Administrative Boards, The County Administrative Board of Västernorrland.
Responsible organisation
2020 (Swedish)Report (Other academic)
Abstract [sv]

Flodpärlmusslan, Margaritifera margaritifera (Linnaeus, 1758) är en av Sveriges sju inhemska sötvattenslevande stormusslor. Arten har påträffats i 637 vattendrag, i landets alla biogeografiska regioner, från små bäckar till stora älvar. Den lever nedgrävd och har höga krav på sin miljö. Vattnet ska vara klart, syrerikt, näringsfattigt och pH-värdet ska vara minst 6,2. Flodpärlmusslan är beroende av öring eller lax som värddjur under larvstadiet.

Flodpärlmusslan har försvunnit från drygt en tredjedel av de vattendrag där den fanns i början av 1900-talet. Föryngring sker endast i ungefär en tredjedel av de vattendrag där den fortfarande finns kvar, dock med stora regionala skillnader

Arten har gått tillbaka på grund av bland annat långsiktigt försämrad vattenkvalitet, försämrat habitat och minskad värdfiskpopulation. Vattenkraftsutbyggnad, andra vattenregleringar och föroreningar har påverkat populationerna kraftigt i södra och mellersta Sverige under de senaste hundra åren.

I åtgärdsprogrammet listas bland annat följande åtgärder:

  • Alla uppgifter om förekomst ska läggas in i nationell datavärd (Musselportalen) för att utgöra underlag för framtagande av digitala kartskikt.
  • Samtliga markägare med förekomst av flodpärlmussla ska informeras. Som hjälp ska en reviderad broschyr om musslan tas fram.
  • Inga vandringshinder ska skapas i samband med ny- och ombyggnad samt reinvestering av vägar och järnvägar.
  • Ny kunskap ska tillföras genom nationell genetisk screening och utredning om öring och/eller lax är värdfisk i större vattendrag.
  • Minst två nya flodpärlmusselvatten per län ska skyddas och minst fyra flodpärlmusselvatten per län ska restaureras.
  • Åtgärdsbehovet ska utredas för minst hälften av länens populationer.
  • Skötselplaner för naturreservat ska revideras så att flodpärlmusslans krav tillgodoses.
  • Artificiell förökning bör initieras i prioriterade vattendrag.
  • Uppföljningen ska stärkas och genomförda åtgärder ska sammanställas för att kunna dra nytta av gjorda insatser.
  • Erfarenhetsutbyte i form av seminarier och en internationell konferens ska genomföras.
Abstract [en]

The Freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758) is found in 646 streams spread all over Sweden. The total number of mussel specimen is estimated to at least 40 million. Sweden holds most of the approximately 1,600 populations known in Europe. Together with Norway and Finland, Sweden accommodates around three quarters of all populations, hence the region is a stronghold for the species 

The Freshwater pearl mussel has a parasitic larval stage on the gills of Brown trout Salmo trutta, the main host fish in Sweden. There is an enormous loss in all stages of the reproduction cycle. A one-hundred-yearold mussel is estimated to produce only 3.2 young mussels.

Freshwater pearl mussel is amongst the most long-lived species on Earth. The oldest specimen found in northernmost Sweden was more than 280 years old. Normally the life span in Scandinavia is 100-250 years.  Freshwater pearl mussel needs good water quality, clean bottom substrate and suitable host fish. In Sweden, recruiting populations are only found in streams with pH>6.2, total phosphorus <8 µg/l, nitrate <125 µg/l, turbidity <1 FNU, colour <80 mg Pt/l, fine inorganic particles <25%, redox potential >300 mV, density of young Brown trout ≥5/100 m2. 

Given the species’ environmental requirements it is an important indicator and umbrella species. The Freshwater pearl mussel is also a suitable flagship species for nature conservation activities connected to running waters.

In Europe, the number of populations has decreased by 80% since 1920. In Sweden, we observe an ongoing decline among the Freshwater pearl mussel populations shown by lower recruitment and decreased abundance. Approximately half of the remaining populations lack recruitment. Therefore, the species is nationally red-listed as Endangered (EN). 

The main reason for the decline is changes in land use causing physical and chemical changes of the streams. Most serious is siltation of streambeds, which causes mortality in juvenile mussels. As most of the Swedish mussel streams are situated in forest landscape, forest management is of crucial importance. Stream acidification caused by airborne pollutants earlier caused mussel death in large areas. Pearl fishing is forbidden by law since 1994, and is at present not regarded as a problem. 

The first Swedish action plan for Freshwater pearl mussel was published in 1991 and revised in 2005, resulting in legal protection of a number of important mussel waters, habitat restoration, re-introduction, artificial recruitment and liming of acidified steams. There are also monitoring programmes at national and regional levels.

In Sweden, the regional authorities, the County Administrative Boards, have a key role in conservation. There are 16 counties with Freshwater pearl mussel streams. 

Proposed actions: 

  • Incorporation of all data on occurrence into the national mussel database. Production of up-dateddigital map layers. 
  • Information activities aimed at landowners and the public, including publishing of a new information brochure.  
  • Focus on eliminating migration barriers when constructing or reconstructing new roads and railways.  
  • National genetic screening of Freshwater pearl mussel, and a survey on whether Brown trout or Atlantic salmon are the host fish in large rivers.  
  • Inventories of the main channel of large rivers with potential occurrence of Freshwater pearl mussel.  
  • Legal protection of two new localities in each county and habitat restoration of four mussel habitats per county.  
  • Revision of nature reserve’s management plans in order to include actions for the Freshwater pearl mussel.  
  • Artificial recruitment is initiated in prioritized waters.  
  • Follow-up studies of actions and compilation of the results. 

The cost for conservation measures recommended by this action plan is estimated at 216 471 000 SEK during 2020-2024.

Place, publisher, year, edition, pages
Göteborg: Havs- och vattenmyndigheten, 2020. , p. 100
Series
Swedish Agency for Marine and Water Management report ; 2020:19
Keywords [en]
Freshwater pearl mussel, umbrella species, flagship species, siltation, migration barriers, artificial recruitment
Keywords [sv]
Flodpärlmussla, Margaritifera margaritifera, åtgärdsprogram, paraplyart, flaggskeppsart, sötvatten, vattendrag, rödlistad, digitala kartskikt, vandringshinder, artificiell förökning
National Category
Environmental Sciences
Research subject
Finance, National; Guidances, Instructions, Methods, Methods of Environmental Monitoring; Environmental Objectives, A Rich Diversity of Plant and Animal Life; Environmental Objectives, Flourishing Lakes and Streams
Identifiers
URN: urn:nbn:se:havochvatten:diva-260ISBN: 978-91-88727-83-1 (electronic)OAI: oai:DiVA.org:havochvatten-260DiVA, id: diva2:1438910
Available from: 2020-06-11 Created: 2020-06-11 Last updated: 2022-07-18

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