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Exorbitant mortality of hatchery-reared Atlantic salmon smolts Salmo salar L., in the Meuse river system in the Netherlands


Stocking Atlantic salmon Salmo salar L. in the Meuse river system is unsuccessful, since hardly any adults return upstream. To investigate problems during seaward migration, individual salmon smolts were tracked in the Dutch part of the river Meuse, using the Nedap Trail® system. The study included a comparison for two seasons, one with high (2010) and one with low (2011) discharge conditions. Cultivated smolts (Loire-Allier strain, n = 100 per year) were implanted with telemetry tags and released in the tributary Roer in March, at the beginning of the natural smolt run. The study area was split into four river sections each characterized by different conditions: tributary Roer, main river Meuse extensively dammed, main river Meuse free flowing and the estuary. Mortalities differed considerably between sections. In the free flowing river Meuse the mortalities were relatively low (10 and 25 %). Mortalities were high in the tributary (44 and 45 %), the dammed river (46 and 49 %) and in the estuary (89 and 90 %). Only 2 and 3 % of the smolts escaped into the North Sea. Results are discussed in relation to environmental factors light and discharge and the presence of man-made obstacles: weirs, hydropower plants and a sea lock. A lack of current and delays at man-made obstacles result in disorientation of fish, a higher risk of predation and disturbance of the smolt run timing. Mortality causes must decrease for sustaining a salmon population in the Meuse.

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  1. The water discharge in the Dutch Meuse river system is regulated with seven main weir-sluice complexes, of which two include hydropower plants. These complexes are named after neighbouring towns, from sea onwards these are called: Lith (hydropower, 14 MW), Grave, Sambeek, Belfeld, Roermond, Linne (hydropower, 11,5 MW) and Borgharen. Smolts in this study had to pass all barriers, except Linne and Borgharen.

  2. Rhine, 2200 m3/s annual mean discharge at Lobith; Meuse, 230 m3/s annual mean discharge at Borgharen. The watershed area of the Meuse river basin covers an area of approximately 35.000 km2, divided amongst (km2): France (9000), Luxemburg (less than 500), Belgium (14000), Germany (4000) and the Netherlands (8000). The tributary Roer (in German: Rur) has a total length of 165 km, of which 21.5 km is located in the Netherlands (width = 10–22 m). The watershed area of the Roer measures 2340 km2, which is 7 % of the watershed area of the Meuse; the slope of the river is 643 m from source to entering the Meuse.

  3. Eggs and parr are being stocked in the Roer each year, upstream in Germany. The average weight of a random 100 smolts in 2010 was 34 g, with lengths varying in-between 13 and 20 cm (Gubbels et al. 2012). Smolt size increases with age and smolt length is flexibly dependent on growth rate (Økland et al. 1993). In nature, smolt size and age varies widely among populations (Klemetsen et al. 2003).

  4. The main stream of tributary Roer is directed into a hydropower plant, located in the town Roermond (max 250 kW, called “Elektro Chemische Industrie, ECI”). Near the entrance an extra Nedap station (Nr.02) was installed for this study. A smaller stream, called Hambeek offers a detour into the Meuse, but here no Nedap station is installed. In 2008 the hydropower plant was equipped with a fish guidance system. It is assumed that with this system installed, a save passage of smolts is ensured. Water is directed via a wedge wire screen into the turbines, which consists of a trash rack with mesh apertures (1 cm between bars). In front of the trash rack, smolts can choose between three diversions: 1) the smolts trap, 2) the eel bypass and 3) the fish ladder. Test fish not detected at Nr.02 or caught in the smolt trap, could have swam into the Meuse through either the Hambeek, the eel passage or the fish ladder. These fish can be detected at station Nr.04 in the Meuse.

  5. The sea lock consists of 17 discharge sluices, each equipped with two sluice doors: one on the river side and the other on the sea side. The doors at the river side are kept open under all circumstances. Depending on the discharge, one or more seaward sluices are being opened gradually.


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The authors would like to thank these organisations for their support: The Interreg IVB North Sea Region Programme Living North Sea, the World Wide Fund (WWF), the Dutch Ministry of Transport, Public Works and Water Management (RWS), Lachs und Meerforellen Sozietät, Visserij Beheer Commissie Roerdal, Water authority Roer and Overmaas, Stiftung Wasserlauf, stiftung fur Gewasserschutz & Wanderfische NRW, The regional angling organisations Limburg and South-West Netherlands, and the Dutch fly-fishing organisation (VNV). Jaap Quak, Sportvisserij Nederland, helped with literature. Remko Verspuij, Sportvisserij Nederland, helped with statistical calculations.

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Correspondence to Niels Brevé.

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Brevé, N., Vis, H., Spierts, I. et al. Exorbitant mortality of hatchery-reared Atlantic salmon smolts Salmo salar L., in the Meuse river system in the Netherlands. J Coast Conserv 18, 97–109 (2014).

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  • Atlantic salmon
  • Salmo salar L.
  • Smolt mortality
  • Downstream migration
  • River Meuse
  • Nedap Trail® system