Documented impacts of barriers and wetlands on salmonids and how to solve problems

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1 Documented impacts of barriers and wetlands on salmonids and how to solve problems Jan Nielsen Technical University of Denmark Section for Freshwater Fisheries and Ecology

2 Denmark is a lowland Bornholm Highest point: 171 m above sea level No natural barriers in the streams (except on Bornholm) More than 90 % of the streams are regulated

3 Many fish species migrates between streams and the sea High population densities and growth rates of salmonids

4 Most Danish streams are small < 2,5 m s wide Stream length (km) Mean stream width (m)

5 Some river spawning species North Sea houting (Coregonus oxyrhynchus) Sea- trout (Salmo trutta trutta) River lamprey (Lampetra fluviatilis) Dace (Leuciscus leuciscus ) Grayling (Thymallus thymallus) Salmon (Salmo salar)

6 Salmonids, lampreys and some other fish spawn on riffles in the gravel of the stream, where also clean-water invertebrates are found.

7 Spent Salmon from River Skjern make very long migrations as far away as Svalbard Svalbard River Skjern

8 Number of spawners Populations of salmon and trout are increasing Spawning run of Salmon to River Skjern

9 Brown trout yearlings from spawning Colours indicate the ecological status according to the Waterframe Directive and the Danish Trout Index DFFVø Brooks < 2m Numbers/100 m 2 Streams >= 2m Numbers/100 m > 130 (high status) (good status) > 250 (high status) (good status)

10 Good or high ecological status in 29 % of the trout streams according to the Danish Trout Index DFFVø

11 Anglers harvest a big seatrout for every 4-6 meters of trout streams with healthy populations - each year. 85 % of the seatrout are caught in salt water.

12 THE LIFE CYCLE of salmon and sea trout - avoid «bottlenecks» Spawning migration Migration Sea residence Spawning Hatching Downstream migration

13 Spawning and rearing areas

14 Natural slope is the key to succesfull restoration Further, gravel composition and low water is important Natural riffle with a self-sustaining trout population

15 Recommended spawning gravel size based on natural composition Diameter mm mm Small streams (< 3 m) Larger streams and rivers (> 3 m) 85 % 15 % 75 % 25 %

16 Local involvement in restoration of spawning areas

17 71 habitat improving projects Density of juvenile brown trout almost tripled after restoration

18 Man made bypass stream with spawning areas 1991 Now allways high ecological status (1,3 yearlings/m2) High ecological status

19 Remeandering of River Vejle at Vingsted

20 How to avoid losses of migrating fish?

21 Many problems at culverts

22 If removal of the culvert is impossible Water level in the culvert and improvement of upstream passage may be raised by establishment of spawning areas Culvert Water level raised 15 cm Spawning area

23 Effects of weirs Barriers for fish migrations (up- and downstream direction) Destruction of natural spawning and nursery areas in the flooded zone Flooded zone 2008

24 Heavy losses of up- and downstream migrating fish at weirs Water Mill Fish farming Hydropower

25 Dams, weirs and lakes can be deadly for downstream migrating fish Type Average % smolt-loss Mill ponds 30 Traditional fish farms 42 Hydropower stations 82

26 Reestablishment of a brown trout population - the natural solution ,5 km of flooded zone The River Gudenå was reestablished In the flooded zone

27 Now allways high ecological status for brown trout on the natural spawning areas 1,5 km upstream the weir High ecological status

28 Also a large increase of the trout population downstream the weir High ecological status

29 Smolt (Oxford Dic): A young salmon (or trout) after the parr stage, when it becomes silvery and migrates to the sea for the first time

30 6 mm grids necessary to stop smolts

31 Migrating fish follow the water They often fail to find small fish passages Main flow Main flow Small fish ladder Small bypass stream

32 River Kongeaa Fish Farm No smolt loss after reconstruction to a modern fish farm (decreased water intake, removal of weir) Year Smolt loss (%)

33 Barriers for the spawning run of salmon and trout at weirs and small fish ladders Video: Bo Skelmose and Jørn Chemnitz

34 After removal of the weir (still water intake to fish farm, 1 mm grid) Removed weir Fish farm

35 Now the salmon population in River Varde is increasing

36 Improvement of the sea trout population in River Villestrup Spring: 22 meters over sea level Length: 20 kilometers Villestrup Gods

37 River Villestrup 1999: 7 fish farms Very few seatrout Fish Farm River Malfunctioning fish ladder

38 Significant increase of smolt numbers following removal of the 7 weirs at fish farms in Yearly run of sea trout smolts Year Data: DTU Aqua and Thorsten Møller Olesen

39 Stream length: 14 km 250 seatrout/km or 1 seatrout/4 m

40 Still many man made barriers in Denmark The waterplans point out a number of problems to be solved

41 Wetlands Often established at streams with the purpose of removing nutrients from the water

42 River Omme: Increasing population of salmon, trout and grayling The wetland was established as a remeandered river with spawning riffles and periodic natural flooding of the valley River Omme

43 Wetland at River Von: Increasing populations of salmon and trout Remeandered river with spawning riffles and periodic natural flooding River Von

44 Lakes Delays, loss of orientation and high mortality of migrating smolts

45 Establishment of wetlands as lakes directly in rivers can introduce heavy losses of smolts

46 Egå Engsø established as a wetland in October 2006 Spring 2005 and 2006 No loss of smolts Now 74 % smolt loss (8 years of monitoring since 2007) Data from Schwinn (2016)

47 Smolt loss is % in Årslev Engsø - etablished as a wetland in 2003 River Aarhus

48 Smolts can survive if a lake is separated from the river with limited water intake to the lake River Vejle wetland at Skibet (established 2004) Only 19 smolts (0,1 %) moved into the lake in 2005 Main river flow Limited water intake to the lake 26 ha lake Inlet Outlet Vejle Å flows south of the dike. (Only 8 % of mean min flow goes through the lake = 230l) Data from Vejle Kommune and Vejle Amt

49 Conclusions Fauna passage improvement projects for riverine species The best projects involves natural solutions: When the dam, weir or road culvert are completely removed and the watercourse restored to the original gradient and flow without diversion of water from the river. Heavy losses of migrating riverine species can be expected if the fish have to pass lakes.