University of Massachusetts Amherst ScholarWorks@UMass Amherst International Conference on Engineering and Ecohydrology for Fish Passage International Conference on Engineering and Ecohydrology for Fish Passage 2017 Jun 19th, 4:10 PM - 4:30 PM Loss of smolts in reservoirs and the effects of barrier removal in lowland rivers Niels Jepsen DTU Aqua Follow this and additional works at: http://scholarworks.umass.edu/fishpassage_conference Jepsen, Niels, "Loss of smolts in reservoirs and the effects of barrier removal in lowland rivers" (2017). International Conference on Engineering and Ecohydrology for Fish Passage. 5. http://scholarworks.umass.edu/fishpassage_conference/2017/june19/5 This Event is brought to you for free and open access by the Fish Passage Community at UMass Amherst at ScholarWorks@UMass Amherst. It has been accepted for inclusion in International Conference on Engineering and Ecohydrology for Fish Passage by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact scholarworks@library.umass.edu.
Loss of smolts in reservoirs and the effects of barrier removal in lowland rivers Corvallis-2017 Niels Jepsen, DTU Aqua
1. Indirecteffects of dams 2. Resultsfrom reservoirs and wetlands/ponds 3. Why aresmolts so vulnerable? 4. Barrier removal in Denmark and river restoration 5. Effects and documentation
Focus mainly on upstream passage, later downstream, but indirect effects may be more important
Physicalinjury Delay(leadingto-) Increasedpredation Loss of habitat Temperature, ph, etc.
Hydropower effect on smolts
ALS Hydro-plant Dam Ans Bridge Salmon & Trout ALS Unknown (21) Passed (5) Kongensbro ALS Stayed in lake (4) Eaten (44) Smolttrap Release site Jepsen et al 1998
Reason for increased mortality: Predation
Also a downstream problem 21/27 = 78 % were predated within the first 4 km Koed et al 2002
River Reservior/Lake 50 N=8 Smolt loss km -1 (%) 40 30 20 10 0 N=8 Trout N=10 N=4 Salmon
Problems at weirs for downstream migrating fish Obstacle Mean smolt loss (%) Water mills (n=5) 30 Fish farms (n=38) 42 Hydropower stations (n=7) 82 Aarestrup et al 2006
Loss is cumulative! Number of surviving fish Mill ponds Fish farms Reservoir's Number of weirs
Establishment (restoration) of wetlands in lower rivers cause great problems for the fish. Year Smolt-loss (trout) 2005 0 2006 0 2007 71 2009 81
Results 2016 Of 74 tagged salmon, 8 were lost in the river (4 from pike, 4 from birds). Of the remaining 66, 17 were found in cormorant colonies.
Smoltloss in wetlands - trout Year Wild Hatchery Success Wild Success Hatchery 2009 959 / 19 % / 2010 441 / 23 % / 2011 414 498 13 % 25% 2012 548 499 39 % 21 % 2013 968 500 26 % 21 % 2014 462 427 25 % 18 % 2015 1491 483 33 % 22 % Total/mean 5283 2407 26 % 22 %
Where are the smolts vulnerable? Transition from lotic to lentic water Impoundments (lakes, reservoir) Estuaries Coast Obstacles (dams, weirs, barrage) Why?
Gradient is important in lowland rivers Height above sea-level Weir A Water surface Floodedzone downstream migrants rheophillicfish habitat Stream bed Weir B Distance from source Aarestrup et al 2006b
100 90 80 70 60 50 40 30 20 10 0 40 Elavation lost to weirs (%) = habitat lost? 24 Villestrup (22 m) Omme (75 m) Mølleåen (20 m) Gudenaa (69 m) 75 36 Birnie-Gauvin et al. 2017
1. Loss upstream barriers 2. Loss downstream barriers 3. Loss of habitat Can these problems be mitigated? Yes, by breaching the dams
Effects of dam removal 700 Number of salmon caught 600 500 400 300 200 100 0 2000 1990 1980 1970 1960 1950 1940 1930 1920 1910 1900 1890 Annual catches of Salmon in the estuary of River Skjern, 1900-1978 Otterstrøm(1938) and Statistic yearbooks, the Ministeryof Fisheries
Genetic studies 4 indigenous populations left in 1999! River Storå River Gudenå River Skjern River Varde River Kongeå Sneum River Ribe Å River Brede River Vidå Nielsen, Hansen & Bach (2001)
Number of salmon caught Annual run size app. 12,000, anglers catch 40 %, but keep only 10. High proportion of MSV, mean size 78 cm. Most are wild.
Fishing possibilities for the public The value of recreational fishing in DK is 450 mio $/year In the local area of Skjern Salmon alone generates 2 mio $
Successful restoration of salmon populations is based on knowledge obtained from research and monitoring 3500 Salmon spawning-run - River Skjern 3000 2500 2000 1500 Restoration of habitat/removal of weirs 1000 500 0 1901 1906 1911 1916 1921 1926 1931 1936 1941 Cormorant culling programme in the estuary 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006 Supportive breeding procedure optimised Restrictive regulation of the Fishery -Estuary: no-take zone -Restrictive regulation of the commercial fishery -River: restricted period, catch limit, C&R
Denmark is a lowland Bornholm Highest point: 171 m above sea level No natural barriers in the streams More than 90 % of the streams are regulated
Measures Introduce substrate
Measures Removal of underground streams
Measures
Examples:Upper Gudenå
Skjern å 1999
Skjern å 2002
Remeandering of River Vejle at Vingsted 2013 2015
Denmark world champion in river restoration?? Number of restoration projects Costs (million DKK)
71 habitat restoration projects Density of juvenile brown trout almost tripled after restoration
Measures Removal of obstacles
One way to restorea stretchafterremoval of a small dam Naturligt Build up with rocks Then pack it up with pebbles Result: stream with variation
Local involvement
Still barriers in DK? The waterplans point out a number to be dealt with
Man made bypass stream with spawning areas 1991 Now allways high ecological status (1,3 yearlings/m 2 ) High ecological status
Reestablishment of a brown trout population - the natural solution 2008 2008 1.5 km of inundated zone The River was reestablished
Now high density of brown trout on the natural spawning areas 1.5 km upstream the weir
Also a large increase of the trout population downstream the weir High ecological status
Improvement of the sea trout population in River Villestru Spring: 22 meters over sea level Length: 20 kilometers Villestrup Gods
River Villestrup 1999: 7 fish farms Very few seatrout Fish Farm River Malfunctioning fish ladder
Smolt counts following removal of 7 weirs in 2008-2010 Yearly run of sea trout smolts Year Data: DTU Aqua and Thorsten Møller Olesen
Stream length: 14 km 250 seatrout/km or 1 seatrout/4 m
Recommendations 1. Evaluateimpactsincludingindirecteffects 2. Remove the obstacleand restorethe naturalgradient 3. Try again it must be possible! 4. Start compromising.. thereareplentyopportunities for a life-long job
Literature: Look up Aarestrup, K. and you ll find most of what was presented here