Management of wild salmon populations in Denmark Anders Koed, Danish Technical University, Section for Freshwater Fisheries and Ecology
Outline 1. The Danish salmon in a historical perspective what vent wrong? 2. How the (some) salmon populations were saved...
Annual catches of salmon in the estuary of River Skjern, 1900-1978 Number of salmon caught 700 600 500 400 300 200 100 0 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Otterstrøm (1938) and Statistic yearbooks, the Ministery of Fisheries
River Skjern Å land claim project implemented in the 1960 erne Impaired migration and spawning and nursery areas of salmon disappeared
1940 Poulsen 1935 Salmon catches in River Gudenåen 1850 1930 1930 1920 1910 1900 1890 1880 1870 1860 1850 1840 1400 1200 1000 800 600 400 200 0 Number caught
Power plant development in 1921 River blockage prevented the salmon in reaching the spawning areas the River Gudenå salmon vent extinct
Cause (what vent wrong): Sewage and waste-water caused habitat loss and habitat degradation. This was stopped in 1980 ties.
Cause (what vent wrong): Dredging and canalization, 1700 2011. Caused habitat loss and habitat degradation.
Cause (what vent wrong): Mills ponds, 1000 1850. Caused habitat loss and impaired migration.
Cause (what vent wrong): Hydropower development, 1920 1970. Caused habitat loss and impaired migration.
Cause (what vent wrong): Fish farming, 1894 1975. Caused habitat loss, habitat degradation and impaired migration. About 800 in 1970, 250 left today.
The causes were identified by research. Example negative effects of weirs and barriers Loss and delay of smolts Loss and delay of spawners Loss of habitats Jepsen, Nielsen & Deacon (2005) Svendsen, Koed & Aarestrup (2004) Aarestrup & Koed (2003) Koed, Jepsen, Aarestrup & Nielsen (2002)
Smolt loss at barriers Types Number Avg. smolt loss investigated (%) Mills 5 30 Fish farms 38 42 Hydro Power stations 7 82 Loss when passing 3 fish farms in a river: (1-(1-0.42) 3 )= 80 %! Aarestrup & Koed (2003)
Predation in fish farms
Delay desmoltification
...the negative trend can be reversed. 3500 3000 2500 2000 1500 1000 500 0 Salmon spawning-run - River Skjern 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007
Wild sea trout smolt production in Denmark, Baltic area 250000 200000 150000 100000 50000 0 2000 2001 2002 2003 2004 2005 2006 2007
using original fish in restored habitats
Stocking using original fish in restored habitats In the 1980 ies the salmon populations in Denmark were believed to have gone extinct, except for the one in River Skjern... River Storå River Gudenå River Skjern Å River Varde Å River Sneum Å River Kongeå River Ribe Å River Brede Å River Vidå
River Storå development in catches, Stocking of non native orgin
using original fish in restored habitats DNA from old scales compared with DNA collected during 1993-2003 Old DNA (1910-1913) Present =
using original fish in restored habitats 4 indigenous populations left in 1999! River Storå River Gudenå River Skjern River Varde River Sneum River Kongeå River Ribe Å River Brede River Vidå Nielsen, Hansen & Bach (2001)
River Storå development in catches, Stocking of native vs non native origin
Still need for a supportive stocking programme...
Salmon are brought to the hatchery
Fry..
Stocking of ½ and 1 yearlings
Film by Bo Skelmose
River Skjern Å restoration project largest in Northern Europe Povl Toft
..migration barriers have been removed and habitats restored
Research based management is central for successful restoration of fish populations this has saved the Danish wild salmon: Regulation of the gear fishery and a quota system in the rivers. Assessment programme of the population size quarto annual. A focused and knowledge based stocking programme. River restoration, e.g. removing obstacles.
this has taken us here.
Habitat restoration and using original fish Angler-caught salmon 1996-1997 and 2004-2010 Number of salmon caught New supportive breeding procedure implemented: Only F1 and indigenous fish
Successful restoration of salmon populations is based on knowledge obtained from research and monitoring Salmon spawning-run - River Skjern 3500 3000 2500 2000 1500 Restoration of habitats 1000 500 0 1901 1906 1911 1916 1921 1926 1931 1936 1941 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006 Cormorant culling programme in the estuary Supportive breeding procedure optimised: F1, indigenous fish, when reintroducing - geographic closest population Restrictive regulation of the Fishery - Estuary: no-take zone - Restrictive regulation of the commercial fishery - River: restricted period, catch limit, C&R
Research based management is central for successful restoration of fish populations
In 2004 the Danish Management Plan for Salmon was published it is a unique tool describing which measures should be taken to secure the Danish salmon populations
The Management Model for Freshwater Fishes in Denmark Goal: Self-sustaining populations Management system - Habitat restoration - Population restoration Research and Monitoring Legislation - Ministry of Fisheries - Ministry of the Environment Stakeholders - Anglers - Fishermen
Research is swiftly feed into management... Goal: Self-sustaining populations Management system - Habitat restoration - Population restoration Research and Monitoring Legislation - Ministry of Fisheries - Ministry of the Environment Stakeholders - Anglers - Fishermen
Thanks for your attention!