HELCOM Task force on migratory fish species Copenhagen 15-11-2016 - - PowerPoint PPT Presentation

HELCOM Task force on migratory fish species

Copenhagen 15-11-2016

Stig Pedersen, DTU Aqua National Institute of Aquatic Resources, Technical University of Denmark 1

Danish streams

• Stream length 70,000 km
• Lowland streams
• Majority of streams small (by length
• ca. 59 %)
• Good chemical water quality
• High productivity
• General increase in quality over

past 30 years

• Physical stream conditions

formally regulated for each river stipulating shape, maintenance scheme etc.

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Anthropogenic influences

– Ditching, straigthening, culverting

• purpose: land use and regulation of water level in farm land

– Construction of barriers

• Purpose: energy, fish farming

– Maintenance

• Purpose: Ensure draining and avoiding flooding

Allmost all streams (98%) affected by man:

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Major effects from anthropogenic actions

• Straightening

– Increased / changed slope – Increased erosion – Increased content of fine sediment (sand) – Lack of gravel for salmonid spawning – Reduced productive area

• Construction of barriers

– Inhibiting migration – Changing stream conditions up and downstream

• Maintenance

– Affecting biological content and diversity – Affecting shape and flow – habitat composition and content

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Restoration methods used

• Straightening

– Re-meandering – effect on potentially all elements – Addition of gravel – salmonid spawning – Establish sand traps – Establish wide river banks without culture

• Construction of barriers

– Establish fish ladders – Establish nature like by-passes – Complete removal of barriers

• Maintenance

– Shading to reduce growth of stream vegetation – Selective / network / main current path cutting of vegetation – Reduce intensity of weed cutting

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Remeandering River Gels Å 1989

2015 1954

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Remeandering and creating nature like by-pass at fish farm River Storå

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‘Natural’ by-pass at fish farm River Storå

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Loss of smolt at downstream migration past barriers

Barrier type

• Avg. Smolt

loss (%) Mills (n=5) 30 Fish farms (n=38) 42 Hydro power plants (n=7) 82

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Smolt loss in streams and reservoirs

10 20 30 40 50 Trout Salmon Smolt loss km-1 (%) River Reservior/Lake

N=8 N=8 N=4 N=10

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Barriers - Loss of habitat + elevated smolt mortality

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Loss of gradient in weirs

Aarestrup & Koed 2006

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• 1. Barrier removed

2 – 7’th Barrer removed

Removal of barriers – Villestrup Å

Number of smolt

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Before and after removal of weir in Kolding Å

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Before and after removal of weir in Kolding Å

20 40 60 80 100 120 2008 2009 Density of 0+ trout

Removal of barrier resulted in appox. 300 spawning sea trout in first winter and trout densities in upstream sites increased approx. 5 times

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Restoration on a smaller scale

Addition of spawning gravel – also increases habitat variation Many small projects by NGO’s (angler associations) Financial support from the Fish Care Management program Annual budget 65,000 EURO

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Restoration on a smaller scale

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Restoration on a smaller scale

Reduced maintenance and erosion

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The Fish Care Management programme

• Objective:

Forward natural reproduction of fish populations – Stocking – Habitat improvement – Management initiatives – Research

• Funded by a national

license from

– Anglers: 25 EURO / year – Recreational fishermen (fixed gear): 40 EURO / year

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Plans for Fish Care

• 7000 sites monitored

every 7-8 years (1000 sites /year)

• 70 % of sites are

fished

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Plans for fish care

• Publish a report for each river or

group of smaller rivers

• Recommendations issued with focus on

habitat improvement

• Stocking of trout only with local strains in order

to reintroduce (and enhance) populations

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Distributing information

+ two fulltime consultants advising both NGO’s and authorities

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