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Fish M igration… from Sea to Sourc e
Critical problems for migratory fish in the North Sea region
from a Danish perspective
By
Kim Aarestrup, Anders Koed & Niels Jepsen
Technical University of Denmark
Fish M igration… from Sea to Sourc e
Overview:
Management setup in Denmark
A fundamental aspect
Overall problems
Weirs
How to obtain information on moving animals (you can’t see)
Examples of studies and consequences of result
Does recommendations work?
Fish M igration… from Sea to Sourc e
“The Management Model for Diadromous Fish populations 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
Fish M igration… from Sea to Sourc e
Fish M igration… from Sea to Sourc e
Gross 1987
Fish M igration… from Sea to Sourc e
Migrating
Sea residence
Downstream migration
Spawning
Hatching
Spawning migration
Lifecycle – a fundamental aspect
Fish M igration… from Sea to Sourc e
Causes of the decline
Sewage and waste-water caused habitat loss and habitat degradation.
Dredging and canalization caused habitat loss and habitat degradation.
Over fishing
Fish M igration… from Sea to Sourc e
Establishment of Mill ponds (1000 – 1850), Hydropower development (1920 – 1970) and Fish farming (1894 – 1975).
Caused habitat loss, habitat degradation and impaired migration.
Fish M igration… from Sea to Sourc e
A Significant problem
Fish M igration… from Sea to Sourc e
0
100
200
300
400
500
600
70019
01
1905
1909
1913
1917
1921
1925
1929
1933
1937
1941
1945
1949
1953
1957
1961
1965
1969
1973
1977
1981
Ant
al la
ks fa
nget
i R
ingk
øbin
g F
jord
Otterstrøm (1938) and Statistic yearbooks, the Ministery of Fisheries
Num
ber
of
salm
on c
augh
t in
Rin
gkø
bing
Fjo
rd
Fish M igration… from Sea to Sourc e
Number of rivers and streams with trout populations in Denmark - retrospective
Fish M igration… from Sea to Sourc e
Investigating the migration of fish – methods?
TELEMETRY
Limitations: Low numbersTagging and handling effectsAnimal welfare/ethicsCost and labour intensive
Advantages:Only way to get this type of informationClear results Easy to understandEasy to explain
Fish M igration… from Sea to Sourc e
Release 1
Release 2
WeirWeir
Trap
• Loss calculated as the relative difference in recapture.
• Delay Calculated as the difference in 50 % fractile
• Loss can be related to e.g.. Flow released for fish passage
Fish M igration… from Sea to Sourc e
Types Number investigated
Avg. smolt loss (%)
Mills 5 30
Fish farms 38 42
Hydro Power stations 7 82
Smolt loss at barriers
Aarestrup et al. In prep
Fish M igration… from Sea to Sourc e
TANGE RESERVIOR
ALS
Dam
Hydro-plant
Ans Bridge
ALS
ALS
Release siteSmolttrap
Kongensbro
Fish M igration… from Sea to Sourc e
0
10
20
30
40
50
Trout Salmon
Sm
olt
loss
km-1
(%
)
River Reservior/Lake
N=8
N=8
N=10
N=4
Fish M igration… from Sea to Sourc e
Loss is cumulative!
Number of weirs to pass
Sur
viva
l in
perc
ent
Fish M igration… from Sea to Sourc e
• River Villestrup Å, Total 22 m, app. 9 m i 6 weirs (app. 40 %)
Weir A
Water surface
Weir B
Distance from source
Hei
ght a
bove
sea
-lev
el
Stream bed
Another serious aspect
Fish M igration… from Sea to Sourc e
..migration barriers have been removed and habitats restored
Fish M igration… from Sea to Sourc e
Successful restoration of salmon populations is based on knowledge obtained from research and monitoring
Fish M igration… from Sea to Sourc e
Fish M igration… from Sea to Sourc e
Fish M igration… from Sea to Sourc e
Fish M igration… from Sea to Sourc e
Population development sea trout – River Villestrup
1330
2611
8 36333
0
500
1000
1500
2000
2500
3000
1989 1999 2004 2007 Completerestoration
(model)
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