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

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500

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70019

01

1905

1909

1913

1917

1921

1925

1929

1933

1937

1941

1945

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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)