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Monitoring fish migration in Rivers

Helge Balk

Department of Physics. University of Oslo.

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River Tana River Tana

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River TanaRiver Tana

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Tornio (Se/Fi)Tornio (Se/Fi)

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River Reisa River Reisa (north Norw.)(north Norw.)

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River Fischa in River Fischa in AustriaAustria

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Echosounder in the river Echosounder in the river

Phase detector

AmplitudeDetector

4-ChTVG

1 size correction

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What we can do to increase the What we can do to increase the detection probability detection probability

Site selection

Bottom modification

Surface modification

Guide fish

Opening angle

Sound frequency

Estimate the DPF

Reduce the variation in the DPF

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If we detect a fish, What does it If we detect a fish, What does it mean?mean?

Echo sounder

?

Fish detection software

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Interpretation: DPF, noise and time Interpretation: DPF, noise and time expansionexpansion

Measure noise level as a function of time and range over years

Apply noise level as an overall fish size threshold

Use noise level to correct the number of fish within each size group

Apply time expansion to find the total fish abundance estimate

Noise level

Threshold

Intensity

1 2 3 4 5 6 7 8 9 10 Time

High noiselevel

Halt inrecording

High noiselevel

Echo sounder

Fish detector Meaningful

statistics

Interpreter

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Interpretation: Interpretation: Area expansionArea expansion

Echo sounder Meaningful

statistics!

Covered areaUncovered area

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0

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What did we cover?

Where did the fish pass?

Index or total run?

Fish detector

Interpreter

!

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Can we estimate TS in a river? Can we estimate TS in a river?

Spherical or cylindrical spreading? Corrupted vertical angular measurements? Additive noise? Can we compensate for swimming motion?

Can we compensate for fish aspect?

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Can we estimate TS in a river?Can we estimate TS in a river?

Alternative methods to establish the size?

Beam intensity mapping?

Apply reference targets?

Multiple narrow beams?

Multiple frequencies?

Aspect detection and correction?

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