1 Monitoring fish migration in Rivers Helge Balk Department of Physics. University of Oslo.

2 River Tana

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4 Tornio (Se/Fi)

5 River Reisa (north Norw.)

6 River Fischa in Austria

7 Echosounder in the river Phase detector Amplitude Detector 4-Ch TVG 1 size correction

8 What we can do to increase the detection probability Site selection Bottom modification Surface modification Guide fish Opening angle Sound frequency Estimate the DPF Reduce the variation in the DPF

9 If we detect a fish, What does it mean? Echo sounder ? Fish detection software

10 Interpretation: DPF, noise and time expansion 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 Echo sounder Fish detector Meaningful statistics Interpreter

11 Interpretation: Area expansion Echo sounder Meaningful statistics! What did we cover? Where did the fish pass? Index or total run? Fish detector Interpreter !

12 Can we estimate TS in a river? u Spherical or cylindrical spreading? u Corrupted vertical angular measurements? u Additive noise? u Can we compensate for swimming motion? u Can we compensate for fish aspect?

13 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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