Diurnal variation in acoustic densities: why do we se less in the dark?
Introduction: In the Barents Sea, the echo abundance of demersal fish is about 50% higher at day than at night. Three possible reasons are: • Fish hide in the bottom dead zone at night. • Fish target strength changes due to pressure-related swim-bladder changes during vertical migration. • Fish targ...
Main Authors: | , , |
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Format: | Report |
Language: | English |
Published: |
ICES
2004
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Subjects: | |
Online Access: | http://hdl.handle.net/11250/106609 |
Summary: | Introduction: In the Barents Sea, the echo abundance of demersal fish is about 50% higher at day than at night. Three possible reasons are: • Fish hide in the bottom dead zone at night. • Fish target strength changes due to pressure-related swim-bladder changes during vertical migration. • Fish target strength varies due to higher variation in the tilt-angle distribution at night. It is very often claimed that the dead zone is most important. We argue that variation in tilt-angle may also be important. |
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