Diurnal variation in acoustic densities: why do we see less in the dark? ...

• Main Authors: Hjellvik, V., Godø, O.R., Tjøstheim, D.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: ASC 2004 - R - Theme session 2024
• Subjects: Fisheries and aquaculture; Technologies and data; Barents Sea
• Online Access: https://dx.doi.org/10.17895/ices.pub.25349773; https://ices-library.figshare.com/articles/conference_contribution/Diurnal_variation_in_acoustic_densities_why_do_we_see_less_in_the_dark_/25349773

No abstracts are to be cited without prior reference to the author.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. ...