Diurnal variation in acoustic densities: why do we see less in the dark?
Diurnal fluctuations in total integrated echo abundance and in vertical density profiles were examined using data from the Norwegian combined acoustic and bottom-trawl survey for demersal fish during winter in the Barents Sea. The total echo abundance was about 40%–50% higher at day than at night. A...
Published in: | Canadian Journal of Fisheries and Aquatic Sciences |
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Online Access: | http://hdl.handle.net/11250/108193 https://doi.org/10.1139/F04-161 |
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ftimr:oai:imr.brage.unit.no:11250/108193 2024-09-15T17:57:56+00:00 Diurnal variation in acoustic densities: why do we see less in the dark? Hjellvik, Vidar Godø, Olav Rune Tjøstheim, Dag 2005 1252337 bytes application/pdf http://hdl.handle.net/11250/108193 https://doi.org/10.1139/F04-161 eng eng urn:issn:0706-652X http://hdl.handle.net/11250/108193 http://dx.doi.org/10.1139/F04-161 2237-2254 61 Canadian Journal of Fisheries and Aquatic Sciences 11 cod torsk herring sild Journal article Peer reviewed 2005 ftimr https://doi.org/10.1139/F04-161 2024-07-31T03:37:25Z Diurnal fluctuations in total integrated echo abundance and in vertical density profiles were examined using data from the Norwegian combined acoustic and bottom-trawl survey for demersal fish during winter in the Barents Sea. The total echo abundance was about 40%–50% higher at day than at night. An unknown amount of fish was lost close to the seabed in the acoustic dead zone, but the systematic changes in the near-bottom vertical density profiles did not indicate that migration in and out of the dead zone was the major reason for the large diurnal differences in echo abundance. A more plausible explanation could be that diurnal changes in fish behaviour affect the mean acoustic target strength. Based on the present study, we recommend that the time series of acoustic surveys should be reanalysed, taking the diurnal bias into account. Any comparison of the fish densities indicated by trawl and acoustic surveys will suffer if this bias is not corrected. We believe that model development utilizing this type of information is crucial for future ecosystem-based monitoring. Article in Journal/Newspaper Barents Sea Institute for Marine Research: Brage IMR Canadian Journal of Fisheries and Aquatic Sciences 61 11 2237 2254 |
institution |
Open Polar |
collection |
Institute for Marine Research: Brage IMR |
op_collection_id |
ftimr |
language |
English |
topic |
cod torsk herring sild |
spellingShingle |
cod torsk herring sild Hjellvik, Vidar Godø, Olav Rune Tjøstheim, Dag Diurnal variation in acoustic densities: why do we see less in the dark? |
topic_facet |
cod torsk herring sild |
description |
Diurnal fluctuations in total integrated echo abundance and in vertical density profiles were examined using data from the Norwegian combined acoustic and bottom-trawl survey for demersal fish during winter in the Barents Sea. The total echo abundance was about 40%–50% higher at day than at night. An unknown amount of fish was lost close to the seabed in the acoustic dead zone, but the systematic changes in the near-bottom vertical density profiles did not indicate that migration in and out of the dead zone was the major reason for the large diurnal differences in echo abundance. A more plausible explanation could be that diurnal changes in fish behaviour affect the mean acoustic target strength. Based on the present study, we recommend that the time series of acoustic surveys should be reanalysed, taking the diurnal bias into account. Any comparison of the fish densities indicated by trawl and acoustic surveys will suffer if this bias is not corrected. We believe that model development utilizing this type of information is crucial for future ecosystem-based monitoring. |
format |
Article in Journal/Newspaper |
author |
Hjellvik, Vidar Godø, Olav Rune Tjøstheim, Dag |
author_facet |
Hjellvik, Vidar Godø, Olav Rune Tjøstheim, Dag |
author_sort |
Hjellvik, Vidar |
title |
Diurnal variation in acoustic densities: why do we see less in the dark? |
title_short |
Diurnal variation in acoustic densities: why do we see less in the dark? |
title_full |
Diurnal variation in acoustic densities: why do we see less in the dark? |
title_fullStr |
Diurnal variation in acoustic densities: why do we see less in the dark? |
title_full_unstemmed |
Diurnal variation in acoustic densities: why do we see less in the dark? |
title_sort |
diurnal variation in acoustic densities: why do we see less in the dark? |
publishDate |
2005 |
url |
http://hdl.handle.net/11250/108193 https://doi.org/10.1139/F04-161 |
genre |
Barents Sea |
genre_facet |
Barents Sea |
op_source |
2237-2254 61 Canadian Journal of Fisheries and Aquatic Sciences 11 |
op_relation |
urn:issn:0706-652X http://hdl.handle.net/11250/108193 http://dx.doi.org/10.1139/F04-161 |
op_doi |
https://doi.org/10.1139/F04-161 |
container_title |
Canadian Journal of Fisheries and Aquatic Sciences |
container_volume |
61 |
container_issue |
11 |
container_start_page |
2237 |
op_container_end_page |
2254 |
_version_ |
1810434159220359168 |