Modelling Diurnal Variation in Bottom Trawl Catches and Potential Application in Surveys
Diurnal variability in bottom trawl survey catches may influence the quality of the survey results when not taken properly into account. This is especia]!.y the case if diurnal effects vary substantiaIly from year to year. In this study, catches of cod from the winter and autumn surveys in the Baren...
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ftimr:oai:imr.brage.unit.no:11250/100411 2023-05-15T15:39:02+02:00 Modelling Diurnal Variation in Bottom Trawl Catches and Potential Application in Surveys Hjellvik, Vidar Godø, Olav Rune Tjøstheim, Dag 1999 3324354 bytes application/pdf http://hdl.handle.net/11250/100411 eng eng ICES ICES CM documents 1999/J:06 http://hdl.handle.net/11250/100411 28 s. bottom trawl bunntrål cod torsk catch fangst VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Fisheries technology: 924 VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Resource biology: 921 Working paper 1999 ftimr 2021-09-23T20:15:36Z Diurnal variability in bottom trawl survey catches may influence the quality of the survey results when not taken properly into account. This is especia]!.y the case if diurnal effects vary substantiaIly from year to year. In this study, catches of cod from the winter and autumn surveys in the Barents Sea during the years 1985-1999 were explored using both parametric and nonparametric statistical methods. Diurnal variation in winter has a smooth threshold form with a high catch period at daytime lasting approximately 8 hours. Small cod seems to be triggered more by the clock than by the time of sunrise. In the autumn the diurnal variation is much less distinct. Both in winter and autumn the effect tends to decrease with fish size and increase with depth. Diurnal effects on small cod vary substantially from year to year, whereas larger fish show a higher degree of stability. We suggest a bootstrap based method for adjusting the catches for diurnal variation. This can be applied to the catches prior to the calculation of indices, and also includes measures of the uncertainty. Analyses are done by size groups and the effects of size dependent vertical migration dynamics and catching efficiency are discussed and considered in relation to the performance of the simultaneous acoustic survey. Report Barents Sea Institute for Marine Research: Brage IMR Barents Sea |
institution |
Open Polar |
collection |
Institute for Marine Research: Brage IMR |
op_collection_id |
ftimr |
language |
English |
topic |
bottom trawl bunntrål cod torsk catch fangst VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Fisheries technology: 924 VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Resource biology: 921 |
spellingShingle |
bottom trawl bunntrål cod torsk catch fangst VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Fisheries technology: 924 VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Resource biology: 921 Hjellvik, Vidar Godø, Olav Rune Tjøstheim, Dag Modelling Diurnal Variation in Bottom Trawl Catches and Potential Application in Surveys |
topic_facet |
bottom trawl bunntrål cod torsk catch fangst VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Fisheries technology: 924 VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Resource biology: 921 |
description |
Diurnal variability in bottom trawl survey catches may influence the quality of the survey results when not taken properly into account. This is especia]!.y the case if diurnal effects vary substantiaIly from year to year. In this study, catches of cod from the winter and autumn surveys in the Barents Sea during the years 1985-1999 were explored using both parametric and nonparametric statistical methods. Diurnal variation in winter has a smooth threshold form with a high catch period at daytime lasting approximately 8 hours. Small cod seems to be triggered more by the clock than by the time of sunrise. In the autumn the diurnal variation is much less distinct. Both in winter and autumn the effect tends to decrease with fish size and increase with depth. Diurnal effects on small cod vary substantially from year to year, whereas larger fish show a higher degree of stability. We suggest a bootstrap based method for adjusting the catches for diurnal variation. This can be applied to the catches prior to the calculation of indices, and also includes measures of the uncertainty. Analyses are done by size groups and the effects of size dependent vertical migration dynamics and catching efficiency are discussed and considered in relation to the performance of the simultaneous acoustic survey. |
format |
Report |
author |
Hjellvik, Vidar Godø, Olav Rune Tjøstheim, Dag |
author_facet |
Hjellvik, Vidar Godø, Olav Rune Tjøstheim, Dag |
author_sort |
Hjellvik, Vidar |
title |
Modelling Diurnal Variation in Bottom Trawl Catches and Potential Application in Surveys |
title_short |
Modelling Diurnal Variation in Bottom Trawl Catches and Potential Application in Surveys |
title_full |
Modelling Diurnal Variation in Bottom Trawl Catches and Potential Application in Surveys |
title_fullStr |
Modelling Diurnal Variation in Bottom Trawl Catches and Potential Application in Surveys |
title_full_unstemmed |
Modelling Diurnal Variation in Bottom Trawl Catches and Potential Application in Surveys |
title_sort |
modelling diurnal variation in bottom trawl catches and potential application in surveys |
publisher |
ICES |
publishDate |
1999 |
url |
http://hdl.handle.net/11250/100411 |
geographic |
Barents Sea |
geographic_facet |
Barents Sea |
genre |
Barents Sea |
genre_facet |
Barents Sea |
op_source |
28 s. |
op_relation |
ICES CM documents 1999/J:06 http://hdl.handle.net/11250/100411 |
_version_ |
1766370489922486272 |