Blar i ICES CM documents authored by IMR scientists (1949-2011) på emneord "bottom trawl"
Viser treff 1-20 av 57
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A method to reduce survey bottom trawl variability
(ICES CM Documents;1991/B:39, Working paper, 1991)A technique for limiting the variability of trawl doorspread is described. In addition, modifications of trawling technique which enable the doors to stay upright and maintain constant ground contact under different ... -
A vessel specific bias in echo sounder recordings during trawling
(ICES CM Documents;2004/R:35, Working paper, 2004) -
Acoustic and Bottom Trawl Surveys; How Much Information Do They Provide for Assessing the Northeast Arctic Cod Stock?
(ICES CM documents, Working paper, 1999)Acoustic and bottom trawl surveys of the Northeast Arctic cod stock provide fishery independent estimates of trends in abundance and population characteristics. Given the recent uncertainties in the catch based assessment ... -
An evaluation of the IMR Summer Bottom Trawl Survey in the Barents Sea
(ICES CM Documents;2001/P:16, Working paper, 2001)Summary: A committee was formed to evaluate the Institute of Marine Research summer survey in the Barents Sea, which has been conducted annually since 1995. The primary focus of the committee was the survey’s importance ... -
Analysis of CPUE from the Norwegian bottom trawl fleet
(ICES CM Documents;2000/W:14, Working paper, 2000)Commercial logbooks with catch and effort data have been collected and recorded by the Norwegian Direcorate of Fisheries since 1971. Annual age segregated CPUE indices are calculated with different methods for North-east ... -
Avoidance reactions of ultrasonic tagged cod during bottom trawling in shallow water
(ICES CM Documents;1991/B:41, Working paper, 1991)Introduction: Observations made by echo sounder (Ona 1988) have shown that cod (Gadus morhua L.) may avoid an approaching survey vessel horizontally and vertically. However, there has been a lack of information on the ... -
Can subjective evaluation of echograms improve correlation between bottom trawl and acoustic densities?
(ICES CM documents, Working paper, 2004)Direct comparison of acoustic densities and trawl catches involves fundamental difficulties related to species and size selectivity of the trawl and efficiency of the acoustic instrumentation. In some surveys, therefore, ... -
Catch comparison between rockhoppers and bobbins ground gear on the Norwegian bottom sampling trawl
(ICES CM Documents;1988/B:31, Working paper, 1988)In a study aimed at improving the reliability of the Norwegian bottom sampling trawl, comparative fishing between standard bobbins gear and rockhopper ground gear were carried out in the Barents Sea. The catch ratios ... -
Changes in acoustic abundance - a signal indicatior for stock dynamics for cod (Gadus morhua)
(ICES CM documents, Working paper, 1999)To be able to take the proper and timely management actions, it is crucial to reliably defect major changes in trends of fish stock abundance. For the assessment of Northeast Arctic cod, the Norwegian bottom trawl survey ... -
Comparison between "underway" and "on station" acoustic measurements made during bottom trawl surveys
(ICES CM Documents;2002/J:3, Working paper, 2002)It becomes in many cases, routine, to collect acoustic data during bottom trawl surveys, both during and between trawls providing “on station” and “underway” acoustic data. Still, the combination of trawl and acoustic data ... -
Density dependent catchability in bottom trawl surveys
(ICES CM Documents;1997/W:16, Working paper, 1997)Fish form schools, layer or patches in which the individual fish's behaviour is not independent of its neighbours movements. On the other hand, at low densities fish may have the freedom to act as single individuals ... -
Diurnal changes in bottom trawl catches and vertical fish distribution
(ICES CM Documents;1988/B:32, Working paper, 1988)Bottom sampling trawl catches and acoustic abundance estimates of North-East Arctic cod and haddock in the Barents Sea were collected and examined according to time of day. The trawl catches were at average larger by day ... -
Diurnal variation in bottom trawl survey catches: does it pay to adjust?
(ICES CM Documents;2001/Q:11, Working paper, 2001)We have studied the diurnal bias of bottom trawl survey catches with the purpose of adjusting for it and thereby improving the accuracy of abundance estimates. The correction term is estimated with uncertainty, and thus ... -
Diurnal variation models of bottom trawl survey catches parameterised by using commercial CPUE data
(ICES CM Documents;2004/R:41, Working paper, 2004)Introduction: Diurnal variation is observed in almost all marine surveys and can cause biased abundance and length frequency estimates. Symmetric logistic models developed by Hjellvik et al. (2001) were utilized to ... -
Estimation of unreported catch in a commercial trawl fishery
(ICES CM Documents;1991/D:12, Working paper, 1991)The Institute of Marine Research (IMR), Bergen, has carried out combined bottom trawl and acoustic surveys for cod in the Barents Sea since 1981. Commercial statistics are collected routinely for this area through the ... -
Experiences using the constraint technique on bottom trawl doors
(ICES CM Documents;1993/B:18, Working paper, 1993)The constraint technique, i.e. using a rope between the warps, has the intention of minimizing the variability in trawl geometry with depth. Experiments with the constraint technique on two different bottom trawls used ... -
In situ determination of bottom trawl ground gear contact
(ICES CM documents, Working paper, 2001)Exact definition of towed distance with proper ground gear contact is an essential parameter in bottom trawl swept area estimates of fish abundance. Errors in this key parameter may lead to a first order bias in abundance ... -
Minimalistic surveys clear the way for priorities in the ecosystem approach
(ICES CM documents;2009/I:20, Working paper, 2009)Standardized surveys are an integral part of most fish stock assessments. Ship time is expensive and new demands set by the ecosystem approach challenge present survey and sampling strategies with respect to coverage of ... -
Modelling Diurnal Variation in Bottom Trawl Catches and Potential Application in Surveys
(ICES CM documents, Working paper, 1999)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 ... -
Near-bottom sampling with bottom and pelagic trawls
(ICES CM Documents;1987/B:15, Working paper, 1987)The Institute of Marine Research, Bergen, has carried out combined bottom trawl and acoustic surveys for cod and haddock in the Barents Sea - Svalbard area since 1981. These investigations have demonstrated clearly that ...