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Can subjective evaluation of echograms improve correlation between bottom trawl and acoustic densities?

Godø, Olav Rune; Hjellvik, Vidar; Greig, Tony; Beare, Douglas
Working paper
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URI
http://hdl.handle.net/11250/100591
Date
2004
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  • ICES CM documents authored by IMR scientists (1949-2011) [3138]
Abstract
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, accumulated experience on the

visual appearance of various species on the echograms combined with species and

size information from the trawl is used to scrutinize the echogram and split the

observed total acoustic density to species or groups of species.

In this paper, combined bottom trawl – acoustic survey data collected by Scotland and

Norway from the North and the Barents Seas are used to study correlations between

bottom trawl catches and the acoustic density measures logged from vessel mounted

transducers during the trawl operations. We want to evaluate if classifying echo traces

by species or groups of species prior to the analysis can improve the correlations

between trawl catches and acoustic densities. Although the classification process

contains elements of subjectivity, it is based on characteristics of the echo traces,

temporal changes in the echograms, geographic location and time of day as well as

species and size compositions of the trawl catches.

Initial results indicate that scrutinized information improves the correlation between

trawl and acoustic density information and that harmonized rules for the scrutinizing

procedures should be developed.
Publisher
ICES
Series
ICES CM documents
2004/ R:23

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