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ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on May 27, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(7):1235-1247; doi:10.1093/icesjms/fsn087
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© 2008 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Characterization and classification of acoustically detected fish spatial distributions

Julian M. Burgos and John K. Horne

School of Fishery and Aquatic Science, University of Washington, Box 35520, Seattle, WA 98355, USA

Correspondence to J. M. Burgos: tel: +1 206 221 6864; fax: +1 206 685 7471; e-mail: jmburgos{at}u.washington.edu.

Burgos, J. M., and Horne, J. K. 2008. Characterization and classification of acoustically detected fish spatial distributions. – ICES Journal of Marine Science, 65: 1235–1247.

High-resolution, two-dimensional measurements of aquatic-organism density are collected routinely during echo integration trawl surveys. School-detection algorithms are commonly used to describe and analyse spatial distributions of pelagic and semi-pelagic organisms observed in echograms. This approach is appropriate for species that form well-defined schools, but is limited when used for species that form demersal layers or diffuse pelagic shoals. As an alternative to metrics obtained from school-detection algorithms, we used landscape indices to quantify and characterize spatial heterogeneity in density distributions of walleye pollock (Theragra chalcogramma). Survey transects were divided into segments of equal length and echo integrated at a resolution of 20 m (horizontal) and 1 m (vertical). A series of 20 landscape metrics was calculated in each segment to measure occupancy, patchiness, size distribution of patches, distances among patches, acoustic density, and vertical location and dispersion. Factor analysis indicated that the metric set could be reduced to four factors: spatial occupancy, aggregation, packing density, and vertical distribution. Cluster analysis was used to develop a 12-category classification typology for distribution patterns. Visual inspection revealed that spatial patterns of segments assigned to each type were consistent, but that there was considerable overlap among types.

Keywords: aggregations, echotrace classification, landscape indices, spatial pattern, walleye pollock

Received 26 July 2007; accepted 9 April 2008; advance access publication 27 May 2008.


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