Characterization and classification of acoustically detected fish spatial distributions
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 appro...
| Main Authors: | , |
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| Format: | Text |
| Language: | English |
| Published: |
2008
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.549.273 http://www.acoustics.washington.edu/hornefac/pubs/2008 burgos %26 horne - characterization.pdf |
| Summary: | 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 algor-ithms, 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, patchi-ness, size distribution of patches, distances among patches, acoustic density, and vertical location and dispersion. Factor analysis indi-cated 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. |
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